--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/share/classes/java/util/concurrent/CountedCompleter.java	Wed Aug 22 18:22:03 2012 -0700
@@ -0,0 +1,480 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+package java.util.concurrent;
+
+/**
+ * A resultless {@link ForkJoinTask} with a completion action
+ * performed when triggered and there are no remaining pending
+ * actions. Uses of CountedCompleter are similar to those of other
+ * completion based components (such as {@link
+ * java.nio.channels.CompletionHandler}) except that multiple
+ * <em>pending</em> completions may be necessary to trigger the {@link
+ * #onCompletion} action, not just one. Unless initialized otherwise,
+ * the {@link #getPendingCount pending count} starts at zero, but may
+ * be (atomically) changed using methods {@link #setPendingCount},
+ * {@link #addToPendingCount}, and {@link
+ * #compareAndSetPendingCount}. Upon invocation of {@link
+ * #tryComplete}, if the pending action count is nonzero, it is
+ * decremented; otherwise, the completion action is performed, and if
+ * this completer itself has a completer, the process is continued
+ * with its completer.  As is the case with related synchronization
+ * components such as {@link Phaser} and {@link
+ * java.util.concurrent.Semaphore} these methods affect only internal
+ * counts; they do not establish any further internal bookkeeping. In
+ * particular, the identities of pending tasks are not maintained. As
+ * illustrated below, you can create subclasses that do record some or
+ * all pended tasks or their results when needed.
+ *
+ * <p>A concrete CountedCompleter class must define method {@link
+ * #compute}, that should, in almost all use cases, invoke {@code
+ * tryComplete()} once before returning. The class may also optionally
+ * override method {@link #onCompletion} to perform an action upon
+ * normal completion, and method {@link #onExceptionalCompletion} to
+ * perform an action upon any exception.
+ *
+ * <p>A CountedCompleter that does not itself have a completer (i.e.,
+ * one for which {@link #getCompleter} returns {@code null}) can be
+ * used as a regular ForkJoinTask with this added functionality.
+ * However, any completer that in turn has another completer serves
+ * only as an internal helper for other computations, so its own task
+ * status (as reported in methods such as {@link ForkJoinTask#isDone})
+ * is arbitrary; this status changes only upon explicit invocations of
+ * {@link #complete}, {@link ForkJoinTask#cancel}, {@link
+ * ForkJoinTask#completeExceptionally} or upon exceptional completion
+ * of method {@code compute}. Upon any exceptional completion, the
+ * exception may be relayed to a task's completer (and its completer,
+ * and so on), if one exists and it has not otherwise already
+ * completed.
+ *
+ * <p><b>Sample Usages.</b>
+ *
+ * <p><b>Parallel recursive decomposition.</b> CountedCompleters may
+ * be arranged in trees similar to those often used with {@link
+ * RecursiveAction}s, although the constructions involved in setting
+ * them up typically vary. Even though they entail a bit more
+ * bookkeeping, CountedCompleters may be better choices when applying
+ * a possibly time-consuming operation (that cannot be further
+ * subdivided) to each element of an array or collection; especially
+ * when the operation takes a significantly different amount of time
+ * to complete for some elements than others, either because of
+ * intrinsic variation (for example IO) or auxiliary effects such as
+ * garbage collection.  Because CountedCompleters provide their own
+ * continuations, other threads need not block waiting to perform
+ * them.
+ *
+ * <p> For example, here is an initial version of a class that uses
+ * divide-by-two recursive decomposition to divide work into single
+ * pieces (leaf tasks). Even when work is split into individual calls,
+ * tree-based techniques are usually preferable to directly forking
+ * leaf tasks, because they reduce inter-thread communication and
+ * improve load balancing. In the recursive case, the second of each
+ * pair of subtasks to finish triggers completion of its parent
+ * (because no result combination is performed, the default no-op
+ * implementation of method {@code onCompletion} is not overridden). A
+ * static utility method sets up the base task and invokes it:
+ *
+ * <pre> {@code
+ * class MyOperation<E> { void apply(E e) { ... }  }
+ *
+ * class ForEach<E> extends CountedCompleter {
+ *
+ *     public static <E> void forEach(ForkJoinPool pool, E[] array, MyOperation<E> op) {
+ *         pool.invoke(new ForEach<E>(null, array, op, 0, array.length));
+ *     }
+ *
+ *     final E[] array; final MyOperation<E> op; final int lo, hi;
+ *     ForEach(CountedCompleter p, E[] array, MyOperation<E> op, int lo, int hi) {
+ *         super(p);
+ *         this.array = array; this.op = op; this.lo = lo; this.hi = hi;
+ *     }
+ *
+ *     public void compute() { // version 1
+ *         if (hi - lo >= 2) {
+ *             int mid = (lo + hi) >>> 1;
+ *             setPendingCount(2); // must set pending count before fork
+ *             new ForEach(this, array, op, mid, hi).fork(); // right child
+ *             new ForEach(this, array, op, lo, mid).fork(); // left child
+ *         }
+ *         else if (hi > lo)
+ *             op.apply(array[lo]);
+ *         tryComplete();
+ *     }
+ * } }</pre>
+ *
+ * This design can be improved by noticing that in the recursive case,
+ * the task has nothing to do after forking its right task, so can
+ * directly invoke its left task before returning. (This is an analog
+ * of tail recursion removal.)  Also, because the task returns upon
+ * executing its left task (rather than falling through to invoke
+ * tryComplete) the pending count is set to one:
+ *
+ * <pre> {@code
+ * class ForEach<E> ...
+ *     public void compute() { // version 2
+ *         if (hi - lo >= 2) {
+ *             int mid = (lo + hi) >>> 1;
+ *             setPendingCount(1); // only one pending
+ *             new ForEach(this, array, op, mid, hi).fork(); // right child
+ *             new ForEach(this, array, op, lo, mid).compute(); // direct invoke
+ *         }
+ *         else {
+ *             if (hi > lo)
+ *                 op.apply(array[lo]);
+ *             tryComplete();
+ *         }
+ *     }
+ * }</pre>
+ *
+ * As a further improvement, notice that the left task need not even
+ * exist.  Instead of creating a new one, we can iterate using the
+ * original task, and add a pending count for each fork:
+ *
+ * <pre> {@code
+ * class ForEach<E> ...
+ *     public void compute() { // version 3
+ *         int l = lo,  h = hi;
+ *         while (h - l >= 2) {
+ *             int mid = (l + h) >>> 1;
+ *             addToPendingCount(1);
+ *             new ForEach(this, array, op, mid, h).fork(); // right child
+ *             h = mid;
+ *         }
+ *         if (h > l)
+ *             op.apply(array[l]);
+ *         tryComplete();
+ *     }
+ * }</pre>
+ *
+ * Additional improvements of such classes might entail precomputing
+ * pending counts so that they can be established in constructors,
+ * specializing classes for leaf steps, subdividing by say, four,
+ * instead of two per iteration, and using an adaptive threshold
+ * instead of always subdividing down to single elements.
+ *
+ * <p><b>Recording subtasks.</b> CountedCompleter tasks that combine
+ * results of multiple subtasks usually need to access these results
+ * in method {@link #onCompletion}. As illustrated in the following
+ * class (that performs a simplified form of map-reduce where mappings
+ * and reductions are all of type {@code E}), one way to do this in
+ * divide and conquer designs is to have each subtask record its
+ * sibling, so that it can be accessed in method {@code onCompletion}.
+ * For clarity, this class uses explicit left and right subtasks, but
+ * variants of other streamlinings seen in the above example may also
+ * apply.
+ *
+ * <pre> {@code
+ * class MyMapper<E> { E apply(E v) {  ...  } }
+ * class MyReducer<E> { E apply(E x, E y) {  ...  } }
+ * class MapReducer<E> extends CountedCompleter {
+ *     final E[] array; final MyMapper<E> mapper;
+ *     final MyReducer<E> reducer; final int lo, hi;
+ *     MapReducer sibling;
+ *     E result;
+ *     MapReducer(CountedCompleter p, E[] array, MyMapper<E> mapper,
+ *                MyReducer<E> reducer, int lo, int hi) {
+ *         super(p);
+ *         this.array = array; this.mapper = mapper;
+ *         this.reducer = reducer; this.lo = lo; this.hi = hi;
+ *     }
+ *     public void compute() {
+ *         if (hi - lo >= 2) {
+ *             int mid = (lo + hi) >>> 1;
+ *             MapReducer<E> left = new MapReducer(this, array, mapper, reducer, lo, mid);
+ *             MapReducer<E> right = new MapReducer(this, array, mapper, reducer, mid, hi);
+ *             left.sibling = right;
+ *             right.sibling = left;
+ *             setPendingCount(1); // only right is pending
+ *             right.fork();
+ *             left.compute();     // directly execute left
+ *         }
+ *         else {
+ *             if (hi > lo)
+ *                 result = mapper.apply(array[lo]);
+ *             tryComplete();
+ *         }
+ *     }
+ *     public void onCompletion(CountedCompleter caller) {
+ *         if (caller != this) {
+ *            MapReducer<E> child = (MapReducer<E>)caller;
+ *            MapReducer<E> sib = child.sibling;
+ *            if (sib == null || sib.result == null)
+ *                result = child.result;
+ *            else
+ *                result = reducer.apply(child.result, sib.result);
+ *         }
+ *     }
+ *
+ *     public static <E> E mapReduce(ForkJoinPool pool, E[] array,
+ *                                   MyMapper<E> mapper, MyReducer<E> reducer) {
+ *         MapReducer<E> mr = new MapReducer<E>(null, array, mapper,
+ *                                              reducer, 0, array.length);
+ *         pool.invoke(mr);
+ *         return mr.result;
+ *     }
+ * } }</pre>
+ *
+ * <p><b>Triggers.</b> Some CountedCompleters are themselves never
+ * forked, but instead serve as bits of plumbing in other designs;
+ * including those in which the completion of one of more async tasks
+ * triggers another async task. For example:
+ *
+ * <pre> {@code
+ * class HeaderBuilder extends CountedCompleter { ... }
+ * class BodyBuilder extends CountedCompleter { ... }
+ * class PacketSender extends CountedCompleter {
+ *     PacketSender(...) { super(null, 1); ... } // trigger on second completion
+ *     public void compute() { } // never called
+ *     public void onCompletion(CountedCompleter caller) { sendPacket(); }
+ * }
+ * // sample use:
+ * PacketSender p = new PacketSender();
+ * new HeaderBuilder(p, ...).fork();
+ * new BodyBuilder(p, ...).fork();
+ * }</pre>
+ *
+ * @since 1.8
+ * @author Doug Lea
+ */
+public abstract class CountedCompleter extends ForkJoinTask<Void> {
+    private static final long serialVersionUID = 5232453752276485070L;
+
+    /** This task's completer, or null if none */
+    final CountedCompleter completer;
+    /** The number of pending tasks until completion */
+    volatile int pending;
+
+    /**
+     * Creates a new CountedCompleter with the given completer
+     * and initial pending count.
+     *
+     * @param completer this tasks completer, or {@code null} if none
+     * @param initialPendingCount the initial pending count
+     */
+    protected CountedCompleter(CountedCompleter completer,
+                               int initialPendingCount) {
+        this.completer = completer;
+        this.pending = initialPendingCount;
+    }
+
+    /**
+     * Creates a new CountedCompleter with the given completer
+     * and an initial pending count of zero.
+     *
+     * @param completer this tasks completer, or {@code null} if none
+     */
+    protected CountedCompleter(CountedCompleter completer) {
+        this.completer = completer;
+    }
+
+    /**
+     * Creates a new CountedCompleter with no completer
+     * and an initial pending count of zero.
+     */
+    protected CountedCompleter() {
+        this.completer = null;
+    }
+
+    /**
+     * The main computation performed by this task.
+     */
+    public abstract void compute();
+
+    /**
+     * Performs an action when method {@link #tryComplete} is invoked
+     * and there are no pending counts, or when the unconditional
+     * method {@link #complete} is invoked.  By default, this method
+     * does nothing.
+     *
+     * @param caller the task invoking this method (which may
+     * be this task itself).
+     */
+    public void onCompletion(CountedCompleter caller) {
+    }
+
+    /**
+     * Performs an action when method {@link #completeExceptionally}
+     * is invoked or method {@link #compute} throws an exception, and
+     * this task has not otherwise already completed normally. On
+     * entry to this method, this task {@link
+     * ForkJoinTask#isCompletedAbnormally}.  The return value of this
+     * method controls further propagation: If {@code true} and this
+     * task has a completer, then this completer is also completed
+     * exceptionally.  The default implementation of this method does
+     * nothing except return {@code true}.
+     *
+     * @param ex the exception
+     * @param caller the task invoking this method (which may
+     * be this task itself).
+     * @return true if this exception should be propagated to this
+     * tasks completer, if one exists.
+     */
+    public boolean onExceptionalCompletion(Throwable ex, CountedCompleter caller) {
+        return true;
+    }
+
+    /**
+     * Returns the completer established in this task's constructor,
+     * or {@code null} if none.
+     *
+     * @return the completer
+     */
+    public final CountedCompleter getCompleter() {
+        return completer;
+    }
+
+    /**
+     * Returns the current pending count.
+     *
+     * @return the current pending count
+     */
+    public final int getPendingCount() {
+        return pending;
+    }
+
+    /**
+     * Sets the pending count to the given value.
+     *
+     * @param count the count
+     */
+    public final void setPendingCount(int count) {
+        pending = count;
+    }
+
+    /**
+     * Adds (atomically) the given value to the pending count.
+     *
+     * @param delta the value to add
+     */
+    public final void addToPendingCount(int delta) {
+        int c; // note: can replace with intrinsic in jdk8
+        do {} while (!U.compareAndSwapInt(this, PENDING, c = pending, c+delta));
+    }
+
+    /**
+     * Sets (atomically) the pending count to the given count only if
+     * it currently holds the given expected value.
+     *
+     * @param expected the expected value
+     * @param count the new value
+     * @return true is successful
+     */
+    public final boolean compareAndSetPendingCount(int expected, int count) {
+        return U.compareAndSwapInt(this, PENDING, expected, count);
+    }
+
+    /**
+     * If the pending count is nonzero, decrements the count;
+     * otherwise invokes {@link #onCompletion} and then similarly
+     * tries to complete this task's completer, if one exists,
+     * else marks this task as complete.
+     */
+    public final void tryComplete() {
+        CountedCompleter a = this, s = a;
+        for (int c;;) {
+            if ((c = a.pending) == 0) {
+                a.onCompletion(s);
+                if ((a = (s = a).completer) == null) {
+                    s.quietlyComplete();
+                    return;
+                }
+            }
+            else if (U.compareAndSwapInt(a, PENDING, c, c - 1))
+                return;
+        }
+    }
+
+    /**
+     * Regardless of pending count, invokes {@link #onCompletion},
+     * marks this task as complete with a {@code null} return value,
+     * and further triggers {@link #tryComplete} on this task's
+     * completer, if one exists. This method may be useful when
+     * forcing completion as soon as any one (versus all) of several
+     * subtask results are obtained.
+     *
+     * @param mustBeNull the {@code null} completion value
+     */
+    public void complete(Void mustBeNull) {
+        CountedCompleter p;
+        onCompletion(this);
+        quietlyComplete();
+        if ((p = completer) != null)
+            p.tryComplete();
+    }
+
+    /**
+     * Support for FJT exception propagation
+     */
+    void internalPropagateException(Throwable ex) {
+        CountedCompleter a = this, s = a;
+        while (a.onExceptionalCompletion(ex, s) &&
+               (a = (s = a).completer) != null && a.status >= 0)
+            a.recordExceptionalCompletion(ex);
+    }
+
+    /**
+     * Implements execution conventions for CountedCompleters
+     */
+    protected final boolean exec() {
+        compute();
+        return false;
+    }
+
+    /**
+     * Always returns {@code null}.
+     *
+     * @return {@code null} always
+     */
+    public final Void getRawResult() { return null; }
+
+    /**
+     * Requires null completion value.
+     */
+    protected final void setRawResult(Void mustBeNull) { }
+
+
+    // Unsafe mechanics
+    private static final sun.misc.Unsafe U;
+    private static final long PENDING;
+    static {
+        try {
+            U = sun.misc.Unsafe.getUnsafe();
+            PENDING = U.objectFieldOffset
+                (CountedCompleter.class.getDeclaredField("pending"));
+        } catch (Exception e) {
+            throw new Error(e);
+        }
+    }
+}

--- a/src/share/classes/java/util/concurrent/ForkJoinPool.java	Mon Aug 20 17:14:26 2012 -0700
+++ b/src/share/classes/java/util/concurrent/ForkJoinPool.java	Wed Aug 22 18:22:03 2012 -0700
@@ -48,10 +48,9 @@
 import java.util.concurrent.RejectedExecutionException;
 import java.util.concurrent.RunnableFuture;
 import java.util.concurrent.TimeUnit;
-import java.util.concurrent.TimeoutException;
 import java.util.concurrent.atomic.AtomicInteger;
-import java.util.concurrent.locks.LockSupport;
-import java.util.concurrent.locks.ReentrantLock;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.locks.AbstractQueuedSynchronizer;
 import java.util.concurrent.locks.Condition;
 
 /**
@@ -63,12 +62,14 @@
  * <p>A {@code ForkJoinPool} differs from other kinds of {@link
  * ExecutorService} mainly by virtue of employing
  * <em>work-stealing</em>: all threads in the pool attempt to find and
- * execute subtasks created by other active tasks (eventually blocking
- * waiting for work if none exist). This enables efficient processing
- * when most tasks spawn other subtasks (as do most {@code
- * ForkJoinTask}s). When setting <em>asyncMode</em> to true in
- * constructors, {@code ForkJoinPool}s may also be appropriate for use
- * with event-style tasks that are never joined.
+ * execute tasks submitted to the pool and/or created by other active
+ * tasks (eventually blocking waiting for work if none exist). This
+ * enables efficient processing when most tasks spawn other subtasks
+ * (as do most {@code ForkJoinTask}s), as well as when many small
+ * tasks are submitted to the pool from external clients.  Especially
+ * when setting <em>asyncMode</em> to true in constructors, {@code
+ * ForkJoinPool}s may also be appropriate for use with event-style
+ * tasks that are never joined.
  *
  * <p>A {@code ForkJoinPool} is constructed with a given target
  * parallelism level; by default, equal to the number of available
@@ -88,15 +89,16 @@
  * convenient form for informal monitoring.
  *
  * <p> As is the case with other ExecutorServices, there are three
- * main task execution methods summarized in the following
- * table. These are designed to be used by clients not already engaged
- * in fork/join computations in the current pool.  The main forms of
- * these methods accept instances of {@code ForkJoinTask}, but
- * overloaded forms also allow mixed execution of plain {@code
+ * main task execution methods summarized in the following table.
+ * These are designed to be used primarily by clients not already
+ * engaged in fork/join computations in the current pool.  The main
+ * forms of these methods accept instances of {@code ForkJoinTask},
+ * but overloaded forms also allow mixed execution of plain {@code
  * Runnable}- or {@code Callable}- based activities as well.  However,
- * tasks that are already executing in a pool should normally
- * <em>NOT</em> use these pool execution methods, but instead use the
- * within-computation forms listed in the table.
+ * tasks that are already executing in a pool should normally instead
+ * use the within-computation forms listed in the table unless using
+ * async event-style tasks that are not usually joined, in which case
+ * there is little difference among choice of methods.
  *
  * <table BORDER CELLPADDING=3 CELLSPACING=1>
  *  <tr>
@@ -131,13 +133,12 @@
  * daemon} mode, there is typically no need to explicitly {@link
  * #shutdown} such a pool upon program exit.
  *
- * <pre>
+ *  <pre> {@code
  * static final ForkJoinPool mainPool = new ForkJoinPool();
  * ...
  * public void sort(long[] array) {
  *   mainPool.invoke(new SortTask(array, 0, array.length));
- * }
- * </pre>
+ * }}</pre>
  *
  * <p><b>Implementation notes</b>: This implementation restricts the
  * maximum number of running threads to 32767. Attempts to create
@@ -156,108 +157,196 @@
     /*
      * Implementation Overview
      *
-     * This class provides the central bookkeeping and control for a
-     * set of worker threads: Submissions from non-FJ threads enter
-     * into a submission queue. Workers take these tasks and typically
-     * split them into subtasks that may be stolen by other workers.
-     * Preference rules give first priority to processing tasks from
-     * their own queues (LIFO or FIFO, depending on mode), then to
-     * randomized FIFO steals of tasks in other worker queues, and
-     * lastly to new submissions.
+     * This class and its nested classes provide the main
+     * functionality and control for a set of worker threads:
+     * Submissions from non-FJ threads enter into submission queues.
+     * Workers take these tasks and typically split them into subtasks
+     * that may be stolen by other workers.  Preference rules give
+     * first priority to processing tasks from their own queues (LIFO
+     * or FIFO, depending on mode), then to randomized FIFO steals of
+     * tasks in other queues.
+     *
+     * WorkQueues
+     * ==========
+     *
+     * Most operations occur within work-stealing queues (in nested
+     * class WorkQueue).  These are special forms of Deques that
+     * support only three of the four possible end-operations -- push,
+     * pop, and poll (aka steal), under the further constraints that
+     * push and pop are called only from the owning thread (or, as
+     * extended here, under a lock), while poll may be called from
+     * other threads.  (If you are unfamiliar with them, you probably
+     * want to read Herlihy and Shavit's book "The Art of
+     * Multiprocessor programming", chapter 16 describing these in
+     * more detail before proceeding.)  The main work-stealing queue
+     * design is roughly similar to those in the papers "Dynamic
+     * Circular Work-Stealing Deque" by Chase and Lev, SPAA 2005
+     * (http://research.sun.com/scalable/pubs/index.html) and
+     * "Idempotent work stealing" by Michael, Saraswat, and Vechev,
+     * PPoPP 2009 (http://portal.acm.org/citation.cfm?id=1504186).
+     * The main differences ultimately stem from GC requirements that
+     * we null out taken slots as soon as we can, to maintain as small
+     * a footprint as possible even in programs generating huge
+     * numbers of tasks. To accomplish this, we shift the CAS
+     * arbitrating pop vs poll (steal) from being on the indices
+     * ("base" and "top") to the slots themselves.  So, both a
+     * successful pop and poll mainly entail a CAS of a slot from
+     * non-null to null.  Because we rely on CASes of references, we
+     * do not need tag bits on base or top.  They are simple ints as
+     * used in any circular array-based queue (see for example
+     * ArrayDeque).  Updates to the indices must still be ordered in a
+     * way that guarantees that top == base means the queue is empty,
+     * but otherwise may err on the side of possibly making the queue
+     * appear nonempty when a push, pop, or poll have not fully
+     * committed. Note that this means that the poll operation,
+     * considered individually, is not wait-free. One thief cannot
+     * successfully continue until another in-progress one (or, if
+     * previously empty, a push) completes.  However, in the
+     * aggregate, we ensure at least probabilistic non-blockingness.
+     * If an attempted steal fails, a thief always chooses a different
+     * random victim target to try next. So, in order for one thief to
+     * progress, it suffices for any in-progress poll or new push on
+     * any empty queue to complete. (This is why we normally use
+     * method pollAt and its variants that try once at the apparent
+     * base index, else consider alternative actions, rather than
+     * method poll.)
+     *
+     * This approach also enables support of a user mode in which local
+     * task processing is in FIFO, not LIFO order, simply by using
+     * poll rather than pop.  This can be useful in message-passing
+     * frameworks in which tasks are never joined.  However neither
+     * mode considers affinities, loads, cache localities, etc, so
+     * rarely provide the best possible performance on a given
+     * machine, but portably provide good throughput by averaging over
+     * these factors.  (Further, even if we did try to use such
+     * information, we do not usually have a basis for exploiting it.
+     * For example, some sets of tasks profit from cache affinities,
+     * but others are harmed by cache pollution effects.)
+     *
+     * WorkQueues are also used in a similar way for tasks submitted
+     * to the pool. We cannot mix these tasks in the same queues used
+     * for work-stealing (this would contaminate lifo/fifo
+     * processing). Instead, we loosely associate submission queues
+     * with submitting threads, using a form of hashing.  The
+     * ThreadLocal Submitter class contains a value initially used as
+     * a hash code for choosing existing queues, but may be randomly
+     * repositioned upon contention with other submitters.  In
+     * essence, submitters act like workers except that they never
+     * take tasks, and they are multiplexed on to a finite number of
+     * shared work queues. However, classes are set up so that future
+     * extensions could allow submitters to optionally help perform
+     * tasks as well. Insertion of tasks in shared mode requires a
+     * lock (mainly to protect in the case of resizing) but we use
+     * only a simple spinlock (using bits in field runState), because
+     * submitters encountering a busy queue move on to try or create
+     * other queues -- they block only when creating and registering
+     * new queues.
+     *
+     * Management
+     * ==========
      *
      * The main throughput advantages of work-stealing stem from
      * decentralized control -- workers mostly take tasks from
      * themselves or each other. We cannot negate this in the
      * implementation of other management responsibilities. The main
      * tactic for avoiding bottlenecks is packing nearly all
-     * essentially atomic control state into a single 64bit volatile
-     * variable ("ctl"). This variable is read on the order of 10-100
-     * times as often as it is modified (always via CAS). (There is
-     * some additional control state, for example variable "shutdown"
-     * for which we can cope with uncoordinated updates.)  This
-     * streamlines synchronization and control at the expense of messy
-     * constructions needed to repack status bits upon updates.
-     * Updates tend not to contend with each other except during
-     * bursts while submitted tasks begin or end.  In some cases when
-     * they do contend, threads can instead do something else
-     * (usually, scan for tasks) until contention subsides.
+     * essentially atomic control state into two volatile variables
+     * that are by far most often read (not written) as status and
+     * consistency checks.
+     *
+     * Field "ctl" contains 64 bits holding all the information needed
+     * to atomically decide to add, inactivate, enqueue (on an event
+     * queue), dequeue, and/or re-activate workers.  To enable this
+     * packing, we restrict maximum parallelism to (1<<15)-1 (which is
+     * far in excess of normal operating range) to allow ids, counts,
+     * and their negations (used for thresholding) to fit into 16bit
+     * fields.
      *
-     * To enable packing, we restrict maximum parallelism to (1<<15)-1
-     * (which is far in excess of normal operating range) to allow
-     * ids, counts, and their negations (used for thresholding) to fit
-     * into 16bit fields.
+     * Field "runState" contains 32 bits needed to register and
+     * deregister WorkQueues, as well as to enable shutdown. It is
+     * only modified under a lock (normally briefly held, but
+     * occasionally protecting allocations and resizings) but even
+     * when locked remains available to check consistency.
      *
-     * Recording Workers.  Workers are recorded in the "workers" array
-     * that is created upon pool construction and expanded if (rarely)
-     * necessary.  This is an array as opposed to some other data
-     * structure to support index-based random steals by workers.
-     * Updates to the array recording new workers and unrecording
-     * terminated ones are protected from each other by a seqLock
-     * (scanGuard) but the array is otherwise concurrently readable,
-     * and accessed directly by workers. To simplify index-based
+     * Recording WorkQueues.  WorkQueues are recorded in the
+     * "workQueues" array that is created upon pool construction and
+     * expanded if necessary.  Updates to the array while recording
+     * new workers and unrecording terminated ones are protected from
+     * each other by a lock but the array is otherwise concurrently
+     * readable, and accessed directly.  To simplify index-based
      * operations, the array size is always a power of two, and all
-     * readers must tolerate null slots. To avoid flailing during
-     * start-up, the array is presized to hold twice #parallelism
-     * workers (which is unlikely to need further resizing during
-     * execution). But to avoid dealing with so many null slots,
-     * variable scanGuard includes a mask for the nearest power of two
-     * that contains all current workers.  All worker thread creation
-     * is on-demand, triggered by task submissions, replacement of
-     * terminated workers, and/or compensation for blocked
-     * workers. However, all other support code is set up to work with
-     * other policies.  To ensure that we do not hold on to worker
-     * references that would prevent GC, ALL accesses to workers are
-     * via indices into the workers array (which is one source of some
-     * of the messy code constructions here). In essence, the workers
-     * array serves as a weak reference mechanism. Thus for example
-     * the wait queue field of ctl stores worker indices, not worker
-     * references.  Access to the workers in associated methods (for
-     * example signalWork) must both index-check and null-check the
-     * IDs. All such accesses ignore bad IDs by returning out early
-     * from what they are doing, since this can only be associated
-     * with termination, in which case it is OK to give up.
+     * readers must tolerate null slots. Shared (submission) queues
+     * are at even indices, worker queues at odd indices. Grouping
+     * them together in this way simplifies and speeds up task
+     * scanning.
      *
-     * All uses of the workers array, as well as queue arrays, check
-     * that the array is non-null (even if previously non-null). This
-     * allows nulling during termination, which is currently not
-     * necessary, but remains an option for resource-revocation-based
-     * shutdown schemes.
+     * All worker thread creation is on-demand, triggered by task
+     * submissions, replacement of terminated workers, and/or
+     * compensation for blocked workers. However, all other support
+     * code is set up to work with other policies.  To ensure that we
+     * do not hold on to worker references that would prevent GC, ALL
+     * accesses to workQueues are via indices into the workQueues
+     * array (which is one source of some of the messy code
+     * constructions here). In essence, the workQueues array serves as
+     * a weak reference mechanism. Thus for example the wait queue
+     * field of ctl stores indices, not references.  Access to the
+     * workQueues in associated methods (for example signalWork) must
+     * both index-check and null-check the IDs. All such accesses
+     * ignore bad IDs by returning out early from what they are doing,
+     * since this can only be associated with termination, in which
+     * case it is OK to give up.  All uses of the workQueues array
+     * also check that it is non-null (even if previously
+     * non-null). This allows nulling during termination, which is
+     * currently not necessary, but remains an option for
+     * resource-revocation-based shutdown schemes. It also helps
+     * reduce JIT issuance of uncommon-trap code, which tends to
+     * unnecessarily complicate control flow in some methods.
      *
-     * Wait Queuing. Unlike HPC work-stealing frameworks, we cannot
+     * Event Queuing. Unlike HPC work-stealing frameworks, we cannot
      * let workers spin indefinitely scanning for tasks when none can
      * be found immediately, and we cannot start/resume workers unless
      * there appear to be tasks available.  On the other hand, we must
      * quickly prod them into action when new tasks are submitted or
-     * generated.  We park/unpark workers after placing in an event
-     * wait queue when they cannot find work. This "queue" is actually
-     * a simple Treiber stack, headed by the "id" field of ctl, plus a
-     * 15bit counter value to both wake up waiters (by advancing their
-     * count) and avoid ABA effects. Successors are held in worker
-     * field "nextWait".  Queuing deals with several intrinsic races,
-     * mainly that a task-producing thread can miss seeing (and
+     * generated. In many usages, ramp-up time to activate workers is
+     * the main limiting factor in overall performance (this is
+     * compounded at program start-up by JIT compilation and
+     * allocation). So we try to streamline this as much as possible.
+     * We park/unpark workers after placing in an event wait queue
+     * when they cannot find work. This "queue" is actually a simple
+     * Treiber stack, headed by the "id" field of ctl, plus a 15bit
+     * counter value (that reflects the number of times a worker has
+     * been inactivated) to avoid ABA effects (we need only as many
+     * version numbers as worker threads). Successors are held in
+     * field WorkQueue.nextWait.  Queuing deals with several intrinsic
+     * races, mainly that a task-producing thread can miss seeing (and
      * signalling) another thread that gave up looking for work but
      * has not yet entered the wait queue. We solve this by requiring
-     * a full sweep of all workers both before (in scan()) and after
-     * (in tryAwaitWork()) a newly waiting worker is added to the wait
-     * queue. During a rescan, the worker might release some other
-     * queued worker rather than itself, which has the same net
-     * effect. Because enqueued workers may actually be rescanning
-     * rather than waiting, we set and clear the "parked" field of
-     * ForkJoinWorkerThread to reduce unnecessary calls to unpark.
-     * (Use of the parked field requires a secondary recheck to avoid
-     * missed signals.)
+     * a full sweep of all workers (via repeated calls to method
+     * scan()) both before and after a newly waiting worker is added
+     * to the wait queue. During a rescan, the worker might release
+     * some other queued worker rather than itself, which has the same
+     * net effect. Because enqueued workers may actually be rescanning
+     * rather than waiting, we set and clear the "parker" field of
+     * WorkQueues to reduce unnecessary calls to unpark.  (This
+     * requires a secondary recheck to avoid missed signals.)  Note
+     * the unusual conventions about Thread.interrupts surrounding
+     * parking and other blocking: Because interrupts are used solely
+     * to alert threads to check termination, which is checked anyway
+     * upon blocking, we clear status (using Thread.interrupted)
+     * before any call to park, so that park does not immediately
+     * return due to status being set via some other unrelated call to
+     * interrupt in user code.
      *
      * Signalling.  We create or wake up workers only when there
      * appears to be at least one task they might be able to find and
      * execute.  When a submission is added or another worker adds a
-     * task to a queue that previously had two or fewer tasks, they
+     * task to a queue that previously had fewer than two tasks, they
      * signal waiting workers (or trigger creation of new ones if
      * fewer than the given parallelism level -- see signalWork).
-     * These primary signals are buttressed by signals during rescans
-     * as well as those performed when a worker steals a task and
-     * notices that there are more tasks too; together these cover the
-     * signals needed in cases when more than two tasks are pushed
-     * but untaken.
+     * These primary signals are buttressed by signals during rescans;
+     * together these cover the signals needed in cases when more
+     * tasks are pushed but untaken, and improve performance compared
+     * to having one thread wake up all workers.
      *
      * Trimming workers. To release resources after periods of lack of
      * use, a worker starting to wait when the pool is quiescent will
@@ -265,105 +354,158 @@
      * SHRINK_RATE nanosecs. This will slowly propagate, eventually
      * terminating all workers after long periods of non-use.
      *
-     * Submissions. External submissions are maintained in an
-     * array-based queue that is structured identically to
-     * ForkJoinWorkerThread queues except for the use of
-     * submissionLock in method addSubmission. Unlike the case for
-     * worker queues, multiple external threads can add new
-     * submissions, so adding requires a lock.
+     * Shutdown and Termination. A call to shutdownNow atomically sets
+     * a runState bit and then (non-atomically) sets each worker's
+     * runState status, cancels all unprocessed tasks, and wakes up
+     * all waiting workers.  Detecting whether termination should
+     * commence after a non-abrupt shutdown() call requires more work
+     * and bookkeeping. We need consensus about quiescence (i.e., that
+     * there is no more work). The active count provides a primary
+     * indication but non-abrupt shutdown still requires a rechecking
+     * scan for any workers that are inactive but not queued.
      *
-     * Compensation. Beyond work-stealing support and lifecycle
-     * control, the main responsibility of this framework is to take
-     * actions when one worker is waiting to join a task stolen (or
-     * always held by) another.  Because we are multiplexing many
-     * tasks on to a pool of workers, we can't just let them block (as
-     * in Thread.join).  We also cannot just reassign the joiner's
-     * run-time stack with another and replace it later, which would
-     * be a form of "continuation", that even if possible is not
-     * necessarily a good idea since we sometimes need both an
-     * unblocked task and its continuation to progress. Instead we
-     * combine two tactics:
+     * Joining Tasks
+     * =============
+     *
+     * Any of several actions may be taken when one worker is waiting
+     * to join a task stolen (or always held) by another.  Because we
+     * are multiplexing many tasks on to a pool of workers, we can't
+     * just let them block (as in Thread.join).  We also cannot just
+     * reassign the joiner's run-time stack with another and replace
+     * it later, which would be a form of "continuation", that even if
+     * possible is not necessarily a good idea since we sometimes need
+     * both an unblocked task and its continuation to progress.
+     * Instead we combine two tactics:
      *
      *   Helping: Arranging for the joiner to execute some task that it
-     *      would be running if the steal had not occurred.  Method
-     *      ForkJoinWorkerThread.joinTask tracks joining->stealing
-     *      links to try to find such a task.
+     *      would be running if the steal had not occurred.
      *
      *   Compensating: Unless there are already enough live threads,
-     *      method tryPreBlock() may create or re-activate a spare
-     *      thread to compensate for blocked joiners until they
-     *      unblock.
+     *      method tryCompensate() may create or re-activate a spare
+     *      thread to compensate for blocked joiners until they unblock.
+     *
+     * A third form (implemented in tryRemoveAndExec and
+     * tryPollForAndExec) amounts to helping a hypothetical
+     * compensator: If we can readily tell that a possible action of a
+     * compensator is to steal and execute the task being joined, the
+     * joining thread can do so directly, without the need for a
+     * compensation thread (although at the expense of larger run-time
+     * stacks, but the tradeoff is typically worthwhile).
      *
      * The ManagedBlocker extension API can't use helping so relies
      * only on compensation in method awaitBlocker.
      *
+     * The algorithm in tryHelpStealer entails a form of "linear"
+     * helping: Each worker records (in field currentSteal) the most
+     * recent task it stole from some other worker. Plus, it records
+     * (in field currentJoin) the task it is currently actively
+     * joining. Method tryHelpStealer uses these markers to try to
+     * find a worker to help (i.e., steal back a task from and execute
+     * it) that could hasten completion of the actively joined task.
+     * In essence, the joiner executes a task that would be on its own
+     * local deque had the to-be-joined task not been stolen. This may
+     * be seen as a conservative variant of the approach in Wagner &
+     * Calder "Leapfrogging: a portable technique for implementing
+     * efficient futures" SIGPLAN Notices, 1993
+     * (http://portal.acm.org/citation.cfm?id=155354). It differs in
+     * that: (1) We only maintain dependency links across workers upon
+     * steals, rather than use per-task bookkeeping.  This sometimes
+     * requires a linear scan of workQueues array to locate stealers,
+     * but often doesn't because stealers leave hints (that may become
+     * stale/wrong) of where to locate them.  A stealHint is only a
+     * hint because a worker might have had multiple steals and the
+     * hint records only one of them (usually the most current).
+     * Hinting isolates cost to when it is needed, rather than adding
+     * to per-task overhead.  (2) It is "shallow", ignoring nesting
+     * and potentially cyclic mutual steals.  (3) It is intentionally
+     * racy: field currentJoin is updated only while actively joining,
+     * which means that we miss links in the chain during long-lived
+     * tasks, GC stalls etc (which is OK since blocking in such cases
+     * is usually a good idea).  (4) We bound the number of attempts
+     * to find work (see MAX_HELP) and fall back to suspending the
+     * worker and if necessary replacing it with another.
+     *
      * It is impossible to keep exactly the target parallelism number
      * of threads running at any given time.  Determining the
      * existence of conservatively safe helping targets, the
      * availability of already-created spares, and the apparent need
-     * to create new spares are all racy and require heuristic
-     * guidance, so we rely on multiple retries of each.  Currently,
-     * in keeping with on-demand signalling policy, we compensate only
-     * if blocking would leave less than one active (non-waiting,
-     * non-blocked) worker. Additionally, to avoid some false alarms
-     * due to GC, lagging counters, system activity, etc, compensated
-     * blocking for joins is only attempted after rechecks stabilize
-     * (retries are interspersed with Thread.yield, for good
-     * citizenship).  The variable blockedCount, incremented before
-     * blocking and decremented after, is sometimes needed to
-     * distinguish cases of waiting for work vs blocking on joins or
-     * other managed sync. Both cases are equivalent for most pool
-     * control, so we can update non-atomically. (Additionally,
-     * contention on blockedCount alleviates some contention on ctl).
-     *
-     * Shutdown and Termination. A call to shutdownNow atomically sets
-     * the ctl stop bit and then (non-atomically) sets each workers
-     * "terminate" status, cancels all unprocessed tasks, and wakes up
-     * all waiting workers.  Detecting whether termination should
-     * commence after a non-abrupt shutdown() call requires more work
-     * and bookkeeping. We need consensus about quiesence (i.e., that
-     * there is no more work) which is reflected in active counts so
-     * long as there are no current blockers, as well as possible
-     * re-evaluations during independent changes in blocking or
-     * quiescing workers.
+     * to create new spares are all racy, so we rely on multiple
+     * retries of each.  Compensation in the apparent absence of
+     * helping opportunities is challenging to control on JVMs, where
+     * GC and other activities can stall progress of tasks that in
+     * turn stall out many other dependent tasks, without us being
+     * able to determine whether they will ever require compensation.
+     * Even though work-stealing otherwise encounters little
+     * degradation in the presence of more threads than cores,
+     * aggressively adding new threads in such cases entails risk of
+     * unwanted positive feedback control loops in which more threads
+     * cause more dependent stalls (as well as delayed progress of
+     * unblocked threads to the point that we know they are available)
+     * leading to more situations requiring more threads, and so
+     * on. This aspect of control can be seen as an (analytically
+     * intractable) game with an opponent that may choose the worst
+     * (for us) active thread to stall at any time.  We take several
+     * precautions to bound losses (and thus bound gains), mainly in
+     * methods tryCompensate and awaitJoin: (1) We only try
+     * compensation after attempting enough helping steps (measured
+     * via counting and timing) that we have already consumed the
+     * estimated cost of creating and activating a new thread.  (2) We
+     * allow up to 50% of threads to be blocked before initially
+     * adding any others, and unless completely saturated, check that
+     * some work is available for a new worker before adding. Also, we
+     * create up to only 50% more threads until entering a mode that
+     * only adds a thread if all others are possibly blocked.  All
+     * together, this means that we might be half as fast to react,
+     * and create half as many threads as possible in the ideal case,
+     * but present vastly fewer anomalies in all other cases compared
+     * to both more aggressive and more conservative alternatives.
      *
      * Style notes: There is a lot of representation-level coupling
      * among classes ForkJoinPool, ForkJoinWorkerThread, and
-     * ForkJoinTask.  Most fields of ForkJoinWorkerThread maintain
-     * data structures managed by ForkJoinPool, so are directly
-     * accessed.  Conversely we allow access to "workers" array by
-     * workers, and direct access to ForkJoinTask.status by both
-     * ForkJoinPool and ForkJoinWorkerThread.  There is little point
-     * trying to reduce this, since any associated future changes in
-     * representations will need to be accompanied by algorithmic
-     * changes anyway. All together, these low-level implementation
-     * choices produce as much as a factor of 4 performance
-     * improvement compared to naive implementations, and enable the
-     * processing of billions of tasks per second, at the expense of
-     * some ugliness.
+     * ForkJoinTask.  The fields of WorkQueue maintain data structures
+     * managed by ForkJoinPool, so are directly accessed.  There is
+     * little point trying to reduce this, since any associated future
+     * changes in representations will need to be accompanied by
+     * algorithmic changes anyway. Several methods intrinsically
+     * sprawl because they must accumulate sets of consistent reads of
+     * volatiles held in local variables.  Methods signalWork() and
+     * scan() are the main bottlenecks, so are especially heavily
+     * micro-optimized/mangled.  There are lots of inline assignments
+     * (of form "while ((local = field) != 0)") which are usually the
+     * simplest way to ensure the required read orderings (which are
+     * sometimes critical). This leads to a "C"-like style of listing
+     * declarations of these locals at the heads of methods or blocks.
+     * There are several occurrences of the unusual "do {} while
+     * (!cas...)"  which is the simplest way to force an update of a
+     * CAS'ed variable. There are also other coding oddities that help
+     * some methods perform reasonably even when interpreted (not
+     * compiled).
      *
-     * Methods signalWork() and scan() are the main bottlenecks so are
-     * especially heavily micro-optimized/mangled.  There are lots of
-     * inline assignments (of form "while ((local = field) != 0)")
-     * which are usually the simplest way to ensure the required read
-     * orderings (which are sometimes critical). This leads to a
-     * "C"-like style of listing declarations of these locals at the
-     * heads of methods or blocks.  There are several occurrences of
-     * the unusual "do {} while (!cas...)"  which is the simplest way
-     * to force an update of a CAS'ed variable. There are also other
-     * coding oddities that help some methods perform reasonably even
-     * when interpreted (not compiled).
-     *
-     * The order of declarations in this file is: (1) declarations of
-     * statics (2) fields (along with constants used when unpacking
-     * some of them), listed in an order that tends to reduce
-     * contention among them a bit under most JVMs.  (3) internal
-     * control methods (4) callbacks and other support for
-     * ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
-     * methods (plus a few little helpers). (6) static block
-     * initializing all statics in a minimally dependent order.
+     * The order of declarations in this file is:
+     * (1) Static utility functions
+     * (2) Nested (static) classes
+     * (3) Static fields
+     * (4) Fields, along with constants used when unpacking some of them
+     * (5) Internal control methods
+     * (6) Callbacks and other support for ForkJoinTask methods
+     * (7) Exported methods
+     * (8) Static block initializing statics in minimally dependent order
      */
 
+    // Static utilities
+
+    /**
+     * If there is a security manager, makes sure caller has
+     * permission to modify threads.
+     */
+    private static void checkPermission() {
+        SecurityManager security = System.getSecurityManager();
+        if (security != null)
+            security.checkPermission(modifyThreadPermission);
+    }
+
+    // Nested classes
+
     /**
      * Factory for creating new {@link ForkJoinWorkerThread}s.
      * A {@code ForkJoinWorkerThreadFactory} must be defined and used
@@ -392,6 +534,582 @@
     }
 
     /**
+     * A simple non-reentrant lock used for exclusion when managing
+     * queues and workers. We use a custom lock so that we can readily
+     * probe lock state in constructions that check among alternative
+     * actions. The lock is normally only very briefly held, and
+     * sometimes treated as a spinlock, but other usages block to
+     * reduce overall contention in those cases where locked code
+     * bodies perform allocation/resizing.
+     */
+    static final class Mutex extends AbstractQueuedSynchronizer {
+        public final boolean tryAcquire(int ignore) {
+            return compareAndSetState(0, 1);
+        }
+        public final boolean tryRelease(int ignore) {
+            setState(0);
+            return true;
+        }
+        public final void lock() { acquire(0); }
+        public final void unlock() { release(0); }
+        public final boolean isHeldExclusively() { return getState() == 1; }
+        public final Condition newCondition() { return new ConditionObject(); }
+    }
+
+    /**
+     * Class for artificial tasks that are used to replace the target
+     * of local joins if they are removed from an interior queue slot
+     * in WorkQueue.tryRemoveAndExec. We don't need the proxy to
+     * actually do anything beyond having a unique identity.
+     */
+    static final class EmptyTask extends ForkJoinTask<Void> {
+        EmptyTask() { status = ForkJoinTask.NORMAL; } // force done
+        public final Void getRawResult() { return null; }
+        public final void setRawResult(Void x) {}
+        public final boolean exec() { return true; }
+    }
+
+    /**
+     * Queues supporting work-stealing as well as external task
+     * submission. See above for main rationale and algorithms.
+     * Implementation relies heavily on "Unsafe" intrinsics
+     * and selective use of "volatile":
+     *
+     * Field "base" is the index (mod array.length) of the least valid
+     * queue slot, which is always the next position to steal (poll)
+     * from if nonempty. Reads and writes require volatile orderings
+     * but not CAS, because updates are only performed after slot
+     * CASes.
+     *
+     * Field "top" is the index (mod array.length) of the next queue
+     * slot to push to or pop from. It is written only by owner thread
+     * for push, or under lock for trySharedPush, and accessed by
+     * other threads only after reading (volatile) base.  Both top and
+     * base are allowed to wrap around on overflow, but (top - base)
+     * (or more commonly -(base - top) to force volatile read of base
+     * before top) still estimates size.
+     *
+     * The array slots are read and written using the emulation of
+     * volatiles/atomics provided by Unsafe. Insertions must in
+     * general use putOrderedObject as a form of releasing store to
+     * ensure that all writes to the task object are ordered before
+     * its publication in the queue. (Although we can avoid one case
+     * of this when locked in trySharedPush.) All removals entail a
+     * CAS to null.  The array is always a power of two. To ensure
+     * safety of Unsafe array operations, all accesses perform
+     * explicit null checks and implicit bounds checks via
+     * power-of-two masking.
+     *
+     * In addition to basic queuing support, this class contains
+     * fields described elsewhere to control execution. It turns out
+     * to work better memory-layout-wise to include them in this
+     * class rather than a separate class.
+     *
+     * Performance on most platforms is very sensitive to placement of
+     * instances of both WorkQueues and their arrays -- we absolutely
+     * do not want multiple WorkQueue instances or multiple queue
+     * arrays sharing cache lines. (It would be best for queue objects
+     * and their arrays to share, but there is nothing available to
+     * help arrange that).  Unfortunately, because they are recorded
+     * in a common array, WorkQueue instances are often moved to be
+     * adjacent by garbage collectors. To reduce impact, we use field
+     * padding that works OK on common platforms; this effectively
+     * trades off slightly slower average field access for the sake of
+     * avoiding really bad worst-case access. (Until better JVM
+     * support is in place, this padding is dependent on transient
+     * properties of JVM field layout rules.)  We also take care in
+     * allocating, sizing and resizing the array. Non-shared queue
+     * arrays are initialized (via method growArray) by workers before
+     * use. Others are allocated on first use.
+     */
+    static final class WorkQueue {
+        /**
+         * Capacity of work-stealing queue array upon initialization.
+         * Must be a power of two; at least 4, but should be larger to
+         * reduce or eliminate cacheline sharing among queues.
+         * Currently, it is much larger, as a partial workaround for
+         * the fact that JVMs often place arrays in locations that
+         * share GC bookkeeping (especially cardmarks) such that
+         * per-write accesses encounter serious memory contention.
+         */
+        static final int INITIAL_QUEUE_CAPACITY = 1 << 13;
+
+        /**
+         * Maximum size for queue arrays. Must be a power of two less
+         * than or equal to 1 << (31 - width of array entry) to ensure
+         * lack of wraparound of index calculations, but defined to a
+         * value a bit less than this to help users trap runaway
+         * programs before saturating systems.
+         */
+        static final int MAXIMUM_QUEUE_CAPACITY = 1 << 26; // 64M
+
+        volatile long totalSteals; // cumulative number of steals
+        int seed;                  // for random scanning; initialize nonzero
+        volatile int eventCount;   // encoded inactivation count; < 0 if inactive
+        int nextWait;              // encoded record of next event waiter
+        int rescans;               // remaining scans until block
+        int nsteals;               // top-level task executions since last idle
+        final int mode;            // lifo, fifo, or shared
+        int poolIndex;             // index of this queue in pool (or 0)
+        int stealHint;             // index of most recent known stealer
+        volatile int runState;     // 1: locked, -1: terminate; else 0
+        volatile int base;         // index of next slot for poll
+        int top;                   // index of next slot for push
+        ForkJoinTask<?>[] array;   // the elements (initially unallocated)
+        final ForkJoinPool pool;   // the containing pool (may be null)
+        final ForkJoinWorkerThread owner; // owning thread or null if shared
+        volatile Thread parker;    // == owner during call to park; else null
+        volatile ForkJoinTask<?> currentJoin;  // task being joined in awaitJoin
+        ForkJoinTask<?> currentSteal; // current non-local task being executed
+        // Heuristic padding to ameliorate unfortunate memory placements
+        Object p00, p01, p02, p03, p04, p05, p06, p07;
+        Object p08, p09, p0a, p0b, p0c, p0d, p0e;
+
+        WorkQueue(ForkJoinPool pool, ForkJoinWorkerThread owner, int mode) {
+            this.mode = mode;
+            this.pool = pool;
+            this.owner = owner;
+            // Place indices in the center of array (that is not yet allocated)
+            base = top = INITIAL_QUEUE_CAPACITY >>> 1;
+        }
+
+        /**
+         * Returns the approximate number of tasks in the queue.
+         */
+        final int queueSize() {
+            int n = base - top;       // non-owner callers must read base first
+            return (n >= 0) ? 0 : -n; // ignore transient negative
+        }
+
+        /**
+         * Provides a more accurate estimate of whether this queue has
+         * any tasks than does queueSize, by checking whether a
+         * near-empty queue has at least one unclaimed task.
+         */
+        final boolean isEmpty() {
+            ForkJoinTask<?>[] a; int m, s;
+            int n = base - (s = top);
+            return (n >= 0 ||
+                    (n == -1 &&
+                     ((a = array) == null ||
+                      (m = a.length - 1) < 0 ||
+                      U.getObjectVolatile
+                      (a, ((m & (s - 1)) << ASHIFT) + ABASE) == null)));
+        }
+
+        /**
+         * Pushes a task. Call only by owner in unshared queues.
+         *
+         * @param task the task. Caller must ensure non-null.
+         * @throw RejectedExecutionException if array cannot be resized
+         */
+        final void push(ForkJoinTask<?> task) {
+            ForkJoinTask<?>[] a; ForkJoinPool p;
+            int s = top, m, n;
+            if ((a = array) != null) {    // ignore if queue removed
+                U.putOrderedObject
+                    (a, (((m = a.length - 1) & s) << ASHIFT) + ABASE, task);
+                if ((n = (top = s + 1) - base) <= 2) {
+                    if ((p = pool) != null)
+                        p.signalWork();
+                }
+                else if (n >= m)
+                    growArray(true);
+            }
+        }
+
+        /**
+         * Pushes a task if lock is free and array is either big
+         * enough or can be resized to be big enough.
+         *
+         * @param task the task. Caller must ensure non-null.
+         * @return true if submitted
+         */
+        final boolean trySharedPush(ForkJoinTask<?> task) {
+            boolean submitted = false;
+            if (runState == 0 && U.compareAndSwapInt(this, RUNSTATE, 0, 1)) {
+                ForkJoinTask<?>[] a = array;
+                int s = top;
+                try {
+                    if ((a != null && a.length > s + 1 - base) ||
+                        (a = growArray(false)) != null) { // must presize
+                        int j = (((a.length - 1) & s) << ASHIFT) + ABASE;
+                        U.putObject(a, (long)j, task);    // don't need "ordered"
+                        top = s + 1;
+                        submitted = true;
+                    }
+                } finally {
+                    runState = 0;                         // unlock
+                }
+            }
+            return submitted;
+        }
+
+        /**
+         * Takes next task, if one exists, in LIFO order.  Call only
+         * by owner in unshared queues. (We do not have a shared
+         * version of this method because it is never needed.)
+         */
+        final ForkJoinTask<?> pop() {
+            ForkJoinTask<?>[] a; ForkJoinTask<?> t; int m;
+            if ((a = array) != null && (m = a.length - 1) >= 0) {
+                for (int s; (s = top - 1) - base >= 0;) {
+                    long j = ((m & s) << ASHIFT) + ABASE;
+                    if ((t = (ForkJoinTask<?>)U.getObject(a, j)) == null)
+                        break;
+                    if (U.compareAndSwapObject(a, j, t, null)) {
+                        top = s;
+                        return t;
+                    }
+                }
+            }
+            return null;
+        }
+
+        /**
+         * Takes a task in FIFO order if b is base of queue and a task
+         * can be claimed without contention. Specialized versions
+         * appear in ForkJoinPool methods scan and tryHelpStealer.
+         */
+        final ForkJoinTask<?> pollAt(int b) {
+            ForkJoinTask<?> t; ForkJoinTask<?>[] a;
+            if ((a = array) != null) {
+                int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
+                if ((t = (ForkJoinTask<?>)U.getObjectVolatile(a, j)) != null &&
+                    base == b &&
+                    U.compareAndSwapObject(a, j, t, null)) {
+                    base = b + 1;
+                    return t;
+                }
+            }
+            return null;
+        }
+
+        /**
+         * Takes next task, if one exists, in FIFO order.
+         */
+        final ForkJoinTask<?> poll() {
+            ForkJoinTask<?>[] a; int b; ForkJoinTask<?> t;
+            while ((b = base) - top < 0 && (a = array) != null) {
+                int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
+                t = (ForkJoinTask<?>)U.getObjectVolatile(a, j);
+                if (t != null) {
+                    if (base == b &&
+                        U.compareAndSwapObject(a, j, t, null)) {
+                        base = b + 1;
+                        return t;
+                    }
+                }
+                else if (base == b) {
+                    if (b + 1 == top)
+                        break;
+                    Thread.yield(); // wait for lagging update
+                }
+            }
+            return null;
+        }
+
+        /**
+         * Takes next task, if one exists, in order specified by mode.
+         */
+        final ForkJoinTask<?> nextLocalTask() {
+            return mode == 0 ? pop() : poll();
+        }
+
+        /**
+         * Returns next task, if one exists, in order specified by mode.
+         */
+        final ForkJoinTask<?> peek() {
+            ForkJoinTask<?>[] a = array; int m;
+            if (a == null || (m = a.length - 1) < 0)
+                return null;
+            int i = mode == 0 ? top - 1 : base;
+            int j = ((i & m) << ASHIFT) + ABASE;
+            return (ForkJoinTask<?>)U.getObjectVolatile(a, j);
+        }
+
+        /**
+         * Pops the given task only if it is at the current top.
+         */
+        final boolean tryUnpush(ForkJoinTask<?> t) {
+            ForkJoinTask<?>[] a; int s;
+            if ((a = array) != null && (s = top) != base &&
+                U.compareAndSwapObject
+                (a, (((a.length - 1) & --s) << ASHIFT) + ABASE, t, null)) {
+                top = s;
+                return true;
+            }
+            return false;
+        }
+
+        /**
+         * Polls the given task only if it is at the current base.
+         */
+        final boolean pollFor(ForkJoinTask<?> task) {
+            ForkJoinTask<?>[] a; int b;
+            if ((b = base) - top < 0 && (a = array) != null) {
+                int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
+                if (U.getObjectVolatile(a, j) == task && base == b &&
+                    U.compareAndSwapObject(a, j, task, null)) {
+                    base = b + 1;
+                    return true;
+                }
+            }
+            return false;
+        }
+
+        /**
+         * Initializes or doubles the capacity of array. Call either
+         * by owner or with lock held -- it is OK for base, but not
+         * top, to move while resizings are in progress.
+         *
+         * @param rejectOnFailure if true, throw exception if capacity
+         * exceeded (relayed ultimately to user); else return null.
+         */
+        final ForkJoinTask<?>[] growArray(boolean rejectOnFailure) {
+            ForkJoinTask<?>[] oldA = array;
+            int size = oldA != null ? oldA.length << 1 : INITIAL_QUEUE_CAPACITY;
+            if (size <= MAXIMUM_QUEUE_CAPACITY) {
+                int oldMask, t, b;
+                ForkJoinTask<?>[] a = array = new ForkJoinTask<?>[size];
+                if (oldA != null && (oldMask = oldA.length - 1) >= 0 &&
+                    (t = top) - (b = base) > 0) {
+                    int mask = size - 1;
+                    do {
+                        ForkJoinTask<?> x;
+                        int oldj = ((b & oldMask) << ASHIFT) + ABASE;
+                        int j    = ((b &    mask) << ASHIFT) + ABASE;
+                        x = (ForkJoinTask<?>)U.getObjectVolatile(oldA, oldj);
+                        if (x != null &&
+                            U.compareAndSwapObject(oldA, oldj, x, null))
+                            U.putObjectVolatile(a, j, x);
+                    } while (++b != t);
+                }
+                return a;
+            }
+            else if (!rejectOnFailure)
+                return null;
+            else
+                throw new RejectedExecutionException("Queue capacity exceeded");
+        }
+
+        /**
+         * Removes and cancels all known tasks, ignoring any exceptions.
+         */
+        final void cancelAll() {
+            ForkJoinTask.cancelIgnoringExceptions(currentJoin);
+            ForkJoinTask.cancelIgnoringExceptions(currentSteal);
+            for (ForkJoinTask<?> t; (t = poll()) != null; )
+                ForkJoinTask.cancelIgnoringExceptions(t);
+        }
+
+        /**
+         * Computes next value for random probes.  Scans don't require
+         * a very high quality generator, but also not a crummy one.
+         * Marsaglia xor-shift is cheap and works well enough.  Note:
+         * This is manually inlined in its usages in ForkJoinPool to
+         * avoid writes inside busy scan loops.
+         */
+        final int nextSeed() {
+            int r = seed;
+            r ^= r << 13;
+            r ^= r >>> 17;
+            return seed = r ^= r << 5;
+        }
+
+        // Execution methods
+
+        /**
+         * Pops and runs tasks until empty.
+         */
+        private void popAndExecAll() {
+            // A bit faster than repeated pop calls
+            ForkJoinTask<?>[] a; int m, s; long j; ForkJoinTask<?> t;
+            while ((a = array) != null && (m = a.length - 1) >= 0 &&
+                   (s = top - 1) - base >= 0 &&
+                   (t = ((ForkJoinTask<?>)
+                         U.getObject(a, j = ((m & s) << ASHIFT) + ABASE)))
+                   != null) {
+                if (U.compareAndSwapObject(a, j, t, null)) {
+                    top = s;
+                    t.doExec();
+                }
+            }
+        }
+
+        /**
+         * Polls and runs tasks until empty.
+         */
+        private void pollAndExecAll() {
+            for (ForkJoinTask<?> t; (t = poll()) != null;)
+                t.doExec();
+        }
+
+        /**
+         * If present, removes from queue and executes the given task, or
+         * any other cancelled task. Returns (true) immediately on any CAS
+         * or consistency check failure so caller can retry.
+         *
+         * @return 0 if no progress can be made, else positive
+         * (this unusual convention simplifies use with tryHelpStealer.)
+         */
+        final int tryRemoveAndExec(ForkJoinTask<?> task) {
+            int stat = 1;
+            boolean removed = false, empty = true;
+            ForkJoinTask<?>[] a; int m, s, b, n;
+            if ((a = array) != null && (m = a.length - 1) >= 0 &&
+                (n = (s = top) - (b = base)) > 0) {
+                for (ForkJoinTask<?> t;;) {           // traverse from s to b
+                    int j = ((--s & m) << ASHIFT) + ABASE;
+                    t = (ForkJoinTask<?>)U.getObjectVolatile(a, j);
+                    if (t == null)                    // inconsistent length
+                        break;
+                    else if (t == task) {
+                        if (s + 1 == top) {           // pop
+                            if (!U.compareAndSwapObject(a, j, task, null))
+                                break;
+                            top = s;
+                            removed = true;
+                        }
+                        else if (base == b)           // replace with proxy
+                            removed = U.compareAndSwapObject(a, j, task,
+                                                             new EmptyTask());
+                        break;
+                    }
+                    else if (t.status >= 0)
+                        empty = false;
+                    else if (s + 1 == top) {          // pop and throw away
+                        if (U.compareAndSwapObject(a, j, t, null))
+                            top = s;
+                        break;
+                    }
+                    if (--n == 0) {
+                        if (!empty && base == b)
+                            stat = 0;
+                        break;
+                    }
+                }
+            }
+            if (removed)
+                task.doExec();
+            return stat;
+        }
+
+        /**
+         * Executes a top-level task and any local tasks remaining
+         * after execution.
+         */
+        final void runTask(ForkJoinTask<?> t) {
+            if (t != null) {
+                currentSteal = t;
+                t.doExec();
+                if (top != base) {       // process remaining local tasks
+                    if (mode == 0)
+                        popAndExecAll();
+                    else
+                        pollAndExecAll();
+                }
+                ++nsteals;
+                currentSteal = null;
+            }
+        }
+
+        /**
+         * Executes a non-top-level (stolen) task.
+         */
+        final void runSubtask(ForkJoinTask<?> t) {
+            if (t != null) {
+                ForkJoinTask<?> ps = currentSteal;
+                currentSteal = t;
+                t.doExec();
+                currentSteal = ps;
+            }
+        }
+
+        /**
+         * Returns true if owned and not known to be blocked.
+         */
+        final boolean isApparentlyUnblocked() {
+            Thread wt; Thread.State s;
+            return (eventCount >= 0 &&
+                    (wt = owner) != null &&
+                    (s = wt.getState()) != Thread.State.BLOCKED &&
+                    s != Thread.State.WAITING &&
+                    s != Thread.State.TIMED_WAITING);
+        }
+
+        /**
+         * If this owned and is not already interrupted, try to
+         * interrupt and/or unpark, ignoring exceptions.
+         */
+        final void interruptOwner() {
+            Thread wt, p;
+            if ((wt = owner) != null && !wt.isInterrupted()) {
+                try {
+                    wt.interrupt();
+                } catch (SecurityException ignore) {
+                }
+            }
+            if ((p = parker) != null)
+                U.unpark(p);
+        }
+
+        // Unsafe mechanics
+        private static final sun.misc.Unsafe U;
+        private static final long RUNSTATE;
+        private static final int ABASE;
+        private static final int ASHIFT;
+        static {
+            int s;
+            try {
+                U = sun.misc.Unsafe.getUnsafe();
+                Class<?> k = WorkQueue.class;
+                Class<?> ak = ForkJoinTask[].class;
+                RUNSTATE = U.objectFieldOffset
+                    (k.getDeclaredField("runState"));
+                ABASE = U.arrayBaseOffset(ak);
+                s = U.arrayIndexScale(ak);
+            } catch (Exception e) {
+                throw new Error(e);
+            }
+            if ((s & (s-1)) != 0)
+                throw new Error("data type scale not a power of two");
+            ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
+        }
+    }
+
+    /**
+     * Per-thread records for threads that submit to pools. Currently
+     * holds only pseudo-random seed / index that is used to choose
+     * submission queues in method doSubmit. In the future, this may
+     * also incorporate a means to implement different task rejection
+     * and resubmission policies.
+     *
+     * Seeds for submitters and workers/workQueues work in basically
+     * the same way but are initialized and updated using slightly
+     * different mechanics. Both are initialized using the same
+     * approach as in class ThreadLocal, where successive values are
+     * unlikely to collide with previous values. This is done during
+     * registration for workers, but requires a separate AtomicInteger
+     * for submitters. Seeds are then randomly modified upon
+     * collisions using xorshifts, which requires a non-zero seed.
+     */
+    static final class Submitter {
+        int seed;
+        Submitter() {
+            int s = nextSubmitterSeed.getAndAdd(SEED_INCREMENT);
+            seed = (s == 0) ? 1 : s; // ensure non-zero
+        }
+    }
+
+    /** ThreadLocal class for Submitters */
+    static final class ThreadSubmitter extends ThreadLocal<Submitter> {
+        public Submitter initialValue() { return new Submitter(); }
+    }
+
+    // static fields (initialized in static initializer below)
+
+    /**
      * Creates a new ForkJoinWorkerThread. This factory is used unless
      * overridden in ForkJoinPool constructors.
      */
@@ -399,107 +1117,86 @@
         defaultForkJoinWorkerThreadFactory;
 
     /**
+     * Generator for assigning sequence numbers as pool names.
+     */
+    private static final AtomicInteger poolNumberGenerator;
+
+    /**
+     * Generator for initial hashes/seeds for submitters. Accessed by
+     * Submitter class constructor.
+     */
+    static final AtomicInteger nextSubmitterSeed;
+
+    /**
      * Permission required for callers of methods that may start or
      * kill threads.
      */
     private static final RuntimePermission modifyThreadPermission;
 
     /**
-     * If there is a security manager, makes sure caller has
-     * permission to modify threads.
+     * Per-thread submission bookeeping. Shared across all pools
+     * to reduce ThreadLocal pollution and because random motion
+     * to avoid contention in one pool is likely to hold for others.
      */
-    private static void checkPermission() {
-        SecurityManager security = System.getSecurityManager();
-        if (security != null)
-            security.checkPermission(modifyThreadPermission);
-    }
+    private static final ThreadSubmitter submitters;
 
-    /**
-     * Generator for assigning sequence numbers as pool names.
-     */
-    private static final AtomicInteger poolNumberGenerator;
+    // static constants
 
     /**
-     * Generator for initial random seeds for worker victim
-     * selection. This is used only to create initial seeds. Random
-     * steals use a cheaper xorshift generator per steal attempt. We
-     * don't expect much contention on seedGenerator, so just use a
-     * plain Random.
+     * The wakeup interval (in nanoseconds) for a worker waiting for a
+     * task when the pool is quiescent to instead try to shrink the
+     * number of workers.  The exact value does not matter too
+     * much. It must be short enough to release resources during
+     * sustained periods of idleness, but not so short that threads
+     * are continually re-created.
      */
-    static final Random workerSeedGenerator;
+    private static final long SHRINK_RATE =
+        4L * 1000L * 1000L * 1000L; // 4 seconds
 
     /**
-     * Array holding all worker threads in the pool.  Initialized upon
-     * construction. Array size must be a power of two.  Updates and
-     * replacements are protected by scanGuard, but the array is
-     * always kept in a consistent enough state to be randomly
-     * accessed without locking by workers performing work-stealing,
-     * as well as other traversal-based methods in this class, so long
-     * as reads memory-acquire by first reading ctl. All readers must
-     * tolerate that some array slots may be null.
+     * The timeout value for attempted shrinkage, includes
+     * some slop to cope with system timer imprecision.
      */
-    ForkJoinWorkerThread[] workers;
-
-    /**
-     * Initial size for submission queue array. Must be a power of
-     * two.  In many applications, these always stay small so we use a
-     * small initial cap.
-     */
-    private static final int INITIAL_QUEUE_CAPACITY = 8;
+    private static final long SHRINK_TIMEOUT = SHRINK_RATE - (SHRINK_RATE / 10);
 
     /**
-     * Maximum size for submission queue array. Must be a power of two
-     * less than or equal to 1 << (31 - width of array entry) to
-     * ensure lack of index wraparound, but is capped at a lower
-     * value to help users trap runaway computations.
-     */
-    private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 24; // 16M
-
-    /**
-     * Array serving as submission queue. Initialized upon construction.
+     * The maximum stolen->joining link depth allowed in method
+     * tryHelpStealer.  Must be a power of two. This value also
+     * controls the maximum number of times to try to help join a task
+     * without any apparent progress or change in pool state before
+     * giving up and blocking (see awaitJoin).  Depths for legitimate
+     * chains are unbounded, but we use a fixed constant to avoid
+     * (otherwise unchecked) cycles and to bound staleness of
+     * traversal parameters at the expense of sometimes blocking when
+     * we could be helping.
      */
-    private ForkJoinTask<?>[] submissionQueue;
-
-    /**
-     * Lock protecting submissions array for addSubmission
-     */
-    private final ReentrantLock submissionLock;
-
-    /**
-     * Condition for awaitTermination, using submissionLock for
-     * convenience.
-     */
-    private final Condition termination;
+    private static final int MAX_HELP = 64;
 
     /**
-     * Creation factory for worker threads.
+     * Secondary time-based bound (in nanosecs) for helping attempts
+     * before trying compensated blocking in awaitJoin. Used in
+     * conjunction with MAX_HELP to reduce variance due to different
+     * polling rates associated with different helping options. The
+     * value should roughly approximate the time required to create
+     * and/or activate a worker thread.
      */
-    private final ForkJoinWorkerThreadFactory factory;
-
-    /**
-     * The uncaught exception handler used when any worker abruptly
-     * terminates.
-     */
-    final Thread.UncaughtExceptionHandler ueh;
+    private static final long COMPENSATION_DELAY = 1L << 18; // ~0.25 millisec
 
     /**
-     * Prefix for assigning names to worker threads
+     * Increment for seed generators. See class ThreadLocal for
+     * explanation.
      */
-    private final String workerNamePrefix;
+    private static final int SEED_INCREMENT = 0x61c88647;
 
     /**
-     * Sum of per-thread steal counts, updated only when threads are
-     * idle or terminating.
-     */
-    private volatile long stealCount;
-
-    /**
-     * Main pool control -- a long packed with:
+     * Bits and masks for control variables
+     *
+     * Field ctl is a long packed with:
      * AC: Number of active running workers minus target parallelism (16 bits)
-     * TC: Number of total workers minus target parallelism (16bits)
+     * TC: Number of total workers minus target parallelism (16 bits)
      * ST: true if pool is terminating (1 bit)
      * EC: the wait count of top waiting thread (15 bits)
-     * ID: ~poolIndex of top of Treiber stack of waiting threads (16 bits)
+     * ID: poolIndex of top of Treiber stack of waiters (16 bits)
      *
      * When convenient, we can extract the upper 32 bits of counts and
      * the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e =
@@ -508,13 +1205,26 @@
      * parallelism and the positionings of fields makes it possible to
      * perform the most common checks via sign tests of fields: When
      * ac is negative, there are not enough active workers, when tc is
-     * negative, there are not enough total workers, when id is
-     * negative, there is at least one waiting worker, and when e is
+     * negative, there are not enough total workers, and when e is
      * negative, the pool is terminating.  To deal with these possibly
      * negative fields, we use casts in and out of "short" and/or
      * signed shifts to maintain signedness.
+     *
+     * When a thread is queued (inactivated), its eventCount field is
+     * set negative, which is the only way to tell if a worker is
+     * prevented from executing tasks, even though it must continue to
+     * scan for them to avoid queuing races. Note however that
+     * eventCount updates lag releases so usage requires care.
+     *
+     * Field runState is an int packed with:
+     * SHUTDOWN: true if shutdown is enabled (1 bit)
+     * SEQ:  a sequence number updated upon (de)registering workers (30 bits)
+     * INIT: set true after workQueues array construction (1 bit)
+     *
+     * The sequence number enables simple consistency checks:
+     * Staleness of read-only operations on the workQueues array can
+     * be checked by comparing runState before vs after the reads.
      */
-    volatile long ctl;
 
     // bit positions/shifts for fields
     private static final int  AC_SHIFT   = 48;
@@ -523,8 +1233,9 @@
     private static final int  EC_SHIFT   = 16;
 
     // bounds
-    private static final int  MAX_ID     = 0x7fff;  // max poolIndex
-    private static final int  SMASK      = 0xffff;  // mask short bits
+    private static final int  SMASK      = 0xffff;  // short bits
+    private static final int  MAX_CAP    = 0x7fff;  // max #workers - 1
+    private static final int  SQMASK     = 0xfffe;  // even short bits
     private static final int  SHORT_SIGN = 1 << 15;
     private static final int  INT_SIGN   = 1 << 31;
 
@@ -546,843 +1257,757 @@
     private static final int  UTC_UNIT   = 1 << UTC_SHIFT;
 
     // masks and units for dealing with e = (int)ctl
-    private static final int  E_MASK     = 0x7fffffff; // no STOP_BIT
-    private static final int  EC_UNIT    = 1 << EC_SHIFT;
-
-    /**
-     * The target parallelism level.
-     */
-    final int parallelism;
+    private static final int E_MASK      = 0x7fffffff; // no STOP_BIT
+    private static final int E_SEQ       = 1 << EC_SHIFT;
 
-    /**
-     * Index (mod submission queue length) of next element to take
-     * from submission queue. Usage is identical to that for
-     * per-worker queues -- see ForkJoinWorkerThread internal
-     * documentation.
-     */
-    volatile int queueBase;
+    // runState bits
+    private static final int SHUTDOWN    = 1 << 31;
 
-    /**
-     * Index (mod submission queue length) of next element to add
-     * in submission queue. Usage is identical to that for
-     * per-worker queues -- see ForkJoinWorkerThread internal
-     * documentation.
-     */
-    int queueTop;
+    // access mode for WorkQueue
+    static final int LIFO_QUEUE          =  0;
+    static final int FIFO_QUEUE          =  1;
+    static final int SHARED_QUEUE        = -1;
 
-    /**
-     * True when shutdown() has been called.
-     */
-    volatile boolean shutdown;
-
-    /**
-     * True if use local fifo, not default lifo, for local polling
-     * Read by, and replicated by ForkJoinWorkerThreads
-     */
-    final boolean locallyFifo;
+    // Instance fields
 
-    /**
-     * The number of threads in ForkJoinWorkerThreads.helpQuiescePool.
-     * When non-zero, suppresses automatic shutdown when active
-     * counts become zero.
+    /*
+     * Field layout order in this class tends to matter more than one
+     * would like. Runtime layout order is only loosely related to
+     * declaration order and may differ across JVMs, but the following
+     * empirically works OK on current JVMs.
      */
-    volatile int quiescerCount;
-
-    /**
-     * The number of threads blocked in join.
-     */
-    volatile int blockedCount;
-
-    /**
-     * Counter for worker Thread names (unrelated to their poolIndex)
-     */
-    private volatile int nextWorkerNumber;
 
-    /**
-     * The index for the next created worker. Accessed under scanGuard.
-     */
-    private int nextWorkerIndex;
+    volatile long ctl;                         // main pool control
+    final int parallelism;                     // parallelism level
+    final int localMode;                       // per-worker scheduling mode
+    final int submitMask;                      // submit queue index bound
+    int nextSeed;                              // for initializing worker seeds
+    volatile int runState;                     // shutdown status and seq
+    WorkQueue[] workQueues;                    // main registry
+    final Mutex lock;                          // for registration
+    final Condition termination;               // for awaitTermination
+    final ForkJoinWorkerThreadFactory factory; // factory for new workers
+    final Thread.UncaughtExceptionHandler ueh; // per-worker UEH
+    final AtomicLong stealCount;               // collect counts when terminated
+    final AtomicInteger nextWorkerNumber;      // to create worker name string
+    final String workerNamePrefix;             // to create worker name string
 
-    /**
-     * SeqLock and index masking for updates to workers array.  Locked
-     * when SG_UNIT is set. Unlocking clears bit by adding
-     * SG_UNIT. Staleness of read-only operations can be checked by
-     * comparing scanGuard to value before the reads. The low 16 bits
-     * (i.e, anding with SMASK) hold (the smallest power of two
-     * covering all worker indices, minus one, and is used to avoid
-     * dealing with large numbers of null slots when the workers array
-     * is overallocated.
-     */
-    volatile int scanGuard;
-
-    private static final int SG_UNIT = 1 << 16;
+    //  Creating, registering, and deregistering workers
 
     /**
-     * The wakeup interval (in nanoseconds) for a worker waiting for a
-     * task when the pool is quiescent to instead try to shrink the
-     * number of workers.  The exact value does not matter too
-     * much. It must be short enough to release resources during
-     * sustained periods of idleness, but not so short that threads
-     * are continually re-created.
+     * Tries to create and start a worker
      */
-    private static final long SHRINK_RATE =
-        4L * 1000L * 1000L * 1000L; // 4 seconds
+    private void addWorker() {
+        Throwable ex = null;
+        ForkJoinWorkerThread wt = null;
+        try {
+            if ((wt = factory.newThread(this)) != null) {
+                wt.start();
+                return;
+            }
+        } catch (Throwable e) {
+            ex = e;
+        }
+        deregisterWorker(wt, ex); // adjust counts etc on failure
+    }
 
     /**
-     * Top-level loop for worker threads: On each step: if the
-     * previous step swept through all queues and found no tasks, or
-     * there are excess threads, then possibly blocks. Otherwise,
-     * scans for and, if found, executes a task. Returns when pool
-     * and/or worker terminate.
-     *
-     * @param w the worker
+     * Callback from ForkJoinWorkerThread constructor to assign a
+     * public name. This must be separate from registerWorker because
+     * it is called during the "super" constructor call in
+     * ForkJoinWorkerThread.
      */
-    final void work(ForkJoinWorkerThread w) {
-        boolean swept = false;                // true on empty scans
-        long c;
-        while (!w.terminate && (int)(c = ctl) >= 0) {
-            int a;                            // active count
-            if (!swept && (a = (int)(c >> AC_SHIFT)) <= 0)
-                swept = scan(w, a);
-            else if (tryAwaitWork(w, c))
-                swept = false;
-        }
+    final String nextWorkerName() {
+        return workerNamePrefix.concat
+            (Integer.toString(nextWorkerNumber.addAndGet(1)));
     }
 
-    // Signalling
-
     /**
-     * Wakes up or creates a worker.
+     * Callback from ForkJoinWorkerThread constructor to establish its
+     * poolIndex and record its WorkQueue. To avoid scanning bias due
+     * to packing entries in front of the workQueues array, we treat
+     * the array as a simple power-of-two hash table using per-thread
+     * seed as hash, expanding as needed.
+     *
+     * @param w the worker's queue
      */
-    final void signalWork() {
-        /*
-         * The while condition is true if: (there is are too few total
-         * workers OR there is at least one waiter) AND (there are too
-         * few active workers OR the pool is terminating).  The value
-         * of e distinguishes the remaining cases: zero (no waiters)
-         * for create, negative if terminating (in which case do
-         * nothing), else release a waiter. The secondary checks for
-         * release (non-null array etc) can fail if the pool begins
-         * terminating after the test, and don't impose any added cost
-         * because JVMs must perform null and bounds checks anyway.
-         */
-        long c; int e, u;
-        while ((((e = (int)(c = ctl)) | (u = (int)(c >>> 32))) &
-                (INT_SIGN|SHORT_SIGN)) == (INT_SIGN|SHORT_SIGN) && e >= 0) {
-            if (e > 0) {                         // release a waiting worker
-                int i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
-                if ((ws = workers) == null ||
-                    (i = ~e & SMASK) >= ws.length ||
-                    (w = ws[i]) == null)
-                    break;
-                long nc = (((long)(w.nextWait & E_MASK)) |
-                           ((long)(u + UAC_UNIT) << 32));
-                if (w.eventCount == e &&
-                    UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
-                    w.eventCount = (e + EC_UNIT) & E_MASK;
-                    if (w.parked)
-                        UNSAFE.unpark(w);
-                    break;
+
+    final void registerWorker(WorkQueue w) {
+        Mutex lock = this.lock;
+        lock.lock();
+        try {
+            WorkQueue[] ws = workQueues;
+            if (w != null && ws != null) {          // skip on shutdown/failure
+                int rs, n =  ws.length, m = n - 1;
+                int s = nextSeed += SEED_INCREMENT; // rarely-colliding sequence
+                w.seed = (s == 0) ? 1 : s;          // ensure non-zero seed
+                int r = (s << 1) | 1;               // use odd-numbered indices
+                if (ws[r &= m] != null) {           // collision
+                    int probes = 0;                 // step by approx half size
+                    int step = (n <= 4) ? 2 : ((n >>> 1) & SQMASK) + 2;
+                    while (ws[r = (r + step) & m] != null) {
+                        if (++probes >= n) {
+                            workQueues = ws = Arrays.copyOf(ws, n <<= 1);
+                            m = n - 1;
+                            probes = 0;
+                        }
+                    }
                 }
+                w.eventCount = w.poolIndex = r;     // establish before recording
+                ws[r] = w;                          // also update seq
+                runState = ((rs = runState) & SHUTDOWN) | ((rs + 2) & ~SHUTDOWN);
             }
-            else if (UNSAFE.compareAndSwapLong
-                     (this, ctlOffset, c,
-                      (long)(((u + UTC_UNIT) & UTC_MASK) |
-                             ((u + UAC_UNIT) & UAC_MASK)) << 32)) {
-                addWorker();
-                break;
-            }
+        } finally {
+            lock.unlock();
         }
     }
 
     /**
-     * Variant of signalWork to help release waiters on rescans.
-     * Tries once to release a waiter if active count < 0.
+     * Final callback from terminating worker, as well as upon failure
+     * to construct or start a worker in addWorker.  Removes record of
+     * worker from array, and adjusts counts. If pool is shutting
+     * down, tries to complete termination.
      *
-     * @return false if failed due to contention, else true
+     * @param wt the worker thread or null if addWorker failed
+     * @param ex the exception causing failure, or null if none
+     */
+    final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) {
+        Mutex lock = this.lock;
+        WorkQueue w = null;
+        if (wt != null && (w = wt.workQueue) != null) {
+            w.runState = -1;                // ensure runState is set
+            stealCount.getAndAdd(w.totalSteals + w.nsteals);
+            int idx = w.poolIndex;
+            lock.lock();
+            try {                           // remove record from array
+                WorkQueue[] ws = workQueues;
+                if (ws != null && idx >= 0 && idx < ws.length && ws[idx] == w)
+                    ws[idx] = null;
+            } finally {
+                lock.unlock();
+            }
+        }
+
+        long c;                             // adjust ctl counts
+        do {} while (!U.compareAndSwapLong
+                     (this, CTL, c = ctl, (((c - AC_UNIT) & AC_MASK) |
+                                           ((c - TC_UNIT) & TC_MASK) |
+                                           (c & ~(AC_MASK|TC_MASK)))));
+
+        if (!tryTerminate(false, false) && w != null) {
+            w.cancelAll();                  // cancel remaining tasks
+            if (w.array != null)            // suppress signal if never ran
+                signalWork();               // wake up or create replacement
+            if (ex == null)                 // help clean refs on way out
+                ForkJoinTask.helpExpungeStaleExceptions();
+        }
+
+        if (ex != null)                     // rethrow
+            U.throwException(ex);
+    }
+
+
+    // Submissions
+
+    /**
+     * Unless shutting down, adds the given task to a submission queue
+     * at submitter's current queue index (modulo submission
+     * range). If no queue exists at the index, one is created.  If
+     * the queue is busy, another index is randomly chosen. The
+     * submitMask bounds the effective number of queues to the
+     * (nearest power of two for) parallelism level.
+     *
+     * @param task the task. Caller must ensure non-null.
      */
-    private boolean tryReleaseWaiter() {
-        long c; int e, i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
-        if ((e = (int)(c = ctl)) > 0 &&
-            (int)(c >> AC_SHIFT) < 0 &&
-            (ws = workers) != null &&
-            (i = ~e & SMASK) < ws.length &&
-            (w = ws[i]) != null) {
-            long nc = ((long)(w.nextWait & E_MASK) |
-                       ((c + AC_UNIT) & (AC_MASK|TC_MASK)));
-            if (w.eventCount != e ||
-                !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
-                return false;
-            w.eventCount = (e + EC_UNIT) & E_MASK;
-            if (w.parked)
-                UNSAFE.unpark(w);
+    private void doSubmit(ForkJoinTask<?> task) {
+        Submitter s = submitters.get();
+        for (int r = s.seed, m = submitMask;;) {
+            WorkQueue[] ws; WorkQueue q;
+            int k = r & m & SQMASK;          // use only even indices
+            if (runState < 0 || (ws = workQueues) == null || ws.length <= k)
+                throw new RejectedExecutionException(); // shutting down
+            else if ((q = ws[k]) == null) {  // create new queue
+                WorkQueue nq = new WorkQueue(this, null, SHARED_QUEUE);
+                Mutex lock = this.lock;      // construct outside lock
+                lock.lock();
+                try {                        // recheck under lock
+                    int rs = runState;       // to update seq
+                    if (ws == workQueues && ws[k] == null) {
+                        ws[k] = nq;
+                        runState = ((rs & SHUTDOWN) | ((rs + 2) & ~SHUTDOWN));
+                    }
+                } finally {
+                    lock.unlock();
+                }
+            }
+            else if (q.trySharedPush(task)) {
+                signalWork();
+                return;
+            }
+            else if (m > 1) {                // move to a different index
+                r ^= r << 13;                // same xorshift as WorkQueues
+                r ^= r >>> 17;
+                s.seed = r ^= r << 5;
+            }
+            else
+                Thread.yield();              // yield if no alternatives
         }
-        return true;
+    }
+
+    // Maintaining ctl counts
+
+    /**
+     * Increments active count; mainly called upon return from blocking.
+     */
+    final void incrementActiveCount() {
+        long c;
+        do {} while (!U.compareAndSwapLong(this, CTL, c = ctl, c + AC_UNIT));
+    }
+
+    /**
+     * Tries to activate or create a worker if too few are active.
+     */
+    final void signalWork() {
+        long c; int u;
+        while ((u = (int)((c = ctl) >>> 32)) < 0) {     // too few active
+            WorkQueue[] ws = workQueues; int e, i; WorkQueue w; Thread p;
+            if ((e = (int)c) > 0) {                     // at least one waiting
+                if (ws != null && (i = e & SMASK) < ws.length &&
+                    (w = ws[i]) != null && w.eventCount == (e | INT_SIGN)) {
+                    long nc = (((long)(w.nextWait & E_MASK)) |
+                               ((long)(u + UAC_UNIT) << 32));
+                    if (U.compareAndSwapLong(this, CTL, c, nc)) {
+                        w.eventCount = (e + E_SEQ) & E_MASK;
+                        if ((p = w.parker) != null)
+                            U.unpark(p);                // activate and release
+                        break;
+                    }
+                }
+                else
+                    break;
+            }
+            else if (e == 0 && (u & SHORT_SIGN) != 0) { // too few total
+                long nc = (long)(((u + UTC_UNIT) & UTC_MASK) |
+                                 ((u + UAC_UNIT) & UAC_MASK)) << 32;
+                if (U.compareAndSwapLong(this, CTL, c, nc)) {
+                    addWorker();
+                    break;
+                }
+            }
+            else
+                break;
+        }
     }
 
     // Scanning for tasks
 
     /**
-     * Scans for and, if found, executes one task. Scans start at a
-     * random index of workers array, and randomly select the first
-     * (2*#workers)-1 probes, and then, if all empty, resort to 2
-     * circular sweeps, which is necessary to check quiescence. and
-     * taking a submission only if no stealable tasks were found.  The
-     * steal code inside the loop is a specialized form of
-     * ForkJoinWorkerThread.deqTask, followed bookkeeping to support
-     * helpJoinTask and signal propagation. The code for submission
-     * queues is almost identical. On each steal, the worker completes
-     * not only the task, but also all local tasks that this task may
-     * have generated. On detecting staleness or contention when
-     * trying to take a task, this method returns without finishing
-     * sweep, which allows global state rechecks before retry.
-     *
-     * @param w the worker
-     * @param a the number of active workers
-     * @return true if swept all queues without finding a task
+     * Top-level runloop for workers, called by ForkJoinWorkerThread.run.
      */
-    private boolean scan(ForkJoinWorkerThread w, int a) {
-        int g = scanGuard; // mask 0 avoids useless scans if only one active
-        int m = (parallelism == 1 - a && blockedCount == 0) ? 0 : g & SMASK;
-        ForkJoinWorkerThread[] ws = workers;
-        if (ws == null || ws.length <= m)         // staleness check
-            return false;
-        for (int r = w.seed, k = r, j = -(m + m); j <= m + m; ++j) {
-            ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
-            ForkJoinWorkerThread v = ws[k & m];
-            if (v != null && (b = v.queueBase) != v.queueTop &&
-                (q = v.queue) != null && (i = (q.length - 1) & b) >= 0) {
-                long u = (i << ASHIFT) + ABASE;
-                if ((t = q[i]) != null && v.queueBase == b &&
-                    UNSAFE.compareAndSwapObject(q, u, t, null)) {
-                    int d = (v.queueBase = b + 1) - v.queueTop;
-                    v.stealHint = w.poolIndex;
-                    if (d != 0)
-                        signalWork();             // propagate if nonempty
-                    w.execTask(t);
-                }
-                r ^= r << 13; r ^= r >>> 17; w.seed = r ^ (r << 5);
-                return false;                     // store next seed
-            }
-            else if (j < 0) {                     // xorshift
-                r ^= r << 13; r ^= r >>> 17; k = r ^= r << 5;
-            }
-            else
-                ++k;
-        }
-        if (scanGuard != g)                       // staleness check
-            return false;
-        else {                                    // try to take submission
-            ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
-            if ((b = queueBase) != queueTop &&
-                (q = submissionQueue) != null &&
-                (i = (q.length - 1) & b) >= 0) {
-                long u = (i << ASHIFT) + ABASE;
-                if ((t = q[i]) != null && queueBase == b &&
-                    UNSAFE.compareAndSwapObject(q, u, t, null)) {
-                    queueBase = b + 1;
-                    w.execTask(t);
-                }
-                return false;
-            }
-            return true;                         // all queues empty
-        }
+    final void runWorker(WorkQueue w) {
+        w.growArray(false);         // initialize queue array in this thread
+        do { w.runTask(scan(w)); } while (w.runState >= 0);
     }
 
     /**
-     * Tries to enqueue worker w in wait queue and await change in
-     * worker's eventCount.  If the pool is quiescent and there is
-     * more than one worker, possibly terminates worker upon exit.
-     * Otherwise, before blocking, rescans queues to avoid missed
-     * signals.  Upon finding work, releases at least one worker
-     * (which may be the current worker). Rescans restart upon
-     * detected staleness or failure to release due to
-     * contention. Note the unusual conventions about Thread.interrupt
-     * here and elsewhere: Because interrupts are used solely to alert
-     * threads to check termination, which is checked here anyway, we
-     * clear status (using Thread.interrupted) before any call to
-     * park, so that park does not immediately return due to status
-     * being set via some other unrelated call to interrupt in user
-     * code.
+     * Scans for and, if found, returns one task, else possibly
+     * inactivates the worker. This method operates on single reads of
+     * volatile state and is designed to be re-invoked continuously,
+     * in part because it returns upon detecting inconsistencies,
+     * contention, or state changes that indicate possible success on
+     * re-invocation.
+     *
+     * The scan searches for tasks across a random permutation of
+     * queues (starting at a random index and stepping by a random
+     * relative prime, checking each at least once).  The scan
+     * terminates upon either finding a non-empty queue, or completing
+     * the sweep. If the worker is not inactivated, it takes and
+     * returns a task from this queue.  On failure to find a task, we
+     * take one of the following actions, after which the caller will
+     * retry calling this method unless terminated.
+     *
+     * * If pool is terminating, terminate the worker.
      *
-     * @param w the calling worker
-     * @param c the ctl value on entry
-     * @return true if waited or another thread was released upon enq
+     * * If not a complete sweep, try to release a waiting worker.  If
+     * the scan terminated because the worker is inactivated, then the
+     * released worker will often be the calling worker, and it can
+     * succeed obtaining a task on the next call. Or maybe it is
+     * another worker, but with same net effect. Releasing in other
+     * cases as well ensures that we have enough workers running.
+     *
+     * * If not already enqueued, try to inactivate and enqueue the
+     * worker on wait queue. Or, if inactivating has caused the pool
+     * to be quiescent, relay to idleAwaitWork to check for
+     * termination and possibly shrink pool.
+     *
+     * * If already inactive, and the caller has run a task since the
+     * last empty scan, return (to allow rescan) unless others are
+     * also inactivated.  Field WorkQueue.rescans counts down on each
+     * scan to ensure eventual inactivation and blocking.
+     *
+     * * If already enqueued and none of the above apply, park
+     * awaiting signal,
+     *
+     * @param w the worker (via its WorkQueue)
+     * @return a task or null of none found
      */
-    private boolean tryAwaitWork(ForkJoinWorkerThread w, long c) {
-        int v = w.eventCount;
-        w.nextWait = (int)c;                      // w's successor record
-        long nc = (long)(v & E_MASK) | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
-        if (ctl != c || !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
-            long d = ctl; // return true if lost to a deq, to force scan
-            return (int)d != (int)c && ((d - c) & AC_MASK) >= 0L;
-        }
-        for (int sc = w.stealCount; sc != 0;) {   // accumulate stealCount
-            long s = stealCount;
-            if (UNSAFE.compareAndSwapLong(this, stealCountOffset, s, s + sc))
-                sc = w.stealCount = 0;
-            else if (w.eventCount != v)
-                return true;                      // update next time
-        }
-        if ((!shutdown || !tryTerminate(false)) &&
-            (int)c != 0 && parallelism + (int)(nc >> AC_SHIFT) == 0 &&
-            blockedCount == 0 && quiescerCount == 0)
-            idleAwaitWork(w, nc, c, v);           // quiescent
-        for (boolean rescanned = false;;) {
-            if (w.eventCount != v)
-                return true;
-            if (!rescanned) {
-                int g = scanGuard, m = g & SMASK;
-                ForkJoinWorkerThread[] ws = workers;
-                if (ws != null && m < ws.length) {
-                    rescanned = true;
-                    for (int i = 0; i <= m; ++i) {
-                        ForkJoinWorkerThread u = ws[i];
-                        if (u != null) {
-                            if (u.queueBase != u.queueTop &&
-                                !tryReleaseWaiter())
-                                rescanned = false; // contended
-                            if (w.eventCount != v)
-                                return true;
-                        }
+    private final ForkJoinTask<?> scan(WorkQueue w) {
+        WorkQueue[] ws;                       // first update random seed
+        int r = w.seed; r ^= r << 13; r ^= r >>> 17; w.seed = r ^= r << 5;
+        int rs = runState, m;                 // volatile read order matters
+        if ((ws = workQueues) != null && (m = ws.length - 1) > 0) {
+            int ec = w.eventCount;            // ec is negative if inactive
+            int step = (r >>> 16) | 1;        // relative prime
+            for (int j = (m + 1) << 2; ; r += step) {
+                WorkQueue q; ForkJoinTask<?> t; ForkJoinTask<?>[] a; int b;
+                if ((q = ws[r & m]) != null && (b = q.base) - q.top < 0 &&
+                    (a = q.array) != null) {  // probably nonempty
+                    int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
+                    t = (ForkJoinTask<?>)U.getObjectVolatile(a, i);
+                    if (q.base == b && ec >= 0 && t != null &&
+                        U.compareAndSwapObject(a, i, t, null)) {
+                        if (q.top - (q.base = b + 1) > 1)
+                            signalWork();    // help pushes signal
+                        return t;
+                    }
+                    else if (ec < 0 || j <= m) {
+                        rs = 0;               // mark scan as imcomplete
+                        break;                // caller can retry after release
                     }
                 }
-                if (scanGuard != g ||              // stale
-                    (queueBase != queueTop && !tryReleaseWaiter()))
-                    rescanned = false;
-                if (!rescanned)
-                    Thread.yield();                // reduce contention
-                else
-                    Thread.interrupted();          // clear before park
+                if (--j < 0)
+                    break;
+            }
+
+            long c = ctl; int e = (int)c, a = (int)(c >> AC_SHIFT), nr, ns;
+            if (e < 0)                        // decode ctl on empty scan
+                w.runState = -1;              // pool is terminating
+            else if (rs == 0 || rs != runState) { // incomplete scan
+                WorkQueue v; Thread p;        // try to release a waiter
+                if (e > 0 && a < 0 && w.eventCount == ec &&
+                    (v = ws[e & m]) != null && v.eventCount == (e | INT_SIGN)) {
+                    long nc = ((long)(v.nextWait & E_MASK) |
+                               ((c + AC_UNIT) & (AC_MASK|TC_MASK)));
+                    if (ctl == c && U.compareAndSwapLong(this, CTL, c, nc)) {
+                        v.eventCount = (e + E_SEQ) & E_MASK;
+                        if ((p = v.parker) != null)
+                            U.unpark(p);
+                    }
+                }
             }
-            else {
-                w.parked = true;                   // must recheck
-                if (w.eventCount != v) {
-                    w.parked = false;
-                    return true;
+            else if (ec >= 0) {               // try to enqueue/inactivate
+                long nc = (long)ec | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
+                w.nextWait = e;
+                w.eventCount = ec | INT_SIGN; // mark as inactive
+                if (ctl != c || !U.compareAndSwapLong(this, CTL, c, nc))
+                    w.eventCount = ec;        // unmark on CAS failure
+                else {
+                    if ((ns = w.nsteals) != 0) {
+                        w.nsteals = 0;        // set rescans if ran task
+                        w.rescans = (a > 0) ? 0 : a + parallelism;
+                        w.totalSteals += ns;
+                    }
+                    if (a == 1 - parallelism) // quiescent
+                        idleAwaitWork(w, nc, c);
                 }
-                LockSupport.park(this);
-                rescanned = w.parked = false;
+            }
+            else if (w.eventCount < 0) {      // already queued
+                if ((nr = w.rescans) > 0) {   // continue rescanning
+                    int ac = a + parallelism;
+                    if (((w.rescans = (ac < nr) ? ac : nr - 1) & 3) == 0)
+                        Thread.yield();       // yield before block
+                }
+                else {
+                    Thread.interrupted();     // clear status
+                    Thread wt = Thread.currentThread();
+                    U.putObject(wt, PARKBLOCKER, this);
+                    w.parker = wt;            // emulate LockSupport.park
+                    if (w.eventCount < 0)     // recheck
+                        U.park(false, 0L);
+                    w.parker = null;
+                    U.putObject(wt, PARKBLOCKER, null);
+                }
             }
         }
+        return null;
     }
 
     /**
-     * If inactivating worker w has caused pool to become
-     * quiescent, check for pool termination, and wait for event
-     * for up to SHRINK_RATE nanosecs (rescans are unnecessary in
-     * this case because quiescence reflects consensus about lack
-     * of work). On timeout, if ctl has not changed, terminate the
-     * worker. Upon its termination (see deregisterWorker), it may
-     * wake up another worker to possibly repeat this process.
+     * If inactivating worker w has caused the pool to become
+     * quiescent, checks for pool termination, and, so long as this is
+     * not the only worker, waits for event for up to SHRINK_RATE
+     * nanosecs.  On timeout, if ctl has not changed, terminates the
+     * worker, which will in turn wake up another worker to possibly
+     * repeat this process.
      *
      * @param w the calling worker
-     * @param currentCtl the ctl value after enqueuing w
-     * @param prevCtl the ctl value if w terminated
-     * @param v the eventCount w awaits change
+     * @param currentCtl the ctl value triggering possible quiescence
+     * @param prevCtl the ctl value to restore if thread is terminated
      */
-    private void idleAwaitWork(ForkJoinWorkerThread w, long currentCtl,
-                               long prevCtl, int v) {
-        if (w.eventCount == v) {
-            if (shutdown)
-                tryTerminate(false);
-            ForkJoinTask.helpExpungeStaleExceptions(); // help clean weak refs
+    private void idleAwaitWork(WorkQueue w, long currentCtl, long prevCtl) {
+        if (w.eventCount < 0 && !tryTerminate(false, false) &&
+            (int)prevCtl != 0 && !hasQueuedSubmissions() && ctl == currentCtl) {
+            Thread wt = Thread.currentThread();
+            Thread.yield();            // yield before block
             while (ctl == currentCtl) {
                 long startTime = System.nanoTime();
-                w.parked = true;
-                if (w.eventCount == v)             // must recheck
-                    LockSupport.parkNanos(this, SHRINK_RATE);
-                w.parked = false;
-                if (w.eventCount != v)
+                Thread.interrupted();  // timed variant of version in scan()
+                U.putObject(wt, PARKBLOCKER, this);
+                w.parker = wt;
+                if (ctl == currentCtl)
+                    U.park(false, SHRINK_RATE);
+                w.parker = null;
+                U.putObject(wt, PARKBLOCKER, null);
+                if (ctl != currentCtl)
                     break;
-                else if (System.nanoTime() - startTime <
-                         SHRINK_RATE - (SHRINK_RATE / 10)) // timing slop
-                    Thread.interrupted();          // spurious wakeup
-                else if (UNSAFE.compareAndSwapLong(this, ctlOffset,
-                                                   currentCtl, prevCtl)) {
-                    w.terminate = true;            // restore previous
-                    w.eventCount = ((int)currentCtl + EC_UNIT) & E_MASK;
+                if (System.nanoTime() - startTime >= SHRINK_TIMEOUT &&
+                    U.compareAndSwapLong(this, CTL, currentCtl, prevCtl)) {
+                    w.eventCount = (w.eventCount + E_SEQ) | E_MASK;
+                    w.runState = -1;   // shrink
                     break;
                 }
             }
         }
     }
 
-    // Submissions
-
     /**
-     * Enqueues the given task in the submissionQueue.  Same idea as
-     * ForkJoinWorkerThread.pushTask except for use of submissionLock.
+     * Tries to locate and execute tasks for a stealer of the given
+     * task, or in turn one of its stealers, Traces currentSteal ->
+     * currentJoin links looking for a thread working on a descendant
+     * of the given task and with a non-empty queue to steal back and
+     * execute tasks from. The first call to this method upon a
+     * waiting join will often entail scanning/search, (which is OK
+     * because the joiner has nothing better to do), but this method
+     * leaves hints in workers to speed up subsequent calls. The
+     * implementation is very branchy to cope with potential
+     * inconsistencies or loops encountering chains that are stale,
+     * unknown, or so long that they are likely cyclic.
      *
-     * @param t the task
+     * @param joiner the joining worker
+     * @param task the task to join
+     * @return 0 if no progress can be made, negative if task
+     * known complete, else positive
      */
-    private void addSubmission(ForkJoinTask<?> t) {
-        final ReentrantLock lock = this.submissionLock;
-        lock.lock();
-        try {
-            ForkJoinTask<?>[] q; int s, m;
-            if ((q = submissionQueue) != null) {    // ignore if queue removed
-                long u = (((s = queueTop) & (m = q.length-1)) << ASHIFT)+ABASE;
-                UNSAFE.putOrderedObject(q, u, t);
-                queueTop = s + 1;
-                if (s - queueBase == m)
-                    growSubmissionQueue();
-            }
-        } finally {
-            lock.unlock();
-        }
-        signalWork();
-    }
-
-    //  (pollSubmission is defined below with exported methods)
-
-    /**
-     * Creates or doubles submissionQueue array.
-     * Basically identical to ForkJoinWorkerThread version.
-     */
-    private void growSubmissionQueue() {
-        ForkJoinTask<?>[] oldQ = submissionQueue;
-        int size = oldQ != null ? oldQ.length << 1 : INITIAL_QUEUE_CAPACITY;
-        if (size > MAXIMUM_QUEUE_CAPACITY)
-            throw new RejectedExecutionException("Queue capacity exceeded");
-        if (size < INITIAL_QUEUE_CAPACITY)
-            size = INITIAL_QUEUE_CAPACITY;
-        ForkJoinTask<?>[] q = submissionQueue = new ForkJoinTask<?>[size];
-        int mask = size - 1;
-        int top = queueTop;
-        int oldMask;
-        if (oldQ != null && (oldMask = oldQ.length - 1) >= 0) {
-            for (int b = queueBase; b != top; ++b) {
-                long u = ((b & oldMask) << ASHIFT) + ABASE;
-                Object x = UNSAFE.getObjectVolatile(oldQ, u);
-                if (x != null && UNSAFE.compareAndSwapObject(oldQ, u, x, null))
-                    UNSAFE.putObjectVolatile
-                        (q, ((b & mask) << ASHIFT) + ABASE, x);
+    private int tryHelpStealer(WorkQueue joiner, ForkJoinTask<?> task) {
+        int stat = 0, steps = 0;                    // bound to avoid cycles
+        if (joiner != null && task != null) {       // hoist null checks
+            restart: for (;;) {
+                ForkJoinTask<?> subtask = task;     // current target
+                for (WorkQueue j = joiner, v;;) {   // v is stealer of subtask
+                    WorkQueue[] ws; int m, s, h;
+                    if ((s = task.status) < 0) {
+                        stat = s;
+                        break restart;
+                    }
+                    if ((ws = workQueues) == null || (m = ws.length - 1) <= 0)
+                        break restart;              // shutting down
+                    if ((v = ws[h = (j.stealHint | 1) & m]) == null ||
+                        v.currentSteal != subtask) {
+                        for (int origin = h;;) {    // find stealer
+                            if (((h = (h + 2) & m) & 15) == 1 &&
+                                (subtask.status < 0 || j.currentJoin != subtask))
+                                continue restart;   // occasional staleness check
+                            if ((v = ws[h]) != null &&
+                                v.currentSteal == subtask) {
+                                j.stealHint = h;    // save hint
+                                break;
+                            }
+                            if (h == origin)
+                                break restart;      // cannot find stealer
+                        }
+                    }
+                    for (;;) { // help stealer or descend to its stealer
+                        ForkJoinTask[] a;  int b;
+                        if (subtask.status < 0)     // surround probes with
+                            continue restart;       //   consistency checks
+                        if ((b = v.base) - v.top < 0 && (a = v.array) != null) {
+                            int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
+                            ForkJoinTask<?> t =
+                                (ForkJoinTask<?>)U.getObjectVolatile(a, i);
+                            if (subtask.status < 0 || j.currentJoin != subtask ||
+                                v.currentSteal != subtask)
+                                continue restart;   // stale
+                            stat = 1;               // apparent progress
+                            if (t != null && v.base == b &&
+                                U.compareAndSwapObject(a, i, t, null)) {
+                                v.base = b + 1;     // help stealer
+                                joiner.runSubtask(t);
+                            }
+                            else if (v.base == b && ++steps == MAX_HELP)
+                                break restart;      // v apparently stalled
+                        }
+                        else {                      // empty -- try to descend
+                            ForkJoinTask<?> next = v.currentJoin;
+                            if (subtask.status < 0 || j.currentJoin != subtask ||
+                                v.currentSteal != subtask)
+                                continue restart;   // stale
+                            else if (next == null || ++steps == MAX_HELP)
+                                break restart;      // dead-end or maybe cyclic
+                            else {
+                                subtask = next;
+                                j = v;
+                                break;
+                            }
+                        }
+                    }
+                }
             }
         }
-    }
-
-    // Blocking support
-
-    /**
-     * Tries to increment blockedCount, decrement active count
-     * (sometimes implicitly) and possibly release or create a
-     * compensating worker in preparation for blocking. Fails
-     * on contention or termination.
-     *
-     * @return true if the caller can block, else should recheck and retry
-     */
-    private boolean tryPreBlock() {
-        int b = blockedCount;
-        if (UNSAFE.compareAndSwapInt(this, blockedCountOffset, b, b + 1)) {
-            int pc = parallelism;
-            do {
-                ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
-                int e, ac, tc, rc, i;
-                long c = ctl;
-                int u = (int)(c >>> 32);
-                if ((e = (int)c) < 0) {
-                                                 // skip -- terminating
-                }
-                else if ((ac = (u >> UAC_SHIFT)) <= 0 && e != 0 &&
-                         (ws = workers) != null &&
-                         (i = ~e & SMASK) < ws.length &&
-                         (w = ws[i]) != null) {
-                    long nc = ((long)(w.nextWait & E_MASK) |
-                               (c & (AC_MASK|TC_MASK)));
-                    if (w.eventCount == e &&
-                        UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
-                        w.eventCount = (e + EC_UNIT) & E_MASK;
-                        if (w.parked)
-                            UNSAFE.unpark(w);
-                        return true;             // release an idle worker
-                    }
-                }
-                else if ((tc = (short)(u >>> UTC_SHIFT)) >= 0 && ac + pc > 1) {
-                    long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
-                    if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
-                        return true;             // no compensation needed
-                }
-                else if (tc + pc < MAX_ID) {
-                    long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
-                    if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
-                        addWorker();
-                        return true;            // create a replacement
-                    }
-                }
-                // try to back out on any failure and let caller retry
-            } while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
-                                               b = blockedCount, b - 1));
-        }
-        return false;
-    }
-
-    /**
-     * Decrements blockedCount and increments active count
-     */
-    private void postBlock() {
-        long c;
-        do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset,  // no mask
-                                                c = ctl, c + AC_UNIT));
-        int b;
-        do {} while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
-                                               b = blockedCount, b - 1));
-    }
-
-    /**
-     * Possibly blocks waiting for the given task to complete, or
-     * cancels the task if terminating.  Fails to wait if contended.
-     *
-     * @param joinMe the task
-     */
-    final void tryAwaitJoin(ForkJoinTask<?> joinMe) {
-        int s;
-        Thread.interrupted(); // clear interrupts before checking termination
-        if (joinMe.status >= 0) {
-            if (tryPreBlock()) {
-                joinMe.tryAwaitDone(0L);
-                postBlock();
-            }
-            else if ((ctl & STOP_BIT) != 0L)
-                joinMe.cancelIgnoringExceptions();
-        }
+        return stat;
     }
 
     /**
-     * Possibly blocks the given worker waiting for joinMe to
-     * complete or timeout
+     * If task is at base of some steal queue, steals and executes it.
      *
-     * @param joinMe the task
-     * @param millis the wait time for underlying Object.wait
-     */
-    final void timedAwaitJoin(ForkJoinTask<?> joinMe, long nanos) {
-        while (joinMe.status >= 0) {
-            Thread.interrupted();
-            if ((ctl & STOP_BIT) != 0L) {
-                joinMe.cancelIgnoringExceptions();
-                break;
-            }
-            if (tryPreBlock()) {
-                long last = System.nanoTime();
-                while (joinMe.status >= 0) {
-                    long millis = TimeUnit.NANOSECONDS.toMillis(nanos);
-                    if (millis <= 0)
-                        break;
-                    joinMe.tryAwaitDone(millis);
-                    if (joinMe.status < 0)
-                        break;
-                    if ((ctl & STOP_BIT) != 0L) {
-                        joinMe.cancelIgnoringExceptions();
-                        break;
-                    }
-                    long now = System.nanoTime();
-                    nanos -= now - last;
-                    last = now;
-                }
-                postBlock();
-                break;
-            }
-        }
-    }
-
-    /**
-     * If necessary, compensates for blocker, and blocks
-     */
-    private void awaitBlocker(ManagedBlocker blocker)
-        throws InterruptedException {
-        while (!blocker.isReleasable()) {
-            if (tryPreBlock()) {
-                try {
-                    do {} while (!blocker.isReleasable() && !blocker.block());
-                } finally {
-                    postBlock();
-                }
-                break;
-            }
-        }
-    }
-
-    // Creating, registering and deregistring workers
-
-    /**
-     * Tries to create and start a worker; minimally rolls back counts
-     * on failure.
+     * @param joiner the joining worker
+     * @param task the task
      */
-    private void addWorker() {
-        Throwable ex = null;
-        ForkJoinWorkerThread t = null;
-        try {
-            t = factory.newThread(this);
-        } catch (Throwable e) {
-            ex = e;
-        }
-        if (t == null) {  // null or exceptional factory return
-            long c;       // adjust counts
-            do {} while (!UNSAFE.compareAndSwapLong
-                         (this, ctlOffset, c = ctl,
-                          (((c - AC_UNIT) & AC_MASK) |
-                           ((c - TC_UNIT) & TC_MASK) |
-                           (c & ~(AC_MASK|TC_MASK)))));
-            // Propagate exception if originating from an external caller
-            if (!tryTerminate(false) && ex != null &&
-                !(Thread.currentThread() instanceof ForkJoinWorkerThread))
-                UNSAFE.throwException(ex);
-        }
-        else
-            t.start();
-    }
-
-    /**
-     * Callback from ForkJoinWorkerThread constructor to assign a
-     * public name
-     */
-    final String nextWorkerName() {
-        for (int n;;) {
-            if (UNSAFE.compareAndSwapInt(this, nextWorkerNumberOffset,
-                                         n = nextWorkerNumber, ++n))
-                return workerNamePrefix + n;
-        }
-    }
-
-    /**
-     * Callback from ForkJoinWorkerThread constructor to
-     * determine its poolIndex and record in workers array.
-     *
-     * @param w the worker
-     * @return the worker's pool index
-     */
-    final int registerWorker(ForkJoinWorkerThread w) {
-        /*
-         * In the typical case, a new worker acquires the lock, uses
-         * next available index and returns quickly.  Since we should
-         * not block callers (ultimately from signalWork or
-         * tryPreBlock) waiting for the lock needed to do this, we
-         * instead help release other workers while waiting for the
-         * lock.
-         */
-        for (int g;;) {
-            ForkJoinWorkerThread[] ws;
-            if (((g = scanGuard) & SG_UNIT) == 0 &&
-                UNSAFE.compareAndSwapInt(this, scanGuardOffset,
-                                         g, g | SG_UNIT)) {
-                int k = nextWorkerIndex;
-                try {
-                    if ((ws = workers) != null) { // ignore on shutdown
-                        int n = ws.length;
-                        if (k < 0 || k >= n || ws[k] != null) {
-                            for (k = 0; k < n && ws[k] != null; ++k)
-                                ;
-                            if (k == n)
-                                ws = workers = Arrays.copyOf(ws, n << 1);
-                        }
-                        ws[k] = w;
-                        nextWorkerIndex = k + 1;
-                        int m = g & SMASK;
-                        g = (k > m) ? ((m << 1) + 1) & SMASK : g + (SG_UNIT<<1);
-                    }
-                } finally {
-                    scanGuard = g;
-                }
-                return k;
-            }
-            else if ((ws = workers) != null) { // help release others
-                for (ForkJoinWorkerThread u : ws) {
-                    if (u != null && u.queueBase != u.queueTop) {
-                        if (tryReleaseWaiter())
-                            break;
-                    }
+    private void tryPollForAndExec(WorkQueue joiner, ForkJoinTask<?> task) {
+        WorkQueue[] ws;
+        if ((ws = workQueues) != null) {
+            for (int j = 1; j < ws.length && task.status >= 0; j += 2) {
+                WorkQueue q = ws[j];
+                if (q != null && q.pollFor(task)) {
+                    joiner.runSubtask(task);
+                    break;
                 }
             }
         }
     }
 
     /**
-     * Final callback from terminating worker.  Removes record of
-     * worker from array, and adjusts counts. If pool is shutting
-     * down, tries to complete termination.
+     * Tries to decrement active count (sometimes implicitly) and
+     * possibly release or create a compensating worker in preparation
+     * for blocking. Fails on contention or termination. Otherwise,
+     * adds a new thread if no idle workers are available and either
+     * pool would become completely starved or: (at least half
+     * starved, and fewer than 50% spares exist, and there is at least
+     * one task apparently available). Even though the availability
+     * check requires a full scan, it is worthwhile in reducing false
+     * alarms.
      *
-     * @param w the worker
+     * @param task if non-null, a task being waited for
+     * @param blocker if non-null, a blocker being waited for
+     * @return true if the caller can block, else should recheck and retry
      */
-    final void deregisterWorker(ForkJoinWorkerThread w, Throwable ex) {
-        int idx = w.poolIndex;
-        int sc = w.stealCount;
-        int steps = 0;
-        // Remove from array, adjust worker counts and collect steal count.
-        // We can intermix failed removes or adjusts with steal updates
-        do {
-            long s, c;
-            int g;
-            if (steps == 0 && ((g = scanGuard) & SG_UNIT) == 0 &&
-                UNSAFE.compareAndSwapInt(this, scanGuardOffset,
-                                         g, g |= SG_UNIT)) {
-                ForkJoinWorkerThread[] ws = workers;
-                if (ws != null && idx >= 0 &&
-                    idx < ws.length && ws[idx] == w)
-                    ws[idx] = null;    // verify
-                nextWorkerIndex = idx;
-                scanGuard = g + SG_UNIT;
-                steps = 1;
-            }
-            if (steps == 1 &&
-                UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
-                                          (((c - AC_UNIT) & AC_MASK) |
-                                           ((c - TC_UNIT) & TC_MASK) |
-                                           (c & ~(AC_MASK|TC_MASK)))))
-                steps = 2;
-            if (sc != 0 &&
-                UNSAFE.compareAndSwapLong(this, stealCountOffset,
-                                          s = stealCount, s + sc))
-                sc = 0;
-        } while (steps != 2 || sc != 0);
-        if (!tryTerminate(false)) {
-            if (ex != null)   // possibly replace if died abnormally
-                signalWork();
-            else
-                tryReleaseWaiter();
-        }
-    }
-
-    // Shutdown and termination
-
-    /**
-     * Possibly initiates and/or completes termination.
-     *
-     * @param now if true, unconditionally terminate, else only
-     * if shutdown and empty queue and no active workers
-     * @return true if now terminating or terminated
-     */
-    private boolean tryTerminate(boolean now) {
-        long c;
-        while (((c = ctl) & STOP_BIT) == 0) {
-            if (!now) {
-                if ((int)(c >> AC_SHIFT) != -parallelism)
-                    return false;
-                if (!shutdown || blockedCount != 0 || quiescerCount != 0 ||
-                    queueBase != queueTop) {
-                    if (ctl == c) // staleness check
-                        return false;
-                    continue;
+    final boolean tryCompensate(ForkJoinTask<?> task, ManagedBlocker blocker) {
+        int pc = parallelism, e;
+        long c = ctl;
+        WorkQueue[] ws = workQueues;
+        if ((e = (int)c) >= 0 && ws != null) {
+            int u, a, ac, hc;
+            int tc = (short)((u = (int)(c >>> 32)) >>> UTC_SHIFT) + pc;
+            boolean replace = false;
+            if ((a = u >> UAC_SHIFT) <= 0) {
+                if ((ac = a + pc) <= 1)
+                    replace = true;
+                else if ((e > 0 || (task != null &&
+                                    ac <= (hc = pc >>> 1) && tc < pc + hc))) {
+                    WorkQueue w;
+                    for (int j = 0; j < ws.length; ++j) {
+                        if ((w = ws[j]) != null && !w.isEmpty()) {
+                            replace = true;
+                            break;   // in compensation range and tasks available
+                        }
+                    }
                 }
             }
-            if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, c | STOP_BIT))
-                startTerminating();
-        }
-        if ((short)(c >>> TC_SHIFT) == -parallelism) { // signal when 0 workers
-            final ReentrantLock lock = this.submissionLock;
-            lock.lock();
-            try {
-                termination.signalAll();
-            } finally {
-                lock.unlock();
+            if ((task == null || task.status >= 0) && // recheck need to block
+                (blocker == null || !blocker.isReleasable()) && ctl == c) {
+                if (!replace) {          // no compensation
+                    long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
+                    if (U.compareAndSwapLong(this, CTL, c, nc))
+                        return true;
+                }
+                else if (e != 0) {       // release an idle worker
+                    WorkQueue w; Thread p; int i;
+                    if ((i = e & SMASK) < ws.length && (w = ws[i]) != null) {
+                        long nc = ((long)(w.nextWait & E_MASK) |
+                                   (c & (AC_MASK|TC_MASK)));
+                        if (w.eventCount == (e | INT_SIGN) &&
+                            U.compareAndSwapLong(this, CTL, c, nc)) {
+                            w.eventCount = (e + E_SEQ) & E_MASK;
+                            if ((p = w.parker) != null)
+                                U.unpark(p);
+                            return true;
+                        }
+                    }
+                }
+                else if (tc < MAX_CAP) { // create replacement
+                    long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
+                    if (U.compareAndSwapLong(this, CTL, c, nc)) {
+                        addWorker();
+                        return true;
+                    }
+                }
             }
         }
-        return true;
+        return false;
     }
 
     /**
-     * Runs up to three passes through workers: (0) Setting
-     * termination status for each worker, followed by wakeups up to
-     * queued workers; (1) helping cancel tasks; (2) interrupting
-     * lagging threads (likely in external tasks, but possibly also
-     * blocked in joins).  Each pass repeats previous steps because of
-     * potential lagging thread creation.
+     * Helps and/or blocks until the given task is done.
+     *
+     * @param joiner the joining worker
+     * @param task the task
+     * @return task status on exit
      */
-    private void startTerminating() {
-        cancelSubmissions();
-        for (int pass = 0; pass < 3; ++pass) {
-            ForkJoinWorkerThread[] ws = workers;
-            if (ws != null) {
-                for (ForkJoinWorkerThread w : ws) {
-                    if (w != null) {
-                        w.terminate = true;
-                        if (pass > 0) {
-                            w.cancelTasks();
-                            if (pass > 1 && !w.isInterrupted()) {
-                                try {
-                                    w.interrupt();
-                                } catch (SecurityException ignore) {
+    final int awaitJoin(WorkQueue joiner, ForkJoinTask<?> task) {
+        int s;
+        if ((s = task.status) >= 0) {
+            ForkJoinTask<?> prevJoin = joiner.currentJoin;
+            joiner.currentJoin = task;
+            long startTime = 0L;
+            for (int k = 0;;) {
+                if ((s = (joiner.isEmpty() ?           // try to help
+                          tryHelpStealer(joiner, task) :
+                          joiner.tryRemoveAndExec(task))) == 0 &&
+                    (s = task.status) >= 0) {
+                    if (k == 0) {
+                        startTime = System.nanoTime();
+                        tryPollForAndExec(joiner, task); // check uncommon case
+                    }
+                    else if ((k & (MAX_HELP - 1)) == 0 &&
+                             System.nanoTime() - startTime >=
+                             COMPENSATION_DELAY &&
+                             tryCompensate(task, null)) {
+                        if (task.trySetSignal()) {
+                            synchronized (task) {
+                                if (task.status >= 0) {
+                                    try {                // see ForkJoinTask
+                                        task.wait();     //  for explanation
+                                    } catch (InterruptedException ie) {
+                                    }
                                 }
+                                else
+                                    task.notifyAll();
                             }
                         }
+                        long c;                          // re-activate
+                        do {} while (!U.compareAndSwapLong
+                                     (this, CTL, c = ctl, c + AC_UNIT));
                     }
                 }
-                terminateWaiters();
+                if (s < 0 || (s = task.status) < 0) {
+                    joiner.currentJoin = prevJoin;
+                    break;
+                }
+                else if ((k++ & (MAX_HELP - 1)) == MAX_HELP >>> 1)
+                    Thread.yield();                     // for politeness
+            }
+        }
+        return s;
+    }
+
+    /**
+     * Stripped-down variant of awaitJoin used by timed joins. Tries
+     * to help join only while there is continuous progress. (Caller
+     * will then enter a timed wait.)
+     *
+     * @param joiner the joining worker
+     * @param task the task
+     * @return task status on exit
+     */
+    final int helpJoinOnce(WorkQueue joiner, ForkJoinTask<?> task) {
+        int s;
+        while ((s = task.status) >= 0 &&
+               (joiner.isEmpty() ?
+                tryHelpStealer(joiner, task) :
+                joiner.tryRemoveAndExec(task)) != 0)
+            ;
+        return s;
+    }
+
+    /**
+     * Returns a (probably) non-empty steal queue, if one is found
+     * during a random, then cyclic scan, else null.  This method must
+     * be retried by caller if, by the time it tries to use the queue,
+     * it is empty.
+     */
+    private WorkQueue findNonEmptyStealQueue(WorkQueue w) {
+        // Similar to loop in scan(), but ignoring submissions
+        int r = w.seed; r ^= r << 13; r ^= r >>> 17; w.seed = r ^= r << 5;
+        int step = (r >>> 16) | 1;
+        for (WorkQueue[] ws;;) {
+            int rs = runState, m;
+            if ((ws = workQueues) == null || (m = ws.length - 1) < 1)
+                return null;
+            for (int j = (m + 1) << 2; ; r += step) {
+                WorkQueue q = ws[((r << 1) | 1) & m];
+                if (q != null && !q.isEmpty())
+                    return q;
+                else if (--j < 0) {
+                    if (runState == rs)
+                        return null;
+                    break;
+                }
             }
         }
     }
 
+
     /**
-     * Polls and cancels all submissions. Called only during termination.
+     * Runs tasks until {@code isQuiescent()}. We piggyback on
+     * active count ctl maintenance, but rather than blocking
+     * when tasks cannot be found, we rescan until all others cannot
+     * find tasks either.
      */
-    private void cancelSubmissions() {
-        while (queueBase != queueTop) {
-            ForkJoinTask<?> task = pollSubmission();
-            if (task != null) {
-                try {
-                    task.cancel(false);
-                } catch (Throwable ignore) {
+    final void helpQuiescePool(WorkQueue w) {
+        for (boolean active = true;;) {
+            ForkJoinTask<?> localTask; // exhaust local queue
+            while ((localTask = w.nextLocalTask()) != null)
+                localTask.doExec();
+            WorkQueue q = findNonEmptyStealQueue(w);
+            if (q != null) {
+                ForkJoinTask<?> t; int b;
+                if (!active) {      // re-establish active count
+                    long c;
+                    active = true;
+                    do {} while (!U.compareAndSwapLong
+                                 (this, CTL, c = ctl, c + AC_UNIT));
+                }
+                if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
+                    w.runSubtask(t);
+            }
+            else {
+                long c;
+                if (active) {       // decrement active count without queuing
+                    active = false;
+                    do {} while (!U.compareAndSwapLong
+                                 (this, CTL, c = ctl, c -= AC_UNIT));
+                }
+                else
+                    c = ctl;        // re-increment on exit
+                if ((int)(c >> AC_SHIFT) + parallelism == 0) {
+                    do {} while (!U.compareAndSwapLong
+                                 (this, CTL, c = ctl, c + AC_UNIT));
+                    break;
                 }
             }
         }
     }
 
     /**
-     * Tries to set the termination status of waiting workers, and
-     * then wakes them up (after which they will terminate).
+     * Gets and removes a local or stolen task for the given worker.
+     *
+     * @return a task, if available
      */
-    private void terminateWaiters() {
-        ForkJoinWorkerThread[] ws = workers;
-        if (ws != null) {
-            ForkJoinWorkerThread w; long c; int i, e;
-            int n = ws.length;
-            while ((i = ~(e = (int)(c = ctl)) & SMASK) < n &&
-                   (w = ws[i]) != null && w.eventCount == (e & E_MASK)) {
-                if (UNSAFE.compareAndSwapLong(this, ctlOffset, c,
-                                              (long)(w.nextWait & E_MASK) |
-                                              ((c + AC_UNIT) & AC_MASK) |
-                                              (c & (TC_MASK|STOP_BIT)))) {
-                    w.terminate = true;
-                    w.eventCount = e + EC_UNIT;
-                    if (w.parked)
-                        UNSAFE.unpark(w);
-                }
-            }
+    final ForkJoinTask<?> nextTaskFor(WorkQueue w) {
+        for (ForkJoinTask<?> t;;) {
+            WorkQueue q; int b;
+            if ((t = w.nextLocalTask()) != null)
+                return t;
+            if ((q = findNonEmptyStealQueue(w)) == null)
+                return null;
+            if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
+                return t;
         }
     }
 
-    // misc ForkJoinWorkerThread support
-
-    /**
-     * Increment or decrement quiescerCount. Needed only to prevent
-     * triggering shutdown if a worker is transiently inactive while
-     * checking quiescence.
-     *
-     * @param delta 1 for increment, -1 for decrement
-     */
-    final void addQuiescerCount(int delta) {
-        int c;
-        do {} while (!UNSAFE.compareAndSwapInt(this, quiescerCountOffset,
-                                               c = quiescerCount, c + delta));
-    }
-
-    /**
-     * Directly increment or decrement active count without
-     * queuing. This method is used to transiently assert inactivation
-     * while checking quiescence.
-     *
-     * @param delta 1 for increment, -1 for decrement
-     */
-    final void addActiveCount(int delta) {
-        long d = delta < 0 ? -AC_UNIT : AC_UNIT;
-        long c;
-        do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
-                                                ((c + d) & AC_MASK) |
-                                                (c & ~AC_MASK)));
-    }
-
     /**
      * Returns the approximate (non-atomic) number of idle threads per
-     * active thread.
+     * active thread to offset steal queue size for method
+     * ForkJoinTask.getSurplusQueuedTaskCount().
      */
     final int idlePerActive() {
         // Approximate at powers of two for small values, saturate past 4
@@ -1395,6 +2020,91 @@
                 8);
     }
 
+    //  Termination
+
+    /**
+     * Possibly initiates and/or completes termination.  The caller
+     * triggering termination runs three passes through workQueues:
+     * (0) Setting termination status, followed by wakeups of queued
+     * workers; (1) cancelling all tasks; (2) interrupting lagging
+     * threads (likely in external tasks, but possibly also blocked in
+     * joins).  Each pass repeats previous steps because of potential
+     * lagging thread creation.
+     *
+     * @param now if true, unconditionally terminate, else only
+     * if no work and no active workers
+     * @param enable if true, enable shutdown when next possible
+     * @return true if now terminating or terminated
+     */
+    private boolean tryTerminate(boolean now, boolean enable) {
+        Mutex lock = this.lock;
+        for (long c;;) {
+            if (((c = ctl) & STOP_BIT) != 0) {      // already terminating
+                if ((short)(c >>> TC_SHIFT) == -parallelism) {
+                    lock.lock();                    // don't need try/finally
+                    termination.signalAll();        // signal when 0 workers
+                    lock.unlock();
+                }
+                return true;
+            }
+            if (runState >= 0) {                    // not yet enabled
+                if (!enable)
+                    return false;
+                lock.lock();
+                runState |= SHUTDOWN;
+                lock.unlock();
+            }
+            if (!now) {                             // check if idle & no tasks
+                if ((int)(c >> AC_SHIFT) != -parallelism ||
+                    hasQueuedSubmissions())
+                    return false;
+                // Check for unqueued inactive workers. One pass suffices.
+                WorkQueue[] ws = workQueues; WorkQueue w;
+                if (ws != null) {
+                    for (int i = 1; i < ws.length; i += 2) {
+                        if ((w = ws[i]) != null && w.eventCount >= 0)
+                            return false;
+                    }
+                }
+            }
+            if (U.compareAndSwapLong(this, CTL, c, c | STOP_BIT)) {
+                for (int pass = 0; pass < 3; ++pass) {
+                    WorkQueue[] ws = workQueues;
+                    if (ws != null) {
+                        WorkQueue w;
+                        int n = ws.length;
+                        for (int i = 0; i < n; ++i) {
+                            if ((w = ws[i]) != null) {
+                                w.runState = -1;
+                                if (pass > 0) {
+                                    w.cancelAll();
+                                    if (pass > 1)
+                                        w.interruptOwner();
+                                }
+                            }
+                        }
+                        // Wake up workers parked on event queue
+                        int i, e; long cc; Thread p;
+                        while ((e = (int)(cc = ctl) & E_MASK) != 0 &&
+                               (i = e & SMASK) < n &&
+                               (w = ws[i]) != null) {
+                            long nc = ((long)(w.nextWait & E_MASK) |
+                                       ((cc + AC_UNIT) & AC_MASK) |
+                                       (cc & (TC_MASK|STOP_BIT)));
+                            if (w.eventCount == (e | INT_SIGN) &&
+                                U.compareAndSwapLong(this, CTL, cc, nc)) {
+                                w.eventCount = (e + E_SEQ) & E_MASK;
+                                w.runState = -1;
+                                if ((p = w.parker) != null)
+                                    U.unpark(p);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+
     // Exported methods
 
     // Constructors
@@ -1464,29 +2174,31 @@
         checkPermission();
         if (factory == null)
             throw new NullPointerException();
-        if (parallelism <= 0 || parallelism > MAX_ID)
+        if (parallelism <= 0 || parallelism > MAX_CAP)
             throw new IllegalArgumentException();
         this.parallelism = parallelism;
         this.factory = factory;
         this.ueh = handler;
-        this.locallyFifo = asyncMode;
+        this.localMode = asyncMode ? FIFO_QUEUE : LIFO_QUEUE;
         long np = (long)(-parallelism); // offset ctl counts
         this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
-        this.submissionQueue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
-        // initialize workers array with room for 2*parallelism if possible
-        int n = parallelism << 1;
-        if (n >= MAX_ID)
-            n = MAX_ID;
-        else { // See Hackers Delight, sec 3.2, where n < (1 << 16)
-            n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8;
-        }
-        workers = new ForkJoinWorkerThread[n + 1];
-        this.submissionLock = new ReentrantLock();
-        this.termination = submissionLock.newCondition();
+        // Use nearest power 2 for workQueues size. See Hackers Delight sec 3.2.
+        int n = parallelism - 1;
+        n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; n |= n >>> 16;
+        int size = (n + 1) << 1;        // #slots = 2*#workers
+        this.submitMask = size - 1;     // room for max # of submit queues
+        this.workQueues = new WorkQueue[size];
+        this.termination = (this.lock = new Mutex()).newCondition();
+        this.stealCount = new AtomicLong();
+        this.nextWorkerNumber = new AtomicInteger();
+        int pn = poolNumberGenerator.incrementAndGet();
         StringBuilder sb = new StringBuilder("ForkJoinPool-");
-        sb.append(poolNumberGenerator.incrementAndGet());
+        sb.append(Integer.toString(pn));
         sb.append("-worker-");
         this.workerNamePrefix = sb.toString();
+        lock.lock();
+        this.runState = 1;              // set init flag
+        lock.unlock();
     }
 
     // Execution methods
@@ -1508,34 +2220,10 @@
      *         scheduled for execution
      */
     public <T> T invoke(ForkJoinTask<T> task) {
-        Thread t = Thread.currentThread();
         if (task == null)
             throw new NullPointerException();
-        if (shutdown)
-            throw new RejectedExecutionException();
-        if ((t instanceof ForkJoinWorkerThread) &&
-            ((ForkJoinWorkerThread)t).pool == this)
-            return task.invoke();  // bypass submit if in same pool
-        else {
-            addSubmission(task);
-            return task.join();
-        }
-    }
-
-    /**
-     * Unless terminating, forks task if within an ongoing FJ
-     * computation in the current pool, else submits as external task.
-     */
-    private <T> void forkOrSubmit(ForkJoinTask<T> task) {
-        ForkJoinWorkerThread w;
-        Thread t = Thread.currentThread();
-        if (shutdown)
-            throw new RejectedExecutionException();
-        if ((t instanceof ForkJoinWorkerThread) &&
-            (w = (ForkJoinWorkerThread)t).pool == this)
-            w.pushTask(task);
-        else
-            addSubmission(task);
+        doSubmit(task);
+        return task.join();
     }
 
     /**
@@ -1549,7 +2237,7 @@
     public void execute(ForkJoinTask<?> task) {
         if (task == null)
             throw new NullPointerException();
-        forkOrSubmit(task);
+        doSubmit(task);
     }
 
     // AbstractExecutorService methods
@@ -1566,8 +2254,8 @@
         if (task instanceof ForkJoinTask<?>) // avoid re-wrap
             job = (ForkJoinTask<?>) task;
         else
-            job = ForkJoinTask.adapt(task, null);
-        forkOrSubmit(job);
+            job = new ForkJoinTask.AdaptedRunnableAction(task);
+        doSubmit(job);
     }
 
     /**
@@ -1582,7 +2270,7 @@
     public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
         if (task == null)
             throw new NullPointerException();
-        forkOrSubmit(task);
+        doSubmit(task);
         return task;
     }
 
@@ -1592,10 +2280,8 @@
      *         scheduled for execution
      */
     public <T> ForkJoinTask<T> submit(Callable<T> task) {
-        if (task == null)
-            throw new NullPointerException();
-        ForkJoinTask<T> job = ForkJoinTask.adapt(task);
-        forkOrSubmit(job);
+        ForkJoinTask<T> job = new ForkJoinTask.AdaptedCallable<T>(task);
+        doSubmit(job);
         return job;
     }
 
@@ -1605,10 +2291,8 @@
      *         scheduled for execution
      */
     public <T> ForkJoinTask<T> submit(Runnable task, T result) {
-        if (task == null)
-            throw new NullPointerException();
-        ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
-        forkOrSubmit(job);
+        ForkJoinTask<T> job = new ForkJoinTask.AdaptedRunnable<T>(task, result);
+        doSubmit(job);
         return job;
     }
 
@@ -1624,8 +2308,8 @@
         if (task instanceof ForkJoinTask<?>) // avoid re-wrap
             job = (ForkJoinTask<?>) task;
         else
-            job = ForkJoinTask.adapt(task, null);
-        forkOrSubmit(job);
+            job = new ForkJoinTask.AdaptedRunnableAction(task);
+        doSubmit(job);
         return job;
     }
 
@@ -1634,25 +2318,31 @@
      * @throws RejectedExecutionException {@inheritDoc}
      */
     public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
-        ArrayList<ForkJoinTask<T>> forkJoinTasks =
-            new ArrayList<ForkJoinTask<T>>(tasks.size());
-        for (Callable<T> task : tasks)
-            forkJoinTasks.add(ForkJoinTask.adapt(task));
-        invoke(new InvokeAll<T>(forkJoinTasks));
-
+        // In previous versions of this class, this method constructed
+        // a task to run ForkJoinTask.invokeAll, but now external
+        // invocation of multiple tasks is at least as efficient.
+        List<ForkJoinTask<T>> fs = new ArrayList<ForkJoinTask<T>>(tasks.size());
+        // Workaround needed because method wasn't declared with
+        // wildcards in return type but should have been.
         @SuppressWarnings({"unchecked", "rawtypes"})
-            List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
-        return futures;
-    }
+            List<Future<T>> futures = (List<Future<T>>) (List) fs;
 
-    static final class InvokeAll<T> extends RecursiveAction {
-        final ArrayList<ForkJoinTask<T>> tasks;
-        InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; }
-        public void compute() {
-            try { invokeAll(tasks); }
-            catch (Exception ignore) {}
+        boolean done = false;
+        try {
+            for (Callable<T> t : tasks) {
+                ForkJoinTask<T> f = new ForkJoinTask.AdaptedCallable<T>(t);
+                doSubmit(f);
+                fs.add(f);
+            }
+            for (ForkJoinTask<T> f : fs)
+                f.quietlyJoin();
+            done = true;
+            return futures;
+        } finally {
+            if (!done)
+                for (ForkJoinTask<T> f : fs)
+                    f.cancel(false);
         }
-        private static final long serialVersionUID = -7914297376763021607L;
     }
 
     /**
@@ -1702,7 +2392,7 @@
      * @return {@code true} if this pool uses async mode
      */
     public boolean getAsyncMode() {
-        return locallyFifo;
+        return localMode != 0;
     }
 
     /**
@@ -1714,8 +2404,15 @@
      * @return the number of worker threads
      */
     public int getRunningThreadCount() {
-        int r = parallelism + (int)(ctl >> AC_SHIFT);
-        return (r <= 0) ? 0 : r; // suppress momentarily negative values
+        int rc = 0;
+        WorkQueue[] ws; WorkQueue w;
+        if ((ws = workQueues) != null) {
+            for (int i = 1; i < ws.length; i += 2) {
+                if ((w = ws[i]) != null && w.isApparentlyUnblocked())
+                    ++rc;
+            }
+        }
+        return rc;
     }
 
     /**
@@ -1726,7 +2423,7 @@
      * @return the number of active threads
      */
     public int getActiveThreadCount() {
-        int r = parallelism + (int)(ctl >> AC_SHIFT) + blockedCount;
+        int r = parallelism + (int)(ctl >> AC_SHIFT);
         return (r <= 0) ? 0 : r; // suppress momentarily negative values
     }
 
@@ -1742,7 +2439,7 @@
      * @return {@code true} if all threads are currently idle
      */
     public boolean isQuiescent() {
-        return parallelism + (int)(ctl >> AC_SHIFT) + blockedCount == 0;
+        return (int)(ctl >> AC_SHIFT) + parallelism == 0;
     }
 
     /**
@@ -1757,7 +2454,15 @@
      * @return the number of steals
      */
     public long getStealCount() {
-        return stealCount;
+        long count = stealCount.get();
+        WorkQueue[] ws; WorkQueue w;
+        if ((ws = workQueues) != null) {
+            for (int i = 1; i < ws.length; i += 2) {
+                if ((w = ws[i]) != null)
+                    count += w.totalSteals;
+            }
+        }
+        return count;
     }
 
     /**
@@ -1772,12 +2477,12 @@
      */
     public long getQueuedTaskCount() {
         long count = 0;
-        ForkJoinWorkerThread[] ws;
-        if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
-            (ws = workers) != null) {
-            for (ForkJoinWorkerThread w : ws)
-                if (w != null)
-                    count -= w.queueBase - w.queueTop; // must read base first
+        WorkQueue[] ws; WorkQueue w;
+        if ((ws = workQueues) != null) {
+            for (int i = 1; i < ws.length; i += 2) {
+                if ((w = ws[i]) != null)
+                    count += w.queueSize();
+            }
         }
         return count;
     }
@@ -1790,7 +2495,15 @@
      * @return the number of queued submissions
      */
     public int getQueuedSubmissionCount() {
-        return -queueBase + queueTop;
+        int count = 0;
+        WorkQueue[] ws; WorkQueue w;
+        if ((ws = workQueues) != null) {
+            for (int i = 0; i < ws.length; i += 2) {
+                if ((w = ws[i]) != null)
+                    count += w.queueSize();
+            }
+        }
+        return count;
     }
 
     /**
@@ -1800,7 +2513,14 @@
      * @return {@code true} if there are any queued submissions
      */
     public boolean hasQueuedSubmissions() {
-        return queueBase != queueTop;
+        WorkQueue[] ws; WorkQueue w;
+        if ((ws = workQueues) != null) {
+            for (int i = 0; i < ws.length; i += 2) {
+                if ((w = ws[i]) != null && !w.isEmpty())
+                    return true;
+            }
+        }
+        return false;
     }
 
     /**
@@ -1811,16 +2531,11 @@
      * @return the next submission, or {@code null} if none
      */
     protected ForkJoinTask<?> pollSubmission() {
-        ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
-        while ((b = queueBase) != queueTop &&
-               (q = submissionQueue) != null &&
-               (i = (q.length - 1) & b) >= 0) {
-            long u = (i << ASHIFT) + ABASE;
-            if ((t = q[i]) != null &&
-                queueBase == b &&
-                UNSAFE.compareAndSwapObject(q, u, t, null)) {
-                queueBase = b + 1;
-                return t;
+        WorkQueue[] ws; WorkQueue w; ForkJoinTask<?> t;
+        if ((ws = workQueues) != null) {
+            for (int i = 0; i < ws.length; i += 2) {
+                if ((w = ws[i]) != null && (t = w.poll()) != null)
+                    return t;
             }
         }
         return null;
@@ -1845,20 +2560,17 @@
      */
     protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
         int count = 0;
-        while (queueBase != queueTop) {
-            ForkJoinTask<?> t = pollSubmission();
-            if (t != null) {
-                c.add(t);
-                ++count;
+        WorkQueue[] ws; WorkQueue w; ForkJoinTask<?> t;
+        if ((ws = workQueues) != null) {
+            for (int i = 0; i < ws.length; ++i) {
+                if ((w = ws[i]) != null) {
+                    while ((t = w.poll()) != null) {
+                        c.add(t);
+                        ++count;
+                    }
+                }
             }
         }
-        ForkJoinWorkerThread[] ws;
-        if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
-            (ws = workers) != null) {
-            for (ForkJoinWorkerThread w : ws)
-                if (w != null)
-                    count += w.drainTasksTo(c);
-        }
         return count;
     }
 
@@ -1870,21 +2582,36 @@
      * @return a string identifying this pool, as well as its state
      */
     public String toString() {
-        long st = getStealCount();
-        long qt = getQueuedTaskCount();
-        long qs = getQueuedSubmissionCount();
-        int pc = parallelism;
+        // Use a single pass through workQueues to collect counts
+        long qt = 0L, qs = 0L; int rc = 0;
+        long st = stealCount.get();
         long c = ctl;
+        WorkQueue[] ws; WorkQueue w;
+        if ((ws = workQueues) != null) {
+            for (int i = 0; i < ws.length; ++i) {
+                if ((w = ws[i]) != null) {
+                    int size = w.queueSize();
+                    if ((i & 1) == 0)
+                        qs += size;
+                    else {
+                        qt += size;
+                        st += w.totalSteals;
+                        if (w.isApparentlyUnblocked())
+                            ++rc;
+                    }
+                }
+            }
+        }
+        int pc = parallelism;
         int tc = pc + (short)(c >>> TC_SHIFT);
-        int rc = pc + (int)(c >> AC_SHIFT);
-        if (rc < 0) // ignore transient negative
-            rc = 0;
-        int ac = rc + blockedCount;
+        int ac = pc + (int)(c >> AC_SHIFT);
+        if (ac < 0) // ignore transient negative
+            ac = 0;
         String level;
         if ((c & STOP_BIT) != 0)
             level = (tc == 0) ? "Terminated" : "Terminating";
         else
-            level = shutdown ? "Shutting down" : "Running";
+            level = runState < 0 ? "Shutting down" : "Running";
         return super.toString() +
             "[" + level +
             ", parallelism = " + pc +
@@ -1911,8 +2638,7 @@
      */
     public void shutdown() {
         checkPermission();
-        shutdown = true;
-        tryTerminate(false);
+        tryTerminate(false, true);
     }
 
     /**
@@ -1933,8 +2659,7 @@
      */
     public List<Runnable> shutdownNow() {
         checkPermission();
-        shutdown = true;
-        tryTerminate(true);
+        tryTerminate(true, true);
         return Collections.emptyList();
     }
 
@@ -1969,19 +2694,12 @@
     }
 
     /**
-     * Returns true if terminating or terminated. Used by ForkJoinWorkerThread.
-     */
-    final boolean isAtLeastTerminating() {
-        return (ctl & STOP_BIT) != 0L;
-    }
-
-    /**
      * Returns {@code true} if this pool has been shut down.
      *
      * @return {@code true} if this pool has been shut down
      */
     public boolean isShutdown() {
-        return shutdown;
+        return runState < 0;
     }
 
     /**
@@ -1998,7 +2716,7 @@
     public boolean awaitTermination(long timeout, TimeUnit unit)
         throws InterruptedException {
         long nanos = unit.toNanos(timeout);
-        final ReentrantLock lock = this.submissionLock;
+        final Mutex lock = this.lock;
         lock.lock();
         try {
             for (;;) {
@@ -2109,12 +2827,18 @@
     public static void managedBlock(ManagedBlocker blocker)
         throws InterruptedException {
         Thread t = Thread.currentThread();
-        if (t instanceof ForkJoinWorkerThread) {
-            ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
-            w.pool.awaitBlocker(blocker);
-        }
-        else {
-            do {} while (!blocker.isReleasable() && !blocker.block());
+        ForkJoinPool p = ((t instanceof ForkJoinWorkerThread) ?
+                          ((ForkJoinWorkerThread)t).pool : null);
+        while (!blocker.isReleasable()) {
+            if (p == null || p.tryCompensate(null, blocker)) {
+                try {
+                    do {} while (!blocker.isReleasable() && !blocker.block());
+                } finally {
+                    if (p != null)
+                        p.incrementActiveCount();
+                }
+                break;
+            }
         }
     }
 
@@ -2123,49 +2847,39 @@
     // implement RunnableFuture.
 
     protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
-        return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value);
+        return new ForkJoinTask.AdaptedRunnable<T>(runnable, value);
     }
 
     protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
-        return (RunnableFuture<T>) ForkJoinTask.adapt(callable);
+        return new ForkJoinTask.AdaptedCallable<T>(callable);
     }
 
     // Unsafe mechanics
-    private static final sun.misc.Unsafe UNSAFE;
-    private static final long ctlOffset;
-    private static final long stealCountOffset;
-    private static final long blockedCountOffset;
-    private static final long quiescerCountOffset;
-    private static final long scanGuardOffset;
-    private static final long nextWorkerNumberOffset;
-    private static final long ABASE;
+    private static final sun.misc.Unsafe U;
+    private static final long CTL;
+    private static final long PARKBLOCKER;
+    private static final int ABASE;
     private static final int ASHIFT;
 
     static {
         poolNumberGenerator = new AtomicInteger();
-        workerSeedGenerator = new Random();
+        nextSubmitterSeed = new AtomicInteger(0x55555555);
         modifyThreadPermission = new RuntimePermission("modifyThread");
         defaultForkJoinWorkerThreadFactory =
             new DefaultForkJoinWorkerThreadFactory();
+        submitters = new ThreadSubmitter();
         int s;
         try {
-            UNSAFE = sun.misc.Unsafe.getUnsafe();
+            U = sun.misc.Unsafe.getUnsafe();
             Class<?> k = ForkJoinPool.class;
-            ctlOffset = UNSAFE.objectFieldOffset
+            Class<?> ak = ForkJoinTask[].class;
+            CTL = U.objectFieldOffset
                 (k.getDeclaredField("ctl"));
-            stealCountOffset = UNSAFE.objectFieldOffset
-                (k.getDeclaredField("stealCount"));
-            blockedCountOffset = UNSAFE.objectFieldOffset
-                (k.getDeclaredField("blockedCount"));
-            quiescerCountOffset = UNSAFE.objectFieldOffset
-                (k.getDeclaredField("quiescerCount"));
-            scanGuardOffset = UNSAFE.objectFieldOffset
-                (k.getDeclaredField("scanGuard"));
-            nextWorkerNumberOffset = UNSAFE.objectFieldOffset
-                (k.getDeclaredField("nextWorkerNumber"));
-            Class<?> a = ForkJoinTask[].class;
-            ABASE = UNSAFE.arrayBaseOffset(a);
-            s = UNSAFE.arrayIndexScale(a);
+            Class<?> tk = Thread.class;
+            PARKBLOCKER = U.objectFieldOffset
+                (tk.getDeclaredField("parkBlocker"));
+            ABASE = U.arrayBaseOffset(ak);
+            s = U.arrayIndexScale(ak);
         } catch (Exception e) {
             throw new Error(e);
         }