OpenJDK / bsd-port / jdk9 / hotspot
changeset 8660:e532b042ad77
8087143: Reduce Symbol::_identity_hash to 2 bytes
Summary: Convert Symbol::_identity_hash from integer to short integer to save two bytes. Also change identity_hash() to have 'this' and first two bytes of symbol join the calculation.
Reviewed-by: iklam, coleenp, shade
| author | minqi |
|---|---|
| date | Mon, 29 Jun 2015 13:48:55 -0700 |
| parents | a51ca8e0d2f8 |
| children | 24e9c513dc27 00cd0f4c1172 |
| files | agent/src/share/classes/sun/jvm/hotspot/oops/Symbol.java src/share/vm/oops/symbol.cpp src/share/vm/oops/symbol.hpp src/share/vm/runtime/vmStructs.cpp |
| diffstat | 4 files changed, 19 insertions(+), 21 deletions(-) [+] |
line wrap: on
line diff
--- a/agent/src/share/classes/sun/jvm/hotspot/oops/Symbol.java Mon Jun 29 17:24:52 2015 +0000 +++ b/agent/src/share/classes/sun/jvm/hotspot/oops/Symbol.java Mon Jun 29 13:48:55 2015 -0700 @@ -47,7 +47,7 @@ Type type = db.lookupType("Symbol"); length = type.getCIntegerField("_length"); baseOffset = type.getField("_body").getOffset(); - idHash = type.getCIntegerField("_identity_hash"); + idHash = type.getJShortField("_identity_hash"); } // Format: @@ -81,9 +81,9 @@ return addr.getJByteAt(baseOffset + index); } - private static CIntegerField idHash; + private static JShortField idHash; - public int identityHash() { return (int)idHash.getValue(this.addr); } + public short identityHash() { return (short)idHash.getValue(this.addr); } public boolean equals(byte[] modUTF8Chars) { int l = (int) getLength();
--- a/src/share/vm/oops/symbol.cpp Mon Jun 29 17:24:52 2015 +0000 +++ b/src/share/vm/oops/symbol.cpp Mon Jun 29 13:48:55 2015 -0700 @@ -35,7 +35,7 @@ Symbol::Symbol(const u1* name, int length, int refcount) { _refcount = refcount; _length = length; - _identity_hash = os::random(); + _identity_hash = (short)os::random(); for (int i = 0; i < _length; i++) { byte_at_put(i, name[i]); }
--- a/src/share/vm/oops/symbol.hpp Mon Jun 29 17:24:52 2015 +0000 +++ b/src/share/vm/oops/symbol.hpp Mon Jun 29 13:48:55 2015 -0700 @@ -102,23 +102,18 @@ // type without virtual functions. class ClassLoaderData; -// We separate the fields in SymbolBase from Symbol::_body so that -// Symbol::size(int) can correctly calculate the space needed. -class SymbolBase : public MetaspaceObj { - public: +class Symbol : public MetaspaceObj { + friend class VMStructs; + friend class SymbolTable; + friend class MoveSymbols; + + private: ATOMIC_SHORT_PAIR( volatile short _refcount, // needs atomic operation unsigned short _length // number of UTF8 characters in the symbol (does not need atomic op) ); - int _identity_hash; -}; - -class Symbol : private SymbolBase { - friend class VMStructs; - friend class SymbolTable; - friend class MoveSymbols; - private: - jbyte _body[1]; + short _identity_hash; + jbyte _body[2]; enum { // max_symbol_length is constrained by type of _length @@ -126,7 +121,7 @@ }; static int size(int length) { - size_t sz = heap_word_size(sizeof(SymbolBase) + (length > 0 ? length : 0)); + size_t sz = heap_word_size(sizeof(Symbol) + (length > 2 ? length - 2 : 0)); return align_object_size(sz); } @@ -150,8 +145,11 @@ // Returns the largest size symbol we can safely hold. static int max_length() { return max_symbol_length; } - - int identity_hash() { return _identity_hash; } + unsigned identity_hash() { + unsigned addr_bits = (unsigned)((uintptr_t)this >> (LogMinObjAlignmentInBytes + 3)); + return (unsigned)_identity_hash | + ((addr_bits ^ (_length << 8) ^ (( _body[0] << 8) | _body[1])) << 16); + } // For symbol table alternate hashing unsigned int new_hash(juint seed);
--- a/src/share/vm/runtime/vmStructs.cpp Mon Jun 29 17:24:52 2015 +0000 +++ b/src/share/vm/runtime/vmStructs.cpp Mon Jun 29 13:48:55 2015 -0700 @@ -403,7 +403,7 @@ nonstatic_field(ObjArrayKlass, _element_klass, Klass*) \ nonstatic_field(ObjArrayKlass, _bottom_klass, Klass*) \ volatile_nonstatic_field(Symbol, _refcount, short) \ - nonstatic_field(Symbol, _identity_hash, int) \ + nonstatic_field(Symbol, _identity_hash, short) \ nonstatic_field(Symbol, _length, unsigned short) \ unchecked_nonstatic_field(Symbol, _body, sizeof(jbyte)) /* NOTE: no type */ \ nonstatic_field(TypeArrayKlass, _max_length, int) \