src/share/vm/oops/symbol.hpp

@@ -100,35 +100,30 @@
 // This cannot be inherited from ResourceObj because it cannot have a vtable.
 // Since sometimes this is allocated from Metadata, pick a base allocation
 // 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:
-  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 {
+class Symbol : public MetaspaceObj {
   friend class VMStructs;
   friend class SymbolTable;
   friend class MoveSymbols;
+
  private:
-  jbyte _body[1];
+  ATOMIC_SHORT_PAIR(
+    volatile short _refcount,  // needs atomic operation
+    unsigned short _length     // number of UTF8 characters in the symbol (does not need atomic op)
+  );
+  short _identity_hash;
+  jbyte _body[2];
 
   enum {
     // max_symbol_length is constrained by type of _length
     max_symbol_length = (1 << 16) -1
   };
 
   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);
   }
 
   void byte_at_put(int index, int value) {
     assert(index >=0 && index < _length, "symbol index overflow");

@@ -148,12 +143,15 @@
 
   int size()                { return size(utf8_length()); }
 
   // 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);
 
   // Reference counting.  See comments above this class for when to use.