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8009575: Reduce Symbol::_refcount from 4 bytes to 2 bytes

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Added Atomic::inc(short*) to support this change.

Reviewed-by: coleenp, dcubed, dholmes, minqi
This commit is contained in:
Ioi Lam 2013-06-23 22:08:28 -07:00
parent 1c281a9fb3
commit 196c8abc3d
5 changed files with 69 additions and 7 deletions
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22
hotspot/src/share/vm/runtime/atomic.hpp
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@ -64,11 +64,13 @@ class Atomic : AllStatic {
// Atomically increment location
inline static void inc (volatile jint* dest);
static void inc (volatile jshort* dest);
inline static void inc_ptr(volatile intptr_t* dest);
inline static void inc_ptr(volatile void* dest);
// Atomically decrement a location
inline static void dec (volatile jint* dest);
static void dec (volatile jshort* dest);
inline static void dec_ptr(volatile intptr_t* dest);
inline static void dec_ptr(volatile void* dest);
@ -95,4 +97,24 @@ class Atomic : AllStatic {
inline static void* cmpxchg_ptr(void* exchange_value, volatile void* dest, void* compare_value);
};
// To use Atomic::inc(jshort* dest) and Atomic::dec(jshort* dest), the address must be specially
// aligned, such that (*dest) occupies the upper 16 bits of an aligned 32-bit word. The best way to
// achieve is to place your short value next to another short value, which doesn't need atomic ops.
//
// Example
// ATOMIC_SHORT_PAIR(
// volatile short _refcount, // needs atomic operation
// unsigned short _length // number of UTF8 characters in the symbol (does not need atomic op)
// );
#ifdef VM_LITTLE_ENDIAN
#define ATOMIC_SHORT_PAIR(atomic_decl, non_atomic_decl) \
non_atomic_decl; \
atomic_decl
#else
#define ATOMIC_SHORT_PAIR(atomic_decl, non_atomic_decl) \
atomic_decl ; \
non_atomic_decl
#endif
#endif // SHARE_VM_RUNTIME_ATOMIC_HPP