src/share/vm/runtime/atomic.hpp

rev 11200 : 8155949: Support relaxed semantics in cmpxchg
Reviewed-by:
Contributed-by: HORII@jp.ibm.com, mdoerr

@@ -25,10 +25,16 @@
 #ifndef SHARE_VM_RUNTIME_ATOMIC_HPP
 #define SHARE_VM_RUNTIME_ATOMIC_HPP
 
 #include "memory/allocation.hpp"
 
+typedef enum cmpxchg_cmpxchg_memory_order {
+  memory_order_relaxed,
+  // Use value which doesn't interfere with C++2011. We need to be more conservative.
+  memory_order_conservative = 8
+} cmpxchg_memory_order;
+
 class Atomic : AllStatic {
  private:
   static jbyte cmpxchg_general(jbyte exchange_value, volatile jbyte* dest, jbyte compare_value);
 
  public:

@@ -105,17 +111,17 @@
 
   // Performs atomic compare of *dest and compare_value, and exchanges
   // *dest with exchange_value if the comparison succeeded. Returns prior
   // value of *dest. cmpxchg*() provide:
   // <fence> compare-and-exchange <membar StoreLoad|StoreStore>
-  inline static jbyte    cmpxchg    (jbyte        exchange_value, volatile jbyte*        dest, jbyte        compare_value);
-  inline static jint     cmpxchg    (jint         exchange_value, volatile jint*         dest, jint         compare_value);
+  inline static jbyte    cmpxchg    (jbyte        exchange_value, volatile jbyte*        dest, jbyte        compare_value, cmpxchg_memory_order order = memory_order_conservative);
+  inline static jint     cmpxchg    (jint         exchange_value, volatile jint*         dest, jint         compare_value, cmpxchg_memory_order order = memory_order_conservative);
   // See comment above about using jlong atomics on 32-bit platforms
-  inline static jlong    cmpxchg    (jlong        exchange_value, volatile jlong*        dest, jlong        compare_value);
-  static unsigned int    cmpxchg    (unsigned int exchange_value, volatile unsigned int* dest, unsigned int compare_value);
-  inline static intptr_t cmpxchg_ptr(intptr_t     exchange_value, volatile intptr_t*     dest, intptr_t     compare_value);
-  inline static void*    cmpxchg_ptr(void*        exchange_value, volatile void*         dest, void*        compare_value);
+  inline static jlong    cmpxchg    (jlong        exchange_value, volatile jlong*        dest, jlong        compare_value, cmpxchg_memory_order order = memory_order_conservative);
+  static unsigned int    cmpxchg    (unsigned int exchange_value, volatile unsigned int* dest, unsigned int compare_value, cmpxchg_memory_order order = memory_order_conservative);
+  inline static intptr_t cmpxchg_ptr(intptr_t     exchange_value, volatile intptr_t*     dest, intptr_t     compare_value, cmpxchg_memory_order order = memory_order_conservative);
+  inline static void*    cmpxchg_ptr(void*        exchange_value, volatile void*         dest, void*        compare_value, cmpxchg_memory_order order = memory_order_conservative);
 };
 
 // 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.