atomic.hpp

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#ifndef SHARE_VM_RUNTIME_ATOMIC_HPP
#define SHARE_VM_RUNTIME_ATOMIC_HPP

#include "memory/allocation.hpp"

class Atomic : AllStatic {
 public:
  // Atomic operations on jlong types are not available on all 32-bit
  // platforms. If atomic ops on jlongs are defined here they must only
  // be used from code that verifies they are available at runtime and
  // can provide an alternative action if not - see supports_cx8() for
  // a means to test availability.

  // Atomically store to a location
  inline static void store    (jbyte    store_value, jbyte*    dest);
  inline static void store    (jshort   store_value, jshort*   dest);
  inline static void store    (jint     store_value, jint*     dest);
  // See comment above about using jlong atomics on 32-bit platforms
  inline static void store    (jlong    store_value, jlong*    dest);
  inline static void store_ptr(intptr_t store_value, intptr_t* dest);
  inline static void store_ptr(void*    store_value, void*     dest);

  inline static void store    (jbyte    store_value, volatile jbyte*    dest);
  inline static void store    (jshort   store_value, volatile jshort*   dest);
  inline static void store    (jint     store_value, volatile jint*     dest);
  // See comment above about using jlong atomics on 32-bit platforms
  inline static void store    (jlong    store_value, volatile jlong*    dest);
  inline static void store_ptr(intptr_t store_value, volatile intptr_t* dest);
  inline static void store_ptr(void*    store_value, volatile void*     dest);

  // See comment above about using jlong atomics on 32-bit platforms
  inline static jlong load(volatile jlong* src);

  // Atomically add to a location, return updated value
  inline static jint     add    (jint     add_value, volatile jint*     dest);
  inline static intptr_t add_ptr(intptr_t add_value, volatile intptr_t* dest);
  inline static void*    add_ptr(intptr_t add_value, volatile void*     dest);
  // See comment above about using jlong atomics on 32-bit platforms
         static jlong    add    (jlong    add_value, volatile jlong*    dest);

  // 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);

  // Performs atomic exchange of *dest with exchange_value.  Returns old prior value of *dest.
  inline static jint         xchg(jint         exchange_value, volatile jint*         dest);
         static unsigned int xchg(unsigned int exchange_value, volatile unsigned int* dest);

  inline static intptr_t xchg_ptr(intptr_t exchange_value, volatile intptr_t* dest);
  inline static void*    xchg_ptr(void*    exchange_value, volatile void*   dest);

  // Performs atomic compare of *dest and compare_value, and exchanges *dest with exchange_value
  // if the comparison succeeded.  Returns prior value of *dest.  Guarantees a two-way memory
  // barrier across the cmpxchg.  I.e., it's really a 'fence_cmpxchg_acquire'.
         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);
  // 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);
};

// 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