base/atomicops_internals_gcc.h

// Copyright (c) 2009 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// This file is an internal atomic implementation, include base/atomicops.h
// instead. This file is for platforms that use GCC intrinsics rather than
// platform-specific assembly code for atomic operations.

#ifndef BASE_ATOMICOPS_INTERNALS_GCC_H_
#define BASE_ATOMICOPS_INTERNALS_GCC_H_

namespace base {
namespace subtle {

inline Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr,
                                         Atomic32 old_value,
                                         Atomic32 new_value) {
  Atomic32 prev_value;
  do {
    if (__sync_bool_compare_and_swap(ptr, old_value, new_value))
      return old_value;
    prev_value = *ptr;
  } while (prev_value == old_value);
  return prev_value;
}

inline Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr,
                                         Atomic32 new_value) {
  Atomic32 old_value;
  do {
    old_value = *ptr;
  } while (!__sync_bool_compare_and_swap(ptr, old_value, new_value));
  return old_value;
}

inline Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr,
                                          Atomic32 increment) {
  return Barrier_AtomicIncrement(ptr, increment);
}

inline Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr,
                                        Atomic32 increment) {
  for (;;) {
    // Atomic exchange the old value with an incremented one.
    Atomic32 old_value = *ptr;
    Atomic32 new_value = old_value + increment;
    if (__sync_bool_compare_and_swap(ptr, old_value, new_value)) {
      // The exchange took place as expected.
      return new_value;
    }
    // Otherwise, *ptr changed mid-loop and we need to retry.
  }
}

inline Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr,
                                       Atomic32 old_value,
                                       Atomic32 new_value) {
  // Since NoBarrier_CompareAndSwap uses __sync_bool_compare_and_swap, which
  // is a full memory barrier, none is needed here or below in Release.
  return NoBarrier_CompareAndSwap(ptr, old_value, new_value);
}

inline Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr,
                                       Atomic32 old_value,
                                       Atomic32 new_value) {
  return NoBarrier_CompareAndSwap(ptr, old_value, new_value);
}

inline void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value) {
  *ptr = value;
}

inline void MemoryBarrier() {
  __sync_synchronize();
}

inline void Acquire_Store(volatile Atomic32* ptr, Atomic32 value) {
  *ptr = value;
  MemoryBarrier();
}

inline void Release_Store(volatile Atomic32* ptr, Atomic32 value) {
  MemoryBarrier();
  *ptr = value;
}

inline Atomic32 NoBarrier_Load(volatile const Atomic32* ptr) {
  return *ptr;
}

inline Atomic32 Acquire_Load(volatile const Atomic32* ptr) {
  Atomic32 value = *ptr;
  MemoryBarrier();
  return value;
}

inline Atomic32 Release_Load(volatile const Atomic32* ptr) {
  MemoryBarrier();
  return *ptr;
}

}  // namespace base::subtle
}  // namespace base

#endif  // BASE_ATOMICOPS_INTERNALS_GCC_H_