text: // 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 subtle
  }  // namespace base
  
  #endif  // BASE_ATOMICOPS_INTERNALS_GCC_H_
  
  