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+// Copyright (c) 2014 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, use atomicops.h instead.
+//
+// This implementation uses C++11 atomics' member functions. The code base is
+// currently written assuming atomicity revolves around accesses instead of
+// C++11's memory locations. The burden is on the programmer to ensure that all
+// memory locations accessed atomically are never accessed non-atomically (tsan
+// should help with this).
+//
+// TODO(jfb) Modify the atomicops.h API and user code to declare atomic
+// locations as truly atomic. See the static_assert below.
+//
+// Of note in this implementation:
+// * All NoBarrier variants are implemented as relaxed.
+// * All Barrier variants are implemented as sequentially-consistent.
+// * Compare exchange's failure ordering is always the same as the success one
+// (except for release, which fails as relaxed): using a weaker ordering is
+// only valid under certain uses of compare exchange.
+// * Acquire store doesn't exist in the C11 memory model, it is instead
+// implemented as a relaxed store followed by a sequentially consistent
+// fence.
+// * Release load doesn't exist in the C11 memory model, it is instead
+// implemented as sequentially consistent fence followed by a relaxed load.
+// * Atomic increment is expected to return the post-incremented value, whereas
+// C11 fetch add returns the previous value. The implementation therefore
+// needs to increment twice (which the compiler should be able to detect and
+// optimize).
+
+#ifndef BASE_ATOMICOPS_INTERNALS_PORTABLE_H_
+#define BASE_ATOMICOPS_INTERNALS_PORTABLE_H_
+
+#include <atomic>
+
+#include "build/build_config.h"
+
+namespace base {
+namespace subtle {
+
+// This implementation is transitional and maintains the original API for
+// atomicops.h. This requires casting memory locations to the atomic types, and
+// assumes that the API and the C++11 implementation are layout-compatible,
+// which isn't true for all implementations or hardware platforms. The static
+// assertion should detect this issue, were it to fire then this header
+// shouldn't be used.
+//
+// TODO(jfb) If this header manages to stay committed then the API should be
+// modified, and all call sites updated.
+typedef volatile std::atomic<Atomic32>* AtomicLocation32;
+static_assert(sizeof(*(AtomicLocation32) nullptr) == sizeof(Atomic32),
+ "incompatible 32-bit atomic layout");
+
+inline Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr,
+ Atomic32 old_value,
+ Atomic32 new_value) {
+ ((AtomicLocation32)ptr)
+ ->compare_exchange_strong(old_value,
+ new_value,
+ std::memory_order_relaxed,
+ std::memory_order_relaxed);
+ return old_value;
+}
+
+inline Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr,
+ Atomic32 new_value) {
+ return ((AtomicLocation32)ptr)
+ ->exchange(new_value, std::memory_order_relaxed);
+}
+
+inline Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr,
+ Atomic32 increment) {
+ return increment +
+ ((AtomicLocation32)ptr)
+ ->fetch_add(increment, std::memory_order_relaxed);
+}
+
+inline Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr,
+ Atomic32 increment) {
+ return increment + ((AtomicLocation32)ptr)->fetch_add(increment);
+}
+
+inline Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr,
+ Atomic32 old_value,
+ Atomic32 new_value) {
+ ((AtomicLocation32)ptr)
+ ->compare_exchange_strong(old_value,
+ new_value,
+ std::memory_order_acquire,
+ std::memory_order_acquire);
+ return old_value;
+}
+
+inline Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr,
+ Atomic32 old_value,
+ Atomic32 new_value) {
+ ((AtomicLocation32)ptr)
+ ->compare_exchange_strong(old_value,
+ new_value,
+ std::memory_order_release,
+ std::memory_order_relaxed);
+ return old_value;
+}
+
+inline void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value) {
+ ((AtomicLocation32)ptr)->store(value, std::memory_order_relaxed);
+}
+
+inline void Acquire_Store(volatile Atomic32* ptr, Atomic32 value) {
+ ((AtomicLocation32)ptr)->store(value, std::memory_order_relaxed);
+ std::atomic_thread_fence(std::memory_order_seq_cst);
+}
+
+inline void Release_Store(volatile Atomic32* ptr, Atomic32 value) {
+ ((AtomicLocation32)ptr)->store(value, std::memory_order_release);
+}
+
+inline Atomic32 NoBarrier_Load(volatile const Atomic32* ptr) {
+ return ((AtomicLocation32)ptr)->load(std::memory_order_relaxed);
+}
+
+inline Atomic32 Acquire_Load(volatile const Atomic32* ptr) {
+ return ((AtomicLocation32)ptr)->load(std::memory_order_acquire);
+}
+
+inline Atomic32 Release_Load(volatile const Atomic32* ptr) {
+ std::atomic_thread_fence(std::memory_order_seq_cst);
+ return ((AtomicLocation32)ptr)->load(std::memory_order_relaxed);
+}
+
+#if defined(ARCH_CPU_64_BITS)
+
+typedef volatile std::atomic<Atomic64>* AtomicLocation64;
+static_assert(sizeof(*(AtomicLocation64) nullptr) == sizeof(Atomic64),
+ "incompatible 64-bit atomic layout");
+
+inline Atomic64 NoBarrier_CompareAndSwap(volatile Atomic64* ptr,
+ Atomic64 old_value,
+ Atomic64 new_value) {
+ ((AtomicLocation64)ptr)
+ ->compare_exchange_strong(old_value,
+ new_value,
+ std::memory_order_relaxed,
+ std::memory_order_relaxed);
+ return old_value;
+}
+
+inline Atomic64 NoBarrier_AtomicExchange(volatile Atomic64* ptr,
+ Atomic64 new_value) {
+ return ((AtomicLocation64)ptr)
+ ->exchange(new_value, std::memory_order_relaxed);
+}
+
+inline Atomic64 NoBarrier_AtomicIncrement(volatile Atomic64* ptr,
+ Atomic64 increment) {
+ return increment +
+ ((AtomicLocation64)ptr)
+ ->fetch_add(increment, std::memory_order_relaxed);
+}
+
+inline Atomic64 Barrier_AtomicIncrement(volatile Atomic64* ptr,
+ Atomic64 increment) {
+ return increment + ((AtomicLocation64)ptr)->fetch_add(increment);
+}
+
+inline Atomic64 Acquire_CompareAndSwap(volatile Atomic64* ptr,
+ Atomic64 old_value,
+ Atomic64 new_value) {
+ ((AtomicLocation64)ptr)
+ ->compare_exchange_strong(old_value,
+ new_value,
+ std::memory_order_acquire,
+ std::memory_order_acquire);
+ return old_value;
+}
+
+inline Atomic64 Release_CompareAndSwap(volatile Atomic64* ptr,
+ Atomic64 old_value,
+ Atomic64 new_value) {
+ ((AtomicLocation64)ptr)
+ ->compare_exchange_strong(old_value,
+ new_value,
+ std::memory_order_release,
+ std::memory_order_relaxed);
+ return old_value;
+}
+
+inline void NoBarrier_Store(volatile Atomic64* ptr, Atomic64 value) {
+ ((AtomicLocation64)ptr)->store(value, std::memory_order_relaxed);
+}
+
+inline void Acquire_Store(volatile Atomic64* ptr, Atomic64 value) {
+ ((AtomicLocation64)ptr)->store(value, std::memory_order_relaxed);
+ std::atomic_thread_fence(std::memory_order_seq_cst);
+}
+
+inline void Release_Store(volatile Atomic64* ptr, Atomic64 value) {
+ ((AtomicLocation64)ptr)->store(value, std::memory_order_release);
+}
+
+inline Atomic64 NoBarrier_Load(volatile const Atomic64* ptr) {
+ return ((AtomicLocation64)ptr)->load(std::memory_order_relaxed);
+}
+
+inline Atomic64 Acquire_Load(volatile const Atomic64* ptr) {
+ return ((AtomicLocation64)ptr)->load(std::memory_order_acquire);
+}
+
+inline Atomic64 Release_Load(volatile const Atomic64* ptr) {
+ std::atomic_thread_fence(std::memory_order_seq_cst);
+ return ((AtomicLocation64)ptr)->load(std::memory_order_relaxed);
+}
+
+#endif // defined(ARCH_CPU_64_BITS)
+} // namespace subtle
+} // namespace base
+
+#endif // BASE_ATOMICOPS_INTERNALS_PORTABLE_H_