// 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. // * 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 #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* 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 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); } #if defined(ARCH_CPU_64_BITS) typedef volatile std::atomic* 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 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); } #endif // defined(ARCH_CPU_64_BITS) } // namespace subtle } // namespace base #endif // BASE_ATOMICOPS_INTERNALS_PORTABLE_H_