base/atomicops_internals_portable.h - platform/external/libchrome - Gitiles

 // 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>

 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 void MemoryBarrier() {
 #if defined(__GLIBCXX__)
   // Work around libstdc++ bug 51038 where atomic_thread_fence was declared but
   // not defined, leading to the linker complaining about undefined references.
   __atomic_thread_fence(std::memory_order_seq_cst);
 #else
   std::atomic_thread_fence(std::memory_order_seq_cst);
 #endif
 }

 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);
   MemoryBarrier();
 }

 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) {
   MemoryBarrier();
   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);
   MemoryBarrier();
 }

 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) {
   MemoryBarrier();
   return ((AtomicLocation64)ptr)->load(std::memory_order_relaxed);
 }

 #endif  // defined(ARCH_CPU_64_BITS)
 }  // namespace subtle
 }  // namespace base

 #endif  // BASE_ATOMICOPS_INTERNALS_PORTABLE_H_
	// 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>

	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 void MemoryBarrier() {
	#if defined(__GLIBCXX__)
	// Work around libstdc++ bug 51038 where atomic_thread_fence was declared but
	// not defined, leading to the linker complaining about undefined references.
	__atomic_thread_fence(std::memory_order_seq_cst);
	#else
	std::atomic_thread_fence(std::memory_order_seq_cst);
	#endif
	}

	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);
	MemoryBarrier();
	}

	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) {
	MemoryBarrier();
	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);
	MemoryBarrier();
	}

	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) {
	MemoryBarrier();
	return ((AtomicLocation64)ptr)->load(std::memory_order_relaxed);
	}

	#endif // defined(ARCH_CPU_64_BITS)
	} // namespace subtle
	} // namespace base

	#endif // BASE_ATOMICOPS_INTERNALS_PORTABLE_H_