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* Copyright 2015 Google Inc.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
#ifndef SkAtomics_sync_DEFINED
#define SkAtomics_sync_DEFINED
// This file is mostly a shim. We'd like to delete it. Please don't put much
// effort into maintaining it, and if you find bugs in it, the right fix is to
// delete this file and upgrade your compiler to something that supports
// __atomic builtins or std::atomic.
static inline void barrier(sk_memory_order mo) {
asm volatile("" : : : "memory"); // Prevents the compiler from reordering code.
#if SK_CPU_X86
// On x86, we generally don't need an extra memory barrier for loads or stores.
if (sk_memory_order_seq_cst == mo) { __sync_synchronize(); }
// On other platforms (e.g. ARM) we do unless the memory order is relaxed.
if (sk_memory_order_relaxed != mo) { __sync_synchronize(); }
// These barriers only support our majority use cases: acquire and relaxed loads, release stores.
// For anything more complicated, please consider deleting this file and upgrading your compiler.
template <typename T>
T sk_atomic_load(const T* ptr, sk_memory_order mo) {
T val = *ptr;
return val;
template <typename T>
void sk_atomic_store(T* ptr, T val, sk_memory_order mo) {
*ptr = val;
template <typename T>
T sk_atomic_fetch_add(T* ptr, T val, sk_memory_order) {
return __sync_fetch_and_add(ptr, val);
template <typename T>
bool sk_atomic_compare_exchange(T* ptr, T* expected, T desired, sk_memory_order, sk_memory_order) {
T prev = __sync_val_compare_and_swap(ptr, *expected, desired);
if (prev == *expected) {
return true;
*expected = prev;
return false;
template <typename T>
T sk_atomic_exchange(T* ptr, T val, sk_memory_order) {
// There is no __sync exchange. Emulate it with a CAS loop.
T prev;
do {
prev = sk_atomic_load(ptr);
} while(!sk_atomic_compare_exchange(ptr, &prev, val));
return prev;