SkAtomic: always use std::atomic

include/ports/SkAtomics_atomic.h

-/*
- * 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_atomic_DEFINED
-#define SkAtomics_atomic_DEFINED
-
-template <typename T>
-T sk_atomic_load(const T* ptr, sk_memory_order mo) {
-    SkASSERT(mo == sk_memory_order_relaxed ||
-             mo == sk_memory_order_seq_cst ||
-             mo == sk_memory_order_acquire ||
-             mo == sk_memory_order_consume);
-    return __atomic_load_n(ptr, mo);
-}
-
-template <typename T>
-void sk_atomic_store(T* ptr, T val, sk_memory_order mo) {
-    SkASSERT(mo == sk_memory_order_relaxed ||
-             mo == sk_memory_order_seq_cst ||
-             mo == sk_memory_order_release);
-    __atomic_store_n(ptr, val, mo);
-}
-
-template <typename T>
-T sk_atomic_fetch_add(T* ptr, T val, sk_memory_order mo) {
-    // All values of mo are valid.
-    return __atomic_fetch_add(ptr, val, mo);
-}
-
-template <typename T>
-T sk_atomic_fetch_sub(T* ptr, T val, sk_memory_order mo) {
-    // All values of mo are valid.
-    return __atomic_fetch_sub(ptr, val, mo);
-}
-
-template <typename T>
-bool sk_atomic_compare_exchange(T* ptr, T* expected, T desired,
-                                sk_memory_order success,
-                                sk_memory_order failure) {
-    // All values of success are valid.
-    SkASSERT(failure == sk_memory_order_relaxed ||
-             failure == sk_memory_order_seq_cst ||
-             failure == sk_memory_order_acquire ||
-             failure == sk_memory_order_consume);
-    SkASSERT(failure <= success);
-    return __atomic_compare_exchange_n(ptr, expected, desired, false/*weak?*/, success, failure);
-}
-
-template <typename T>
-T sk_atomic_exchange(T* ptr, T val, sk_memory_order mo) {
-    // All values of mo are valid.
-    return __atomic_exchange_n(ptr, val, mo);
-}
-
-#endif//SkAtomics_atomic_DEFINED