50ffd9921e
This uses slightly newer APIs from SkAtomics.h to make it a bit more efficient. No public API changes. TBR=reed@google.com BUG=skia: Review URL: https://codereview.chromium.org/1039323002
69 lines
2.1 KiB
C++
69 lines
2.1 KiB
C++
/*
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* Copyright 2015 Google Inc.
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*
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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#ifndef SkAtomics_sync_DEFINED
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#define SkAtomics_sync_DEFINED
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// This file is mostly a shim. We'd like to delete it. Please don't put much
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// effort into maintaining it, and if you find bugs in it, the right fix is to
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// delete this file and upgrade your compiler to something that supports
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// __atomic builtins or std::atomic.
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static inline void barrier(sk_memory_order mo) {
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asm volatile("" : : : "memory"); // Prevents the compiler from reordering code.
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#if SK_CPU_X86
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// On x86, we generally don't need an extra memory barrier for loads or stores.
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if (sk_memory_order_seq_cst == mo) { __sync_synchronize(); }
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#else
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// On other platforms (e.g. ARM) we do unless the memory order is relaxed.
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if (sk_memory_order_relaxed != mo) { __sync_synchronize(); }
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#endif
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}
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// These barriers only support our majority use cases: acquire and relaxed loads, release stores.
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// For anything more complicated, please consider deleting this file and upgrading your compiler.
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template <typename T>
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T sk_atomic_load(const T* ptr, sk_memory_order mo) {
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T val = *ptr;
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barrier(mo);
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return val;
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}
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template <typename T>
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void sk_atomic_store(T* ptr, T val, sk_memory_order mo) {
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barrier(mo);
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*ptr = val;
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}
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template <typename T>
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T sk_atomic_fetch_add(T* ptr, T val, sk_memory_order) {
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return __sync_fetch_and_add(ptr, val);
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}
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template <typename T>
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bool sk_atomic_compare_exchange(T* ptr, T* expected, T desired, sk_memory_order, sk_memory_order) {
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T prev = __sync_val_compare_and_swap(ptr, *expected, desired);
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if (prev == *expected) {
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return true;
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}
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*expected = prev;
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return false;
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}
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template <typename T>
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T sk_atomic_exchange(T* ptr, T val, sk_memory_order) {
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// There is no __sync exchange. Emulate it with a CAS loop.
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T prev;
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do {
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prev = sk_atomic_load(ptr);
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} while(!sk_atomic_compare_exchange(ptr, &prev, val));
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return prev;
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}
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#endif//SkAtomics_sync_DEFINED
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