81 lines
2.9 KiB
C++
81 lines
2.9 KiB
C++
// Copyright (c) 2011 The Chromium Authors. All rights reserved.
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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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// This is a low level implementation of atomic semantics for reference
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// counting. Please use base/memory/ref_counted.h directly instead.
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//
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// The implementation includes annotations to avoid some false positives
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// when using data race detection tools.
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#ifndef BASE_ATOMIC_REF_COUNT_H_
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#define BASE_ATOMIC_REF_COUNT_H_
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#include "base/atomicops.h"
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#include "base/third_party/dynamic_annotations/dynamic_annotations.h"
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namespace base {
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typedef subtle::Atomic32 AtomicRefCount;
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// Increment a reference count by "increment", which must exceed 0.
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inline void AtomicRefCountIncN(volatile AtomicRefCount *ptr,
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AtomicRefCount increment) {
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subtle::NoBarrier_AtomicIncrement(ptr, increment);
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}
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// Decrement a reference count by "decrement", which must exceed 0,
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// and return whether the result is non-zero.
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// Insert barriers to ensure that state written before the reference count
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// became zero will be visible to a thread that has just made the count zero.
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inline bool AtomicRefCountDecN(volatile AtomicRefCount *ptr,
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AtomicRefCount decrement) {
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ANNOTATE_HAPPENS_BEFORE(ptr);
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bool res = (subtle::Barrier_AtomicIncrement(ptr, -decrement) != 0);
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if (!res) {
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ANNOTATE_HAPPENS_AFTER(ptr);
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}
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return res;
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}
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// Increment a reference count by 1.
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inline void AtomicRefCountInc(volatile AtomicRefCount *ptr) {
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base::AtomicRefCountIncN(ptr, 1);
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}
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// Decrement a reference count by 1 and return whether the result is non-zero.
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// Insert barriers to ensure that state written before the reference count
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// became zero will be visible to a thread that has just made the count zero.
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inline bool AtomicRefCountDec(volatile AtomicRefCount *ptr) {
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return base::AtomicRefCountDecN(ptr, 1);
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}
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// Return whether the reference count is one. If the reference count is used
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// in the conventional way, a refrerence count of 1 implies that the current
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// thread owns the reference and no other thread shares it. This call performs
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// the test for a reference count of one, and performs the memory barrier
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// needed for the owning thread to act on the object, knowing that it has
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// exclusive access to the object.
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inline bool AtomicRefCountIsOne(volatile AtomicRefCount *ptr) {
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bool res = (subtle::Acquire_Load(ptr) == 1);
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if (res) {
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ANNOTATE_HAPPENS_AFTER(ptr);
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}
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return res;
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}
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// Return whether the reference count is zero. With conventional object
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// referencing counting, the object will be destroyed, so the reference count
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// should never be zero. Hence this is generally used for a debug check.
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inline bool AtomicRefCountIsZero(volatile AtomicRefCount *ptr) {
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bool res = (subtle::Acquire_Load(ptr) == 0);
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if (res) {
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ANNOTATE_HAPPENS_AFTER(ptr);
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}
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return res;
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}
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} // namespace base
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#endif // BASE_ATOMIC_REF_COUNT_H_
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