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