// Copyright (c) 2006-2008 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/ref_counted.h directly instead. | |
#ifndef BASE_ATOMIC_REF_COUNT_H_ | |
#define BASE_ATOMIC_REF_COUNT_H_ | |
#include "base/atomicops.h" | |
#include "base/basictypes.h" | |
namespace base { | |
typedef base::subtle::Atomic32 AtomicRefCount; | |
// Increment a reference count by "increment", which must exceed 0. | |
inline void AtomicRefCountIncN(volatile AtomicRefCount *ptr, | |
AtomicRefCount increment) { | |
base::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) { | |
return base::subtle::Barrier_AtomicIncrement(ptr, -decrement) != 0; | |
} | |
// 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) { | |
return base::subtle::Acquire_Load(ptr) == 1; | |
} | |
// 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) { | |
return base::subtle::Acquire_Load(ptr) == 0; | |
} | |
} // namespace base | |
#endif // BASE_ATOMIC_REF_COUNT_H_ | |