| // 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_ |
| |
| #include "base/atomicops.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) { |
| bool res = (subtle::Barrier_AtomicIncrement(ptr, -decrement) != 0); |
| 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); |
| 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); |
| return res; |
| } |
| |
| } // namespace base |
| |
| #endif // BASE_ATOMIC_REF_COUNT_H_ |