atomic_ref_count.h revision c407dc5cd9bdc5668497f21b26b09d988ab439de
1c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved. 2c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// Use of this source code is governed by a BSD-style license that can be 3c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// found in the LICENSE file. 4c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott 5c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// This is a low level implementation of atomic semantics for reference 6c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// counting. Please use base/ref_counted.h directly instead. 7c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// 8c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// The implementation includes annotations to avoid some false positives 9c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// when using data race detection tools. 10c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott 11c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott#ifndef BASE_ATOMIC_REF_COUNT_H_ 12c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott#define BASE_ATOMIC_REF_COUNT_H_ 13c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott 14c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott#include "base/atomicops.h" 15c407dc5cd9bdc5668497f21b26b09d988ab439deBen Murdoch#include "base/third_party/dynamic_annotations/dynamic_annotations.h" 16c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott 17c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scottnamespace base { 18c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott 19c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scotttypedef subtle::Atomic32 AtomicRefCount; 20c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott 21c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// Increment a reference count by "increment", which must exceed 0. 22c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scottinline void AtomicRefCountIncN(volatile AtomicRefCount *ptr, 23c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott AtomicRefCount increment) { 24c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott subtle::NoBarrier_AtomicIncrement(ptr, increment); 25c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott} 26c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott 27c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// Decrement a reference count by "decrement", which must exceed 0, 28c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// and return whether the result is non-zero. 29c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// Insert barriers to ensure that state written before the reference count 30c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// became zero will be visible to a thread that has just made the count zero. 31c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scottinline bool AtomicRefCountDecN(volatile AtomicRefCount *ptr, 32c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott AtomicRefCount decrement) { 33c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott ANNOTATE_HAPPENS_BEFORE(ptr); 34c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott bool res = (subtle::Barrier_AtomicIncrement(ptr, -decrement) != 0); 35c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott if (!res) { 36c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott ANNOTATE_HAPPENS_AFTER(ptr); 37c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott } 38c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott return res; 39c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott} 40c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott 41c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// Increment a reference count by 1. 42c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scottinline void AtomicRefCountInc(volatile AtomicRefCount *ptr) { 43c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott base::AtomicRefCountIncN(ptr, 1); 44c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott} 45c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott 46c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// Decrement a reference count by 1 and return whether the result is non-zero. 47c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// Insert barriers to ensure that state written before the reference count 48c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// became zero will be visible to a thread that has just made the count zero. 49c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scottinline bool AtomicRefCountDec(volatile AtomicRefCount *ptr) { 50c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott return base::AtomicRefCountDecN(ptr, 1); 51c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott} 52c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott 53c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// Return whether the reference count is one. If the reference count is used 54c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// in the conventional way, a refrerence count of 1 implies that the current 55c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// thread owns the reference and no other thread shares it. This call performs 56c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// the test for a reference count of one, and performs the memory barrier 57c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// needed for the owning thread to act on the object, knowing that it has 58c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// exclusive access to the object. 59c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scottinline bool AtomicRefCountIsOne(volatile AtomicRefCount *ptr) { 60c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott bool res = (subtle::Acquire_Load(ptr) == 1); 61c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott if (res) { 62c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott ANNOTATE_HAPPENS_AFTER(ptr); 63c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott } 64c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott return res; 65c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott} 66c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott 67c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// Return whether the reference count is zero. With conventional object 68c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// referencing counting, the object will be destroyed, so the reference count 69c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott// should never be zero. Hence this is generally used for a debug check. 70c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scottinline bool AtomicRefCountIsZero(volatile AtomicRefCount *ptr) { 71c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott bool res = (subtle::Acquire_Load(ptr) == 0); 72c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott if (res) { 73c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott ANNOTATE_HAPPENS_AFTER(ptr); 74c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott } 75c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott return res; 76c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott} 77c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott 78c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott} // namespace base 79c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott 80c7f5f8508d98d5952d42ed7648c2a8f30a4da156Patrick Scott#endif // BASE_ATOMIC_REF_COUNT_H_ 81