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