cef/include/base/cef_atomic_ref_count.h

// Copyright (c) 2014 Marshall A. Greenblatt. Portions copyright (c) 2011
// Google Inc. All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//    * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//    * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//    * Neither the name of Google Inc. nor the name Chromium Embedded
// Framework nor the names of its contributors may be used to endorse
// or promote products derived from this software without specific prior
// written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// This is a low level implementation of atomic semantics for reference
// counting.  Please use cef_ref_counted.h directly instead.
//
// The Chromium implementation includes annotations to avoid some false
// positives when using data race detection tools. Annotations are not
// currently supported by the CEF implementation.

#ifndef CEF_INCLUDE_BASE_CEF_ATOMIC_REF_COUNT_H_
#define CEF_INCLUDE_BASE_CEF_ATOMIC_REF_COUNT_H_
#pragma once

#if defined(BASE_ATOMIC_REF_COUNT_H_)
// Do nothing if the Chromium header has already been included.
// This can happen in cases where Chromium code is used directly by the
// client application. When using Chromium code directly always include
// the Chromium header first to avoid type conflicts.
#elif defined(BUILDING_CEF_SHARED)
// When building CEF include the Chromium header directly.
#include "base/atomic_ref_count.h"
#else  // !BUILDING_CEF_SHARED
// The following is substantially similar to the Chromium implementation.
// If the Chromium implementation diverges the below implementation should be
// updated to match.

#include "include/base/cef_atomicops.h"

// Annotations are not currently supported.
#define ANNOTATE_HAPPENS_BEFORE(obj) /* empty */
#define ANNOTATE_HAPPENS_AFTER(obj) /* empty */

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  // !BUILDING_CEF_SHARED

#endif  // CEF_INCLUDE_BASE_CEF_ATOMIC_REF_COUNT_H_