| // 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(USING_CHROMIUM_INCLUDES) |
| // When building CEF include the Chromium header directly. |
| #include "base/atomic_ref_count.h" |
| |
| #else // !USING_CHROMIUM_INCLUDES |
| // The following is substantially similar to the Chromium implementation. |
| // If the Chromium implementation diverges the below implementation should be |
| // updated to match. |
| |
| #include <atomic> |
| |
| namespace base { |
| |
| class AtomicRefCount { |
| public: |
| constexpr AtomicRefCount() : ref_count_(0) {} |
| explicit constexpr AtomicRefCount(int initial_value) |
| : ref_count_(initial_value) {} |
| |
| /// |
| /// Increment a reference count. |
| /// Returns the previous value of the count. |
| /// |
| int Increment() { return Increment(1); } |
| |
| /// |
| /// Increment a reference count by "increment", which must exceed 0. |
| /// Returns the previous value of the count. |
| /// |
| int Increment(int increment) { |
| return ref_count_.fetch_add(increment, std::memory_order_relaxed); |
| } |
| |
| /// |
| /// Decrement a reference count, 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. |
| /// |
| bool Decrement() { |
| // TODO(jbroman): Technically this doesn't need to be an acquire operation |
| // unless the result is 1 (i.e., the ref count did indeed reach zero). |
| // However, there are toolchain issues that make that not work as well at |
| // present (notably TSAN doesn't like it). |
| return ref_count_.fetch_sub(1, std::memory_order_acq_rel) != 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. |
| /// |
| bool IsOne() const { return ref_count_.load(std::memory_order_acquire) == 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. |
| /// |
| bool IsZero() const { |
| return ref_count_.load(std::memory_order_acquire) == 0; |
| } |
| |
| /// |
| /// Returns the current reference count (with no barriers). This is subtle, |
| /// and should be used only for debugging. |
| /// |
| int SubtleRefCountForDebug() const { |
| return ref_count_.load(std::memory_order_relaxed); |
| } |
| |
| private: |
| std::atomic_int ref_count_; |
| }; |
| |
| } // namespace base |
| |
| #endif // !USING_CHROMIUM_INCLUDES |
| |
| #endif // CEF_INCLUDE_BASE_CEF_ATOMIC_REF_COUNT_H_ |