| /* |
| * Copyright (C) 2015-2019 Apple 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: |
| * 1. Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * 2. 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. |
| * |
| * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``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 APPLE INC. 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. |
| */ |
| |
| #pragma once |
| |
| #include <wtf/Atomics.h> |
| #include <wtf/Compiler.h> |
| #include <wtf/Locker.h> |
| #include <wtf/Noncopyable.h> |
| |
| namespace TestWebKitAPI { |
| struct LockInspector; |
| }; |
| |
| namespace WTF { |
| |
| // A WordLock is a fully adaptive mutex that uses sizeof(void*) storage. It has a fast path that is |
| // similar to a spinlock, and a slow path that is similar to std::mutex. In most cases, you should use |
| // Lock instead. WordLock sits lower in the stack and is used to implement Lock, so Lock is the main |
| // client of WordLock. |
| |
| // NOTE: This is also a great lock to use if you are very low in the stack. For example, |
| // PrintStream uses this so that ParkingLot and Lock can use PrintStream. This means that if you |
| // try to use dataLog to debug this code, you will have a bad time. |
| |
| class WordLock final { |
| WTF_MAKE_NONCOPYABLE(WordLock); |
| WTF_MAKE_FAST_ALLOCATED; |
| public: |
| constexpr WordLock() = default; |
| |
| void lock() |
| { |
| if (LIKELY(m_word.compareExchangeWeak(0, isLockedBit, std::memory_order_acquire))) { |
| // WordLock acquired! |
| return; |
| } |
| |
| lockSlow(); |
| } |
| |
| void unlock() |
| { |
| if (LIKELY(m_word.compareExchangeWeak(isLockedBit, 0, std::memory_order_release))) { |
| // WordLock released, and nobody was waiting! |
| return; |
| } |
| |
| unlockSlow(); |
| } |
| |
| bool isHeld() const |
| { |
| return m_word.load(std::memory_order_acquire) & isLockedBit; |
| } |
| |
| bool isLocked() const |
| { |
| return isHeld(); |
| } |
| |
| protected: |
| friend struct TestWebKitAPI::LockInspector; |
| |
| static constexpr uintptr_t isLockedBit = 1; |
| static constexpr uintptr_t isQueueLockedBit = 2; |
| static constexpr uintptr_t queueHeadMask = 3; |
| |
| WTF_EXPORT_PRIVATE void lockSlow(); |
| WTF_EXPORT_PRIVATE void unlockSlow(); |
| |
| // Method used for testing only. |
| bool isFullyReset() const |
| { |
| return !m_word.load(); |
| } |
| |
| Atomic<uintptr_t> m_word { 0 }; |
| }; |
| |
| using WordLockHolder = Locker<WordLock>; |
| |
| } // namespace WTF |
| |
| using WTF::WordLock; |
| using WTF::WordLockHolder; |