109 lines
3.3 KiB
C++
109 lines
3.3 KiB
C++
/*
|
|
* 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;
|