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/*
* Copyright (C) 2017 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/Condition.h>
#include <wtf/Lock.h>
namespace WTF {
// This is a traditional read-write lock implementation that enables concurrency between readers so long as
// the read critical section is long. Concurrent readers will experience contention on read().lock() and
// read().unlock() if the work inside the critical section is short. The more cores participate in reading,
// the longer the read critical section has to be for this locking scheme to be profitable.
class ReadWriteLock {
WTF_MAKE_NONCOPYABLE(ReadWriteLock);
WTF_MAKE_FAST_ALLOCATED;
public:
ReadWriteLock() = default;
// It's easiest to read lock like this:
//
// Locker locker { rwLock.read() };
//
// It's easiest to write lock like this:
//
// Locker locker { rwLock.write() };
//
WTF_EXPORT_PRIVATE void readLock();
WTF_EXPORT_PRIVATE void readUnlock();
WTF_EXPORT_PRIVATE void writeLock();
WTF_EXPORT_PRIVATE void writeUnlock();
class ReadLock;
class WriteLock;
ReadLock& read();
WriteLock& write();
private:
Lock m_lock;
Condition m_cond;
bool m_isWriteLocked WTF_GUARDED_BY_LOCK(m_lock) { false };
unsigned m_numReaders WTF_GUARDED_BY_LOCK(m_lock) { 0 };
unsigned m_numWaitingWriters WTF_GUARDED_BY_LOCK(m_lock) { 0 };
};
class ReadWriteLock::ReadLock : public ReadWriteLock {
public:
bool tryLock() { return false; }
void lock() { readLock(); }
void unlock() { readUnlock(); }
};
class ReadWriteLock::WriteLock : public ReadWriteLock {
public:
bool tryLock() { return false; }
void lock() { writeLock(); }
void unlock() { writeUnlock(); }
};
inline ReadWriteLock::ReadLock& ReadWriteLock::read() { return *static_cast<ReadLock*>(this); }
inline ReadWriteLock::WriteLock& ReadWriteLock::write() { return *static_cast<WriteLock*>(this); }
} // namespace WTF
using WTF::ReadWriteLock;
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