/* * Copyright (C) 2008, 2013, 2016 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. * 3. Neither the name of Apple Inc. ("Apple") 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 APPLE AND ITS 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 APPLE OR ITS 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. */ #ifndef Locker_h #define Locker_h #include <wtf/Assertions.h> #include <wtf/Noncopyable.h> namespace WTF { enum NoLockingNecessaryTag { NoLockingNecessary }; class AbstractLocker { WTF_MAKE_NONCOPYABLE(AbstractLocker); public: AbstractLocker(NoLockingNecessaryTag) { } protected: AbstractLocker() { } }; template <typename T> class Locker : public AbstractLocker { public: explicit Locker(T& lockable) : m_lockable(&lockable) { lock(); } explicit Locker(T* lockable) : m_lockable(lockable) { lock(); } // You should be wary of using this constructor. It's only applicable // in places where there is a locking protocol for a particular object // but it's not necessary to engage in that protocol yet. For example, // this often happens when an object is newly allocated and it can not // be accessed concurrently. Locker(NoLockingNecessaryTag) : m_lockable(nullptr) { } Locker(int) = delete; ~Locker() { if (m_lockable) m_lockable->unlock(); } static Locker tryLock(T& lockable) { Locker result(NoLockingNecessary); if (lockable.tryLock()) { result.m_lockable = &lockable; return result; } return result; } explicit operator bool() const { return !!m_lockable; } void unlockEarly() { m_lockable->unlock(); m_lockable = 0; } // It's great to be able to pass lockers around. It enables custom locking adaptors like // JSC::LockDuringMarking. Locker(Locker&& other) : m_lockable(other.m_lockable) { other.m_lockable = nullptr; } Locker& operator=(Locker&& other) { if (m_lockable) m_lockable->unlock(); m_lockable = other.m_lockable; other.m_lockable = nullptr; return *this; } private: void lock() { if (m_lockable) m_lockable->lock(); } T* m_lockable; }; // Use this lock scope like so: // auto locker = holdLock(lock); template<typename LockType> Locker<LockType> holdLock(LockType& lock) { return Locker<LockType>(lock); } template<typename LockType> Locker<LockType> tryHoldLock(LockType& lock) { return Locker<LockType>::tryLock(lock); } } using WTF::AbstractLocker; using WTF::Locker; using WTF::NoLockingNecessaryTag; using WTF::NoLockingNecessary; using WTF::holdLock; #endif