Source/WTF/wtf/Locker.h

/*
 * 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
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 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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 * 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 };

template <typename T> class Locker {
    WTF_MAKE_NONCOPYABLE(Locker);
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();
    }
    
    void unlockEarly()
    {
        m_lockable->unlock();
        m_lockable = 0;
    }
private:
    void lock()
    {
        if (m_lockable)
            m_lockable->lock();
    }
    
    T* m_lockable;
};

}

using WTF::Locker;
using WTF::NoLockingNecessaryTag;
using WTF::NoLockingNecessary;

#endif