Source/WebCore/platform/GenericTaskQueue.h

/*
 * Copyright (C) 2015 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. 
 */

#ifndef GenericTaskQueue_h
#define GenericTaskQueue_h

#include "Timer.h"
#include <wtf/Deque.h>
#include <wtf/WeakPtr.h>

namespace WebCore {

template <typename T>
class TaskDispatcher {
public:
    TaskDispatcher(T& context)
        : m_context(context)
    {
    }

    void postTask(std::function<void()> f)
    {
        m_context.postTask(f);
    }

private:
    T& m_context;
};

template<>
class TaskDispatcher<Timer> {
public:
    TaskDispatcher()
        : m_timer(*this, &TaskDispatcher<Timer>::timerFired)
    {
    }

    void postTask(std::function<void()> function)
    {
        m_queue.append(function);
        m_timer.startOneShot(0);
    }

    void timerFired()
    {
        Deque<std::function<void()>> queue;
        queue.swap(m_queue);
        for (std::function<void()>& function : queue)
            function();
    }

    Timer m_timer;
    Deque<std::function<void()>> m_queue;
};

template <typename T>
class GenericTaskQueue {
public:
    GenericTaskQueue()
        : m_weakPtrFactory(this)
        , m_dispatcher()
    {
    }

    GenericTaskQueue(T& t)
        : m_weakPtrFactory(this)
        , m_dispatcher(t)
    {
    }

    typedef std::function<void()> TaskFunction;

    void enqueueTask(TaskFunction task)
    {
        if (m_isClosed)
            return;

        ++m_pendingTasks;
        auto weakThis = m_weakPtrFactory.createWeakPtr();
        m_dispatcher.postTask([weakThis, task] {
            if (!weakThis)
                return;
            ASSERT(weakThis->m_pendingTasks);
            --weakThis->m_pendingTasks;
            task();
        });
    }

    void close()
    {
        cancelAllTasks();
        m_isClosed = true;
    }

    void cancelAllTasks()
    {
        m_weakPtrFactory.revokeAll();
        m_pendingTasks = 0;
    }
    bool hasPendingTasks() const { return m_pendingTasks; }

private:
    WeakPtrFactory<GenericTaskQueue> m_weakPtrFactory;
    TaskDispatcher<T> m_dispatcher;
    unsigned m_pendingTasks { 0 };
    bool m_isClosed { false };
};

}

#endif