Source/WTF/wtf/CancellableTask.h

/*
 * Copyright (C) 2021 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. 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 INC. OR ITS CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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 */

#pragma once

#include <wtf/Function.h>
#include <wtf/UniqueRef.h>
#include <wtf/WeakPtr.h>

namespace WTF {

class CancellableTask;

class TaskCancellationGroup : public CanMakeWeakPtr<TaskCancellationGroup> {
public:
    TaskCancellationGroup() : m_impl(makeUniqueRef<Impl>()) { }
    void cancel() { m_impl->cancel(); }
    bool hasPendingTask() const { return m_impl->hasPendingTask(); }

private:
    friend class CancellableTask;
    class Impl : public CanMakeWeakPtr<Impl> {
        WTF_MAKE_FAST_ALLOCATED;
    public:
        void cancel() { weakPtrFactory().revokeAll(); }
        bool hasPendingTask() const { return weakPtrFactory().weakPtrCount(); }
    };

    class Handle {
    public:
        bool isCancelled() const { return !m_impl; }
        void clear() { m_impl = nullptr; }
    private:
        friend class TaskCancellationGroup;
        explicit Handle(Impl& impl) : m_impl(impl) { }
        WeakPtr<Impl> m_impl;
    };
    Handle createHandle() { return Handle { m_impl }; }

    UniqueRef<Impl> m_impl;
};

class CancellableTask {
public:
    CancellableTask(TaskCancellationGroup&, Function<void()>&&);
    void operator()();

private:
    TaskCancellationGroup::Handle m_cancellationGroup;
    Function<void()> m_task;
};

inline CancellableTask::CancellableTask(TaskCancellationGroup& cancellationGroup, Function<void()>&& task)
    : m_cancellationGroup(cancellationGroup.createHandle())
    , m_task(WTFMove(task))
{ }

inline void CancellableTask::operator()()
{
    if (m_cancellationGroup.isCancelled())
        return;

    m_cancellationGroup.clear();
    m_task();
}

} // namespace WTF

using WTF::CancellableTask;
using WTF::TaskCancellationGroup;