WTFSemaphore.h

/*
 * Copyright (C) 2018 Yusuke Suzuki <utatane.tea@gmail.com>.
 *
 * 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>
#include <wtf/Noncopyable.h>

namespace WTF {

class Semaphore final {
    WTF_MAKE_NONCOPYABLE(Semaphore);
    WTF_MAKE_FAST_ALLOCATED;
public:
    constexpr Semaphore(unsigned value)
        : m_value(value)
    {
    }

    void signal()
    {
        Locker locker { m_lock };
        m_value++;
        m_condition.notifyOne();
    }

    bool waitUntil(const TimeWithDynamicClockType& timeout)
    {
        Locker locker { m_lock };
        bool satisfied = m_condition.waitUntil(m_lock, timeout, [&] {
            assertIsHeld(m_lock);
            return m_value;
        });
        if (satisfied)
            --m_value;
        return satisfied;
    }

    bool waitFor(Seconds relativeTimeout)
    {
        return waitUntil(MonotonicTime::timePointFromNow(relativeTimeout));
    }

    void wait()
    {
        waitUntil(ParkingLot::Time::infinity());
    }

private:
    unsigned m_value WTF_GUARDED_BY_LOCK(m_lock) { 0 };
    Lock m_lock;
    Condition m_condition;
};


} // namespace WTF

using WTF::Semaphore;