root/Source/platform/ThreadTimers.cpp

DEFINITIONS

1. mainThreadSharedTimer
2. m_pendingSharedTimerFireTime
3. setSharedTimer
4. updateSharedTimer
5. sharedTimerFired
6. sharedTimerFiredInternal
7. fireTimersInNestedEventLoop

/*
 * Copyright (C) 2006, 2008 Apple Inc. All rights reserved.
 * Copyright (C) 2009 Google 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 COMPUTER, 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 COMPUTER, 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.
 */

#include "config.h"
#include "platform/ThreadTimers.h"

#include "platform/SharedTimer.h"
#include "platform/PlatformThreadData.h"
#include "platform/Timer.h"
#include "platform/TraceEvent.h"
#include "wtf/CurrentTime.h"
#include "wtf/MainThread.h"

using namespace std;

namespace WebCore {

// Fire timers for this length of time, and then quit to let the run loop process user input events.
// 100ms is about a perceptable delay in UI, so use a half of that as a threshold.
// This is to prevent UI freeze when there are too many timers or machine performance is low.
static const double maxDurationOfFiringTimers = 0.050;

// Timers are created, started and fired on the same thread, and each thread has its own ThreadTimers
// copy to keep the heap and a set of currently firing timers.

static MainThreadSharedTimer* mainThreadSharedTimer()
{
    static MainThreadSharedTimer* timer = new MainThreadSharedTimer;
    return timer;
}

ThreadTimers::ThreadTimers()
    : m_sharedTimer(0)
    , m_firingTimers(false)
    , m_pendingSharedTimerFireTime(0)
{
    if (isMainThread())
        setSharedTimer(mainThreadSharedTimer());
}

// A worker thread may initialize SharedTimer after some timers are created.
// Also, SharedTimer can be replaced with 0 before all timers are destroyed.
void ThreadTimers::setSharedTimer(SharedTimer* sharedTimer)
{
    if (m_sharedTimer) {
        m_sharedTimer->setFiredFunction(0);
        m_sharedTimer->stop();
        m_pendingSharedTimerFireTime = 0;
    }

    m_sharedTimer = sharedTimer;

    if (sharedTimer) {
        m_sharedTimer->setFiredFunction(ThreadTimers::sharedTimerFired);
        updateSharedTimer();
    }
}

void ThreadTimers::updateSharedTimer()
{
    if (!m_sharedTimer)
        return;

    if (m_firingTimers || m_timerHeap.isEmpty()) {
        m_pendingSharedTimerFireTime = 0;
        m_sharedTimer->stop();
    } else {
        double nextFireTime = m_timerHeap.first()->m_nextFireTime;
        double currentMonotonicTime = monotonicallyIncreasingTime();
        if (m_pendingSharedTimerFireTime) {
            // No need to restart the timer if both the pending fire time and the new fire time are in the past.
            if (m_pendingSharedTimerFireTime <= currentMonotonicTime && nextFireTime <= currentMonotonicTime)
                return;
        }
        m_pendingSharedTimerFireTime = nextFireTime;
        m_sharedTimer->setFireInterval(max(nextFireTime - currentMonotonicTime, 0.0));
    }
}

void ThreadTimers::sharedTimerFired()
{
    TRACE_EVENT_SET_SAMPLING_STATE("Blink", "BlinkInternal");

    // Redirect to non-static method.
    PlatformThreadData::current().threadTimers().sharedTimerFiredInternal();

    TRACE_EVENT_SET_SAMPLING_STATE("Blink", "Sleeping");
}

void ThreadTimers::sharedTimerFiredInternal()
{
    // Do a re-entrancy check.
    if (m_firingTimers)
        return;
    m_firingTimers = true;
    m_pendingSharedTimerFireTime = 0;

    double fireTime = monotonicallyIncreasingTime();
    double timeToQuit = fireTime + maxDurationOfFiringTimers;

    while (!m_timerHeap.isEmpty() && m_timerHeap.first()->m_nextFireTime <= fireTime) {
        TimerBase& timer = *m_timerHeap.first();
        timer.m_nextFireTime = 0;
        timer.m_unalignedNextFireTime = 0;
        timer.heapDeleteMin();

        double interval = timer.repeatInterval();
        timer.setNextFireTime(interval ? fireTime + interval : 0);

        TRACE_EVENT2("blink", "ThreadTimers::sharedTimerFiredInternal",
            "src_file", timer.location().fileName(),
            "src_func", timer.location().functionName());

        // Once the timer has been fired, it may be deleted, so do nothing else with it after this point.
        timer.fired();

        // Catch the case where the timer asked timers to fire in a nested event loop, or we are over time limit.
        if (!m_firingTimers || timeToQuit < monotonicallyIncreasingTime())
            break;
    }

    m_firingTimers = false;

    updateSharedTimer();
}

void ThreadTimers::fireTimersInNestedEventLoop()
{
    // Reset the reentrancy guard so the timers can fire again.
    m_firingTimers = false;
    updateSharedTimer();
}

} // namespace WebCore