ThreadTimers.cpp   [plain text]

/*
 * 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:
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 *    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
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#include "config.h"
#include "ThreadTimers.h"

#include "SharedTimer.h"
#include "ThreadGlobalData.h"
#include "Timer.h"
#include <wtf/CurrentTime.h>

#include "WebCoreThread.h"

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)
{
    // On iPhone WebKit, this is initialized from the main thread, but
    // isMainThread() checks for the Web Thread, and may not be initialized
    // when this method is called.
    if (isMainThread() || pthread_main_np())
        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_sharedTimer = sharedTimer;
    
    if (sharedTimer) {
        m_sharedTimer->setFiredFunction(ThreadTimers::sharedTimerFired);
        updateSharedTimer();
    }
}

void ThreadTimers::updateSharedTimer()
{
    if (!m_sharedTimer)
        return;
        
    if (m_firingTimers || m_timerHeap.isEmpty())
        m_sharedTimer->stop();
    else
        m_sharedTimer->setFireTime(m_timerHeap.first()->m_nextFireTime);
}

void ThreadTimers::sharedTimerFired()
{
    // Redirect to non-static method.
    threadGlobalData().threadTimers().sharedTimerFiredInternal();
}

void ThreadTimers::sharedTimerFiredInternal()
{
    ASSERT(WebThreadIsLocked() || !WebThreadIsEnabled());
    // Do a re-entrancy check.
    if (m_firingTimers)
        return;
    m_firingTimers = true;

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

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

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

        // 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 < currentTime())
            break;
    }

    m_firingTimers = false;

    updateSharedTimer();
}

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

} // namespace WebCore