Source/WebCore/platform/ThreadTimers.cpp

/*
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 * Copyright (C) 2009 Google Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
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#include "config.h"
#include "ThreadTimers.h"

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

#if PLATFORM(IOS)
#include "WebCoreThread.h"
#endif

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 Seconds maxDurationOfFiringTimers { 50_ms };

// 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.

ThreadTimers::ThreadTimers()
{
    if (isUIThread())
        setSharedTimer(&MainThreadSharedTimer::singleton());
}

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

void ThreadTimers::updateSharedTimer()
{
    if (!m_sharedTimer)
        return;
        
    if (m_firingTimers || m_timerHeap.isEmpty()) {
        m_pendingSharedTimerFireTime = MonotonicTime { };
        m_sharedTimer->stop();
    } else {
        MonotonicTime nextFireTime = m_timerHeap.first()->m_nextFireTime;
        MonotonicTime currentMonotonicTime = MonotonicTime::now();
        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(std::max(nextFireTime - currentMonotonicTime, 0_s));
    }
}

void ThreadTimers::sharedTimerFiredInternal()
{
    ASSERT(isMainThread() || (!isWebThread() && !isUIThread()));
    // Do a re-entrancy check.
    if (m_firingTimers)
        return;
    m_firingTimers = true;
    m_pendingSharedTimerFireTime = MonotonicTime { };

    MonotonicTime fireTime = MonotonicTime::now();
    MonotonicTime timeToQuit = fireTime + maxDurationOfFiringTimers;

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

        Seconds interval = timer->repeatInterval();
        timer->setNextFireTime(interval ? fireTime + interval : MonotonicTime { });

        // 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 < MonotonicTime::now())
            break;
    }

    m_firingTimers = false;

    updateSharedTimer();
}

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

    if (m_sharedTimer) {
        m_sharedTimer->invalidate();
        m_pendingSharedTimerFireTime = MonotonicTime { };
    }

    updateSharedTimer();
}

} // namespace WebCore