Source/JavaScriptCore/heap/GCActivityCallback.cpp

/*
 * Copyright (C) 2010-2017 Apple Inc. All rights reserved.
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 *     notice, this list of conditions and the following disclaimer. 
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 *     its contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission. 
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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#include "config.h"
#include "GCActivityCallback.h"

#include "HeapInlines.h"
#include "JSLock.h"
#include "JSObject.h"
#include "VM.h"

namespace JSC {

bool GCActivityCallback::s_shouldCreateGCTimer = true;

const double timerSlop = 2.0; // Fudge factor to avoid performance cost of resetting timer.

GCActivityCallback::GCActivityCallback(Heap* heap)
    : GCActivityCallback(heap->vm())
{
}

void GCActivityCallback::doWork()
{
    Heap* heap = &m_vm->heap;
    if (!isEnabled())
        return;
    
    JSLockHolder locker(m_vm);
    if (heap->isDeferred()) {
        scheduleTimer(0_s);
        return;
    }

    doCollection();
}

#if USE(CF)
void GCActivityCallback::scheduleTimer(Seconds newDelay)
{
    if (newDelay * timerSlop > m_delay)
        return;
    Seconds delta = m_delay - newDelay;
    m_delay = newDelay;
    CFRunLoopTimerSetNextFireDate(m_timer.get(), CFRunLoopTimerGetNextFireDate(m_timer.get()) - delta.seconds());
}

void GCActivityCallback::cancelTimer()
{
    m_delay = s_decade;
    CFRunLoopTimerSetNextFireDate(m_timer.get(), CFAbsoluteTimeGetCurrent() + s_decade.seconds());
}

MonotonicTime GCActivityCallback::nextFireTime()
{
    return MonotonicTime::now() + Seconds(CFRunLoopTimerGetNextFireDate(m_timer.get()) - CFAbsoluteTimeGetCurrent());
}
#else
void GCActivityCallback::scheduleTimer(Seconds newDelay)
{
    if (newDelay * timerSlop > m_delay)
        return;
    Seconds delta = m_delay - newDelay;
    m_delay = newDelay;

    Seconds secondsUntilFire = m_timer.secondsUntilFire();
    m_timer.startOneShot(std::max<Seconds>(secondsUntilFire - delta, 0_s));
}

void GCActivityCallback::cancelTimer()
{
    m_delay = s_decade;
    m_timer.startOneShot(s_decade);
}

MonotonicTime GCActivityCallback::nextFireTime()
{
    return MonotonicTime::now() + m_timer.secondsUntilFire();
}
#endif

void GCActivityCallback::didAllocate(size_t bytes)
{
    // The first byte allocated in an allocation cycle will report 0 bytes to didAllocate. 
    // We pretend it's one byte so that we don't ignore this allocation entirely.
    if (!bytes)
        bytes = 1;
    double bytesExpectedToReclaim = static_cast<double>(bytes) * deathRate();
    Seconds newDelay = lastGCLength() / gcTimeSlice(bytesExpectedToReclaim);
    scheduleTimer(newDelay);
}

void GCActivityCallback::willCollect()
{
    cancelTimer();
}

void GCActivityCallback::cancel()
{
    cancelTimer();
}

}