Source/JavaScriptCore/heap/GCActivityCallback.cpp

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#include "config.h"
#include "GCActivityCallback.h"

#include "HeapInlines.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(VM& vm)
{
    if (!isEnabled())
        return;
    
    ASSERT(vm.currentThreadIsHoldingAPILock());
    Heap& heap = vm.heap;
    if (heap.isDeferred()) {
        scheduleTimer(0_s);
        return;
    }

    doCollection(vm);
}

void GCActivityCallback::scheduleTimer(Seconds newDelay)
{
    if (newDelay * timerSlop > m_delay)
        return;
    Seconds delta = m_delay - newDelay;
    m_delay = newDelay;
    if (auto timeUntilFire = this->timeUntilFire())
        setTimeUntilFire(*timeUntilFire - delta);
    else
        setTimeUntilFire(newDelay);
}

void GCActivityCallback::didAllocate(Heap& heap, 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(heap);
    Seconds newDelay = lastGCLength(heap) / gcTimeSlice(bytesExpectedToReclaim);
    scheduleTimer(newDelay);
}

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

void GCActivityCallback::cancel()
{
    m_delay = s_decade;
    cancelTimer();
}

}