Source/JavaScriptCore/heap/IncrementalSweeper.cpp

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 * Copyright (C) 2012-2023 Apple Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 *    notice, this list of conditions and the following disclaimer in the
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#include "config.h"
#include "IncrementalSweeper.h"

#include "DeferGCInlines.h"
#include "HeapInlines.h"
#include "MarkedBlock.h"
#include "VM.h"
#include <wtf/SystemTracing.h>

#if !USE(SYSTEM_MALLOC)
#include <bmalloc/BPlatform.h>
#if BUSE(LIBPAS)
#include <bmalloc/pas_debug_spectrum.h>
#include <bmalloc/pas_fd_stream.h>
#include <bmalloc/pas_heap_lock.h>
#include <bmalloc/pas_thread_local_cache.h>
#endif
#endif

namespace JSC {

static constexpr Seconds sweepTimeSlice = 10_ms;
static constexpr double sweepTimeTotal = .10;
static constexpr double sweepTimeMultiplier = 1.0 / sweepTimeTotal;

void IncrementalSweeper::scheduleTimer()
{
    setTimeUntilFire(sweepTimeSlice * sweepTimeMultiplier);
}

IncrementalSweeper::IncrementalSweeper(Heap* heap)
    : Base(heap->vm())
    , m_currentDirectory(nullptr)
{
}

void IncrementalSweeper::doWorkUntil(VM& vm, MonotonicTime deadline)
{
    if (!m_currentDirectory)
        m_currentDirectory = vm.heap.objectSpace().firstDirectory();

    if (m_currentDirectory)
        doSweep(vm, deadline, SweepTrigger::OpportunisticTask);
}

void IncrementalSweeper::doWork(VM& vm)
{
    doSweep(vm, MonotonicTime::now() + sweepTimeSlice, SweepTrigger::Timer);
}

void IncrementalSweeper::doSweep(VM& vm, MonotonicTime deadline, SweepTrigger trigger)
{
    std::optional<TraceScope> traceScope;
    if (UNLIKELY(Options::useTracePoints()))
        traceScope.emplace(IncrementalSweepStart, IncrementalSweepEnd, vm.heap.size(), vm.heap.capacity());

    while (sweepNextBlock(vm, trigger)) {
        if (MonotonicTime::now() < deadline)
            continue;

        if (trigger == SweepTrigger::Timer)
            scheduleTimer();
        return;
    }

#if !USE(SYSTEM_MALLOC)
#if BUSE(LIBPAS)
    pas_thread_local_cache_flush_deallocation_log(pas_thread_local_cache_try_get(), pas_lock_is_not_held);
#endif
#endif
    if (m_shouldFreeFastMallocMemoryAfterSweeping) {
        WTF::releaseFastMallocFreeMemory();
        m_shouldFreeFastMallocMemoryAfterSweeping = false;
    }
    cancelTimer();
}

bool IncrementalSweeper::sweepNextBlock(VM& vm, SweepTrigger trigger)
{
    vm.heap.stopIfNecessary();

    MarkedBlock::Handle* block = nullptr;
    
    for (; m_currentDirectory; m_currentDirectory = m_currentDirectory->nextDirectory()) {
        block = m_currentDirectory->findBlockToSweep();
        if (block)
            break;
    }
    
    if (block) {
        DeferGCForAWhile deferGC(vm);
        block->sweep(nullptr);
        if (trigger == SweepTrigger::Timer)
            vm.heap.objectSpace().freeOrShrinkBlock(block);
        return true;
    }

    return vm.heap.sweepNextLogicallyEmptyWeakBlock();
}

void IncrementalSweeper::startSweeping(Heap& heap)
{
    scheduleTimer();
    m_currentDirectory = heap.objectSpace().firstDirectory();
}

void IncrementalSweeper::stopSweeping()
{
    m_currentDirectory = nullptr;
    cancelTimer();
}

} // namespace JSC