Source/JavaScriptCore/heap/WeakBlock.cpp

/*
 * Copyright (C) 2012-2017 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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 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
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#include "config.h"
#include "WeakBlock.h"

#include "CellContainerInlines.h"
#include "Heap.h"
#include "HeapSnapshotBuilder.h"
#include "JSCInlines.h"
#include "JSObject.h"
#include "WeakHandleOwner.h"

namespace JSC {

WeakBlock* WeakBlock::create(Heap& heap, CellContainer container)
{
    heap.didAllocateBlock(WeakBlock::blockSize);
    return new (NotNull, fastMalloc(blockSize)) WeakBlock(container);
}

void WeakBlock::destroy(Heap& heap, WeakBlock* block)
{
    block->~WeakBlock();
    fastFree(block);
    heap.didFreeBlock(WeakBlock::blockSize);
}

WeakBlock::WeakBlock(CellContainer container)
    : DoublyLinkedListNode<WeakBlock>()
    , m_container(container)
{
    for (size_t i = 0; i < weakImplCount(); ++i) {
        WeakImpl* weakImpl = &weakImpls()[i];
        new (NotNull, weakImpl) WeakImpl;
        addToFreeList(&m_sweepResult.freeList, weakImpl);
    }

    ASSERT(isEmpty());
}

void WeakBlock::lastChanceToFinalize()
{
    for (size_t i = 0; i < weakImplCount(); ++i) {
        WeakImpl* weakImpl = &weakImpls()[i];
        if (weakImpl->state() >= WeakImpl::Finalized)
            continue;
        weakImpl->setState(WeakImpl::Dead);
        finalize(weakImpl);
    }
}

void WeakBlock::sweep()
{
    // If a block is completely empty, a sweep won't have any effect.
    if (isEmpty())
        return;

    SweepResult sweepResult;
    for (size_t i = 0; i < weakImplCount(); ++i) {
        WeakImpl* weakImpl = &weakImpls()[i];
        if (weakImpl->state() == WeakImpl::Dead)
            finalize(weakImpl);
        if (weakImpl->state() == WeakImpl::Deallocated)
            addToFreeList(&sweepResult.freeList, weakImpl);
        else {
            sweepResult.blockIsFree = false;
            if (weakImpl->state() == WeakImpl::Live)
                sweepResult.blockIsLogicallyEmpty = false;
        }
    }

    m_sweepResult = sweepResult;
    ASSERT(!m_sweepResult.isNull());
}

template<typename ContainerType>
void WeakBlock::specializedVisit(ContainerType& container, SlotVisitor& visitor)
{
    HeapVersion markingVersion = visitor.markingVersion();

    size_t count = weakImplCount();
    for (size_t i = 0; i < count; ++i) {
        WeakImpl* weakImpl = &weakImpls()[i];
        if (weakImpl->state() != WeakImpl::Live)
            continue;

        WeakHandleOwner* weakHandleOwner = weakImpl->weakHandleOwner();
        if (!weakHandleOwner)
            continue;

        JSValue jsValue = weakImpl->jsValue();
        if (container.isMarked(markingVersion, jsValue.asCell()))
            continue;
        
        const char* reason = "";
        const char** reasonPtr = nullptr;
        if (UNLIKELY(visitor.isBuildingHeapSnapshot()))
            reasonPtr = &reason;

        if (!weakHandleOwner->isReachableFromOpaqueRoots(Handle<Unknown>::wrapSlot(&const_cast<JSValue&>(jsValue)), weakImpl->context(), visitor, reasonPtr))
            continue;

        visitor.appendUnbarriered(jsValue);

        if (UNLIKELY(visitor.isBuildingHeapSnapshot())) {
            if (jsValue.isCell())
                visitor.heapSnapshotBuilder()->setOpaqueRootReachabilityReasonForCell(jsValue.asCell(), *reasonPtr);
        }
    }
}

void WeakBlock::visit(SlotVisitor& visitor)
{
    // If a block is completely empty, a visit won't have any effect.
    if (isEmpty())
        return;

    // If this WeakBlock doesn't belong to a CellContainer, we won't even be here.
    ASSERT(m_container);
    
    if (m_container.isLargeAllocation())
        specializedVisit(m_container.largeAllocation(), visitor);
    else
        specializedVisit(m_container.markedBlock(), visitor);
}

void WeakBlock::reap()
{
    // If a block is completely empty, a reaping won't have any effect.
    if (isEmpty())
        return;

    // If this WeakBlock doesn't belong to a CellContainer, we won't even be here.
    ASSERT(m_container);
    
    HeapVersion markingVersion = m_container.heap()->objectSpace().markingVersion();

    for (size_t i = 0; i < weakImplCount(); ++i) {
        WeakImpl* weakImpl = &weakImpls()[i];
        if (weakImpl->state() > WeakImpl::Dead)
            continue;

        if (m_container.isMarked(markingVersion, weakImpl->jsValue().asCell())) {
            ASSERT(weakImpl->state() == WeakImpl::Live);
            continue;
        }

        weakImpl->setState(WeakImpl::Dead);
    }
}

} // namespace JSC