Source/JavaScriptCore/heap/MarkedBlock.cpp - WebKit - Git at Google

 /*
  * Copyright (C) 2011-2019 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
  * THE POSSIBILITY OF SUCH DAMAGE.
  */

 #include "config.h"
 #include "MarkedBlock.h"

 #include "AlignedMemoryAllocator.h"
 #include "BlockDirectoryInlines.h"
 #include "FreeListInlines.h"
 #include "JSCast.h"
 #include "JSDestructibleObject.h"
 #include "JSCInlines.h"
 #include "MarkedBlockInlines.h"
 #include "SuperSampler.h"
 #include "SweepingScope.h"
 #include <wtf/CommaPrinter.h>

 namespace JSC {
 namespace MarkedBlockInternal {
 static constexpr bool verbose = false;
 }

 const size_t MarkedBlock::blockSize;

 static constexpr bool computeBalance = false;
 static size_t balance;

 MarkedBlock::Handle* MarkedBlock::tryCreate(Heap& heap, AlignedMemoryAllocator* alignedMemoryAllocator)
 {
     if (computeBalance) {
         balance++;
         if (!(balance % 10))
             dataLog("MarkedBlock Balance: ", balance, "\n");
     }
     void* blockSpace = alignedMemoryAllocator->tryAllocateAlignedMemory(blockSize, blockSize);
     if (!blockSpace)
         return nullptr;
     if (scribbleFreeCells())
         scribble(blockSpace, blockSize);
     return new Handle(heap, alignedMemoryAllocator, blockSpace);
 }

 MarkedBlock::Handle::Handle(Heap& heap, AlignedMemoryAllocator* alignedMemoryAllocator, void* blockSpace)
     : m_alignedMemoryAllocator(alignedMemoryAllocator)
     , m_weakSet(heap.vm(), CellContainer())
 {
     m_block = new (NotNull, blockSpace) MarkedBlock(heap.vm(), *this);

     m_weakSet.setContainer(*m_block);

     heap.didAllocateBlock(blockSize);
 }

 MarkedBlock::Handle::~Handle()
 {
     Heap& heap = *this->heap();
     if (computeBalance) {
         balance--;
         if (!(balance % 10))
             dataLog("MarkedBlock Balance: ", balance, "\n");
     }
     removeFromDirectory();
     m_block->~MarkedBlock();
     m_alignedMemoryAllocator->freeAlignedMemory(m_block);
     heap.didFreeBlock(blockSize);
 }

 MarkedBlock::MarkedBlock(VM& vm, Handle& handle)
 {
     new (&footer()) Footer(vm, handle);
     if (MarkedBlockInternal::verbose)
         dataLog(RawPointer(this), ": Allocated.\n");
 }

 MarkedBlock::~MarkedBlock()
 {
     footer().~Footer();
 }

 MarkedBlock::Footer::Footer(VM& vm, Handle& handle)
     : m_handle(handle)
     , m_vm(&vm)
     , m_markingVersion(MarkedSpace::nullVersion)
     , m_newlyAllocatedVersion(MarkedSpace::nullVersion)
 {
 }

 MarkedBlock::Footer::~Footer()
 {
 }

 void MarkedBlock::Handle::unsweepWithNoNewlyAllocated()
 {
     RELEASE_ASSERT(m_isFreeListed);
     m_isFreeListed = false;
 }

 void MarkedBlock::Handle::setIsFreeListed()
 {
     m_directory->setIsEmpty(NoLockingNecessary, this, false);
     m_isFreeListed = true;
 }

 void MarkedBlock::Handle::stopAllocating(const FreeList& freeList)
 {
     auto locker = holdLock(blockFooter().m_lock);

     if (MarkedBlockInternal::verbose)
         dataLog(RawPointer(this), ": MarkedBlock::Handle::stopAllocating!\n");
     ASSERT(!directory()->isAllocated(NoLockingNecessary, this));

     if (!isFreeListed()) {
         if (MarkedBlockInternal::verbose)
             dataLog("There ain't no newly allocated.\n");
         // This means that we either didn't use this block at all for allocation since last GC,
         // or someone had already done stopAllocating() before.
         ASSERT(freeList.allocationWillFail());
         return;
     }

     if (MarkedBlockInternal::verbose)
         dataLog("Free list: ", freeList, "\n");

     // Roll back to a coherent state for Heap introspection. Cells newly
     // allocated from our free list are not currently marked, so we need another
     // way to tell what's live vs dead.

     blockFooter().m_newlyAllocated.clearAll();
     blockFooter().m_newlyAllocatedVersion = heap()->objectSpace().newlyAllocatedVersion();

     forEachCell(
         [&] (HeapCell* cell, HeapCell::Kind) -> IterationStatus {
             block().setNewlyAllocated(cell);
             return IterationStatus::Continue;
         });

     freeList.forEach(
         [&] (HeapCell* cell) {
             if (MarkedBlockInternal::verbose)
                 dataLog("Free cell: ", RawPointer(cell), "\n");
             if (m_attributes.destruction == NeedsDestruction)
                 cell->zap(HeapCell::StopAllocating);
             block().clearNewlyAllocated(cell);
         });

     m_isFreeListed = false;
 }

 void MarkedBlock::Handle::lastChanceToFinalize()
 {
     directory()->setIsAllocated(NoLockingNecessary, this, false);
     directory()->setIsDestructible(NoLockingNecessary, this, true);
     blockFooter().m_marks.clearAll();
     block().clearHasAnyMarked();
     blockFooter().m_markingVersion = heap()->objectSpace().markingVersion();
     m_weakSet.lastChanceToFinalize();
     blockFooter().m_newlyAllocated.clearAll();
     blockFooter().m_newlyAllocatedVersion = heap()->objectSpace().newlyAllocatedVersion();
     sweep(nullptr);
 }

 void MarkedBlock::Handle::resumeAllocating(FreeList& freeList)
 {
     {
         auto locker = holdLock(blockFooter().m_lock);

         if (MarkedBlockInternal::verbose)
             dataLog(RawPointer(this), ": MarkedBlock::Handle::resumeAllocating!\n");
         ASSERT(!directory()->isAllocated(NoLockingNecessary, this));
         ASSERT(!isFreeListed());

         if (!block().hasAnyNewlyAllocated()) {
             if (MarkedBlockInternal::verbose)
                 dataLog("There ain't no newly allocated.\n");
             // This means we had already exhausted the block when we stopped allocation.
             freeList.clear();
             return;
         }
     }

     // Re-create our free list from before stopping allocation. Note that this may return an empty
     // freelist, in which case the block will still be Marked!
     sweep(&freeList);
 }

 void MarkedBlock::aboutToMarkSlow(HeapVersion markingVersion)
 {
     ASSERT(vm().heap.objectSpace().isMarking());
     auto locker = holdLock(footer().m_lock);

     if (!areMarksStale(markingVersion))
         return;

     BlockDirectory* directory = handle().directory();

     if (handle().directory()->isAllocated(holdLock(directory->bitvectorLock()), &handle())
         || !marksConveyLivenessDuringMarking(markingVersion)) {
         if (MarkedBlockInternal::verbose)
             dataLog(RawPointer(this), ": Clearing marks without doing anything else.\n");
         // We already know that the block is full and is already recognized as such, or that the
         // block did not survive the previous GC. So, we can clear mark bits the old fashioned
         // way. Note that it's possible for such a block to have newlyAllocated with an up-to-
         // date version! If it does, then we want to leave the newlyAllocated alone, since that
         // means that we had allocated in this previously empty block but did not fill it up, so
         // we created a newlyAllocated.
         footer().m_marks.clearAll();
     } else {
         if (MarkedBlockInternal::verbose)
             dataLog(RawPointer(this), ": Doing things.\n");
         HeapVersion newlyAllocatedVersion = space()->newlyAllocatedVersion();
         if (footer().m_newlyAllocatedVersion == newlyAllocatedVersion) {
             // When do we get here? The block could not have been filled up. The newlyAllocated bits would
             // have had to be created since the end of the last collection. The only things that create
             // them are aboutToMarkSlow, lastChanceToFinalize, and stopAllocating. If it had been
             // aboutToMarkSlow, then we shouldn't be here since the marks wouldn't be stale anymore. It
             // cannot be lastChanceToFinalize. So it must be stopAllocating. That means that we just
             // computed the newlyAllocated bits just before the start of an increment. When we are in that
             // mode, it seems as if newlyAllocated should subsume marks.
             ASSERT(footer().m_newlyAllocated.subsumes(footer().m_marks));
             footer().m_marks.clearAll();
         } else {
             footer().m_newlyAllocated.setAndClear(footer().m_marks);
             footer().m_newlyAllocatedVersion = newlyAllocatedVersion;
         }
     }
     clearHasAnyMarked();
     WTF::storeStoreFence();
     footer().m_markingVersion = markingVersion;

     // This means we're the first ones to mark any object in this block.
     directory->setIsMarkingNotEmpty(holdLock(directory->bitvectorLock()), &handle(), true);
 }

 void MarkedBlock::resetAllocated()
 {
     footer().m_newlyAllocated.clearAll();
     footer().m_newlyAllocatedVersion = MarkedSpace::nullVersion;
 }

 void MarkedBlock::resetMarks()
 {
     // We want aboutToMarkSlow() to see what the mark bits were after the last collection. It uses
     // the version number to distinguish between the marks having already been stale before
     // beginMarking(), or just stale now that beginMarking() bumped the version. If we have a version
     // wraparound, then we will call this method before resetting the version to null. When the
     // version is null, aboutToMarkSlow() will assume that the marks were not stale as of before
     // beginMarking(). Hence the need to whip the marks into shape.
     if (areMarksStale())
         footer().m_marks.clearAll();
     footer().m_markingVersion = MarkedSpace::nullVersion;
 }

 #if !ASSERT_DISABLED
 void MarkedBlock::assertMarksNotStale()
 {
     ASSERT(footer().m_markingVersion == vm().heap.objectSpace().markingVersion());
 }
 #endif // !ASSERT_DISABLED

 bool MarkedBlock::areMarksStale()
 {
     return areMarksStale(vm().heap.objectSpace().markingVersion());
 }

 bool MarkedBlock::Handle::areMarksStale()
 {
     return m_block->areMarksStale();
 }

 bool MarkedBlock::isMarked(const void* p)
 {
     return isMarked(vm().heap.objectSpace().markingVersion(), p);
 }

 void MarkedBlock::Handle::didConsumeFreeList()
 {
     auto locker = holdLock(blockFooter().m_lock);
     if (MarkedBlockInternal::verbose)
         dataLog(RawPointer(this), ": MarkedBlock::Handle::didConsumeFreeList!\n");
     ASSERT(isFreeListed());
     m_isFreeListed = false;
     directory()->setIsAllocated(NoLockingNecessary, this, true);
 }

 size_t MarkedBlock::markCount()
 {
     return areMarksStale() ? 0 : footer().m_marks.count();
 }

 void MarkedBlock::clearHasAnyMarked()
 {
     footer().m_biasedMarkCount = footer().m_markCountBias;
 }

 void MarkedBlock::noteMarkedSlow()
 {
     BlockDirectory* directory = handle().directory();
     directory->setIsMarkingRetired(holdLock(directory->bitvectorLock()), &handle(), true);
 }

 void MarkedBlock::Handle::removeFromDirectory()
 {
     if (!m_directory)
         return;

     m_directory->removeBlock(this);
 }

 void MarkedBlock::Handle::didAddToDirectory(BlockDirectory* directory, size_t index)
 {
     ASSERT(m_index == std::numeric_limits<size_t>::max());
     ASSERT(!m_directory);

     RELEASE_ASSERT(directory->subspace()->alignedMemoryAllocator() == m_alignedMemoryAllocator);

     m_index = index;
     m_directory = directory;
     blockFooter().m_subspace = directory->subspace();

     size_t cellSize = directory->cellSize();
     m_atomsPerCell = (cellSize + atomSize - 1) / atomSize;
     m_endAtom = endAtom - m_atomsPerCell + 1;

     m_attributes = directory->attributes();

     if (!isJSCellKind(m_attributes.cellKind))
         RELEASE_ASSERT(m_attributes.destruction == DoesNotNeedDestruction);

     double markCountBias = -(Options::minMarkedBlockUtilization() * cellsPerBlock());

     // The mark count bias should be comfortably within this range.
     RELEASE_ASSERT(markCountBias > static_cast<double>(std::numeric_limits<int16_t>::min()));
     RELEASE_ASSERT(markCountBias < 0);

     // This means we haven't marked anything yet.
     blockFooter().m_biasedMarkCount = blockFooter().m_markCountBias = static_cast<int16_t>(markCountBias);
 }

 void MarkedBlock::Handle::didRemoveFromDirectory()
 {
     ASSERT(m_index != std::numeric_limits<size_t>::max());
     ASSERT(m_directory);

     m_index = std::numeric_limits<size_t>::max();
     m_directory = nullptr;
     blockFooter().m_subspace = nullptr;
 }

 #if !ASSERT_DISABLED
 void MarkedBlock::assertValidCell(VM& vm, HeapCell* cell) const
 {
     RELEASE_ASSERT(&vm == &this->vm());
     RELEASE_ASSERT(const_cast<MarkedBlock*>(this)->handle().cellAlign(cell) == cell);
 }
 #endif

 void MarkedBlock::Handle::dumpState(PrintStream& out)
 {
     CommaPrinter comma;
     directory()->forEachBitVectorWithName(
         holdLock(directory()->bitvectorLock()),
         [&] (FastBitVector& bitvector, const char* name) {
             out.print(comma, name, ":", bitvector[index()] ? "YES" : "no");
         });
 }

 Subspace* MarkedBlock::Handle::subspace() const
 {
     return directory()->subspace();
 }

 void MarkedBlock::Handle::sweep(FreeList* freeList)
 {
     SweepingScope sweepingScope(*heap());

     SweepMode sweepMode = freeList ? SweepToFreeList : SweepOnly;

     m_directory->setIsUnswept(NoLockingNecessary, this, false);

     m_weakSet.sweep();

     bool needsDestruction = m_attributes.destruction == NeedsDestruction
         && m_directory->isDestructible(NoLockingNecessary, this);

     if (sweepMode == SweepOnly && !needsDestruction)
         return;

     if (m_isFreeListed) {
         dataLog("FATAL: ", RawPointer(this), "->sweep: block is free-listed.\n");
         RELEASE_ASSERT_NOT_REACHED();
     }

     if (isAllocated()) {
         dataLog("FATAL: ", RawPointer(this), "->sweep: block is allocated.\n");
         RELEASE_ASSERT_NOT_REACHED();
     }

     if (space()->isMarking())
         blockFooter().m_lock.lock();

     subspace()->didBeginSweepingToFreeList(this);

     if (needsDestruction) {
         subspace()->finishSweep(*this, freeList);
         return;
     }

     // Handle the no-destructor specializations here, since we have the most of those. This
     // ensures that they don't get re-specialized for every destructor space.

     EmptyMode emptyMode = this->emptyMode();
     ScribbleMode scribbleMode = this->scribbleMode();
     NewlyAllocatedMode newlyAllocatedMode = this->newlyAllocatedMode();
     MarksMode marksMode = this->marksMode();

     auto trySpecialized = [&] () -> bool {
         if (sweepMode != SweepToFreeList)
             return false;
         if (scribbleMode != DontScribble)
             return false;
         if (newlyAllocatedMode != DoesNotHaveNewlyAllocated)
             return false;

         switch (emptyMode) {
         case IsEmpty:
             switch (marksMode) {
             case MarksNotStale:
                 specializedSweep<true, IsEmpty, SweepToFreeList, BlockHasNoDestructors, DontScribble, DoesNotHaveNewlyAllocated, MarksNotStale>(freeList, IsEmpty, SweepToFreeList, BlockHasNoDestructors, DontScribble, DoesNotHaveNewlyAllocated, MarksNotStale, [] (VM&, JSCell*) { });
                 return true;
             case MarksStale:
                 specializedSweep<true, IsEmpty, SweepToFreeList, BlockHasNoDestructors, DontScribble, DoesNotHaveNewlyAllocated, MarksStale>(freeList, IsEmpty, SweepToFreeList, BlockHasNoDestructors, DontScribble, DoesNotHaveNewlyAllocated, MarksStale, [] (VM&, JSCell*) { });
                 return true;
             }
             break;
         case NotEmpty:
             switch (marksMode) {
             case MarksNotStale:
                 specializedSweep<true, NotEmpty, SweepToFreeList, BlockHasNoDestructors, DontScribble, DoesNotHaveNewlyAllocated, MarksNotStale>(freeList, IsEmpty, SweepToFreeList, BlockHasNoDestructors, DontScribble, DoesNotHaveNewlyAllocated, MarksNotStale, [] (VM&, JSCell*) { });
                 return true;
             case MarksStale:
                 specializedSweep<true, NotEmpty, SweepToFreeList, BlockHasNoDestructors, DontScribble, DoesNotHaveNewlyAllocated, MarksStale>(freeList, IsEmpty, SweepToFreeList, BlockHasNoDestructors, DontScribble, DoesNotHaveNewlyAllocated, MarksStale, [] (VM&, JSCell*) { });
                 return true;
             }
             break;
         }

         return false;
     };

     if (trySpecialized())
         return;

     // The template arguments don't matter because the first one is false.
     specializedSweep<false, IsEmpty, SweepOnly, BlockHasNoDestructors, DontScribble, HasNewlyAllocated, MarksStale>(freeList, emptyMode, sweepMode, BlockHasNoDestructors, scribbleMode, newlyAllocatedMode, marksMode, [] (VM&, JSCell*) { });
 }

 bool MarkedBlock::Handle::isFreeListedCell(const void* target) const
 {
     ASSERT(isFreeListed());
     return m_directory->isFreeListedCell(target);
 }

 } // namespace JSC

 namespace WTF {

 void printInternal(PrintStream& out, JSC::MarkedBlock::Handle::SweepMode mode)
 {
     switch (mode) {
     case JSC::MarkedBlock::Handle::SweepToFreeList:
         out.print("SweepToFreeList");
         return;
     case JSC::MarkedBlock::Handle::SweepOnly:
         out.print("SweepOnly");
         return;
     }
     RELEASE_ASSERT_NOT_REACHED();
 }

 } // namespace WTF
	/*
	* Copyright (C) 2011-2019 Apple Inc. All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	*
	* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
	* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
	* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
	* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
	* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
	* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
	* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
	* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
	* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
	* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
	* THE POSSIBILITY OF SUCH DAMAGE.
	*/

	#include "config.h"
	#include "MarkedBlock.h"

	#include "AlignedMemoryAllocator.h"
	#include "BlockDirectoryInlines.h"
	#include "FreeListInlines.h"
	#include "JSCast.h"
	#include "JSDestructibleObject.h"
	#include "JSCInlines.h"
	#include "MarkedBlockInlines.h"
	#include "SuperSampler.h"
	#include "SweepingScope.h"
	#include <wtf/CommaPrinter.h>

	namespace JSC {
	namespace MarkedBlockInternal {
	static constexpr bool verbose = false;
	}

	const size_t MarkedBlock::blockSize;

	static constexpr bool computeBalance = false;
	static size_t balance;

	MarkedBlock::Handle* MarkedBlock::tryCreate(Heap& heap, AlignedMemoryAllocator* alignedMemoryAllocator)
	{
	if (computeBalance) {
	balance++;
	if (!(balance % 10))
	dataLog("MarkedBlock Balance: ", balance, "\n");
	}
	void* blockSpace = alignedMemoryAllocator->tryAllocateAlignedMemory(blockSize, blockSize);
	if (!blockSpace)
	return nullptr;
	if (scribbleFreeCells())
	scribble(blockSpace, blockSize);
	return new Handle(heap, alignedMemoryAllocator, blockSpace);
	}

	MarkedBlock::Handle::Handle(Heap& heap, AlignedMemoryAllocator* alignedMemoryAllocator, void* blockSpace)
	: m_alignedMemoryAllocator(alignedMemoryAllocator)
	, m_weakSet(heap.vm(), CellContainer())
	{
	m_block = new (NotNull, blockSpace) MarkedBlock(heap.vm(), *this);

	m_weakSet.setContainer(*m_block);

	heap.didAllocateBlock(blockSize);
	}

	MarkedBlock::Handle::~Handle()
	{
	Heap& heap = *this->heap();
	if (computeBalance) {
	balance--;
	if (!(balance % 10))
	dataLog("MarkedBlock Balance: ", balance, "\n");
	}
	removeFromDirectory();
	m_block->~MarkedBlock();
	m_alignedMemoryAllocator->freeAlignedMemory(m_block);
	heap.didFreeBlock(blockSize);
	}

	MarkedBlock::MarkedBlock(VM& vm, Handle& handle)
	{
	new (&footer()) Footer(vm, handle);
	if (MarkedBlockInternal::verbose)
	dataLog(RawPointer(this), ": Allocated.\n");
	}

	MarkedBlock::~MarkedBlock()
	{
	footer().~Footer();
	}

	MarkedBlock::Footer::Footer(VM& vm, Handle& handle)
	: m_handle(handle)
	, m_vm(&vm)
	, m_markingVersion(MarkedSpace::nullVersion)
	, m_newlyAllocatedVersion(MarkedSpace::nullVersion)
	{
	}

	MarkedBlock::Footer::~Footer()
	{
	}

	void MarkedBlock::Handle::unsweepWithNoNewlyAllocated()
	{
	RELEASE_ASSERT(m_isFreeListed);
	m_isFreeListed = false;
	}

	void MarkedBlock::Handle::setIsFreeListed()
	{
	m_directory->setIsEmpty(NoLockingNecessary, this, false);
	m_isFreeListed = true;
	}

	void MarkedBlock::Handle::stopAllocating(const FreeList& freeList)
	{
	auto locker = holdLock(blockFooter().m_lock);

	if (MarkedBlockInternal::verbose)
	dataLog(RawPointer(this), ": MarkedBlock::Handle::stopAllocating!\n");
	ASSERT(!directory()->isAllocated(NoLockingNecessary, this));

	if (!isFreeListed()) {
	if (MarkedBlockInternal::verbose)
	dataLog("There ain't no newly allocated.\n");
	// This means that we either didn't use this block at all for allocation since last GC,
	// or someone had already done stopAllocating() before.
	ASSERT(freeList.allocationWillFail());
	return;
	}

	if (MarkedBlockInternal::verbose)
	dataLog("Free list: ", freeList, "\n");

	// Roll back to a coherent state for Heap introspection. Cells newly
	// allocated from our free list are not currently marked, so we need another
	// way to tell what's live vs dead.

	blockFooter().m_newlyAllocated.clearAll();
	blockFooter().m_newlyAllocatedVersion = heap()->objectSpace().newlyAllocatedVersion();

	forEachCell(
	[&] (HeapCell* cell, HeapCell::Kind) -> IterationStatus {
	block().setNewlyAllocated(cell);
	return IterationStatus::Continue;
	});

	freeList.forEach(
	[&] (HeapCell* cell) {
	if (MarkedBlockInternal::verbose)
	dataLog("Free cell: ", RawPointer(cell), "\n");
	if (m_attributes.destruction == NeedsDestruction)
	cell->zap(HeapCell::StopAllocating);
	block().clearNewlyAllocated(cell);
	});

	m_isFreeListed = false;
	}

	void MarkedBlock::Handle::lastChanceToFinalize()
	{
	directory()->setIsAllocated(NoLockingNecessary, this, false);
	directory()->setIsDestructible(NoLockingNecessary, this, true);
	blockFooter().m_marks.clearAll();
	block().clearHasAnyMarked();
	blockFooter().m_markingVersion = heap()->objectSpace().markingVersion();
	m_weakSet.lastChanceToFinalize();
	blockFooter().m_newlyAllocated.clearAll();
	blockFooter().m_newlyAllocatedVersion = heap()->objectSpace().newlyAllocatedVersion();
	sweep(nullptr);
	}

	void MarkedBlock::Handle::resumeAllocating(FreeList& freeList)
	{
	{
	auto locker = holdLock(blockFooter().m_lock);

	if (MarkedBlockInternal::verbose)
	dataLog(RawPointer(this), ": MarkedBlock::Handle::resumeAllocating!\n");
	ASSERT(!directory()->isAllocated(NoLockingNecessary, this));
	ASSERT(!isFreeListed());

	if (!block().hasAnyNewlyAllocated()) {
	if (MarkedBlockInternal::verbose)
	dataLog("There ain't no newly allocated.\n");
	// This means we had already exhausted the block when we stopped allocation.
	freeList.clear();
	return;
	}
	}

	// Re-create our free list from before stopping allocation. Note that this may return an empty
	// freelist, in which case the block will still be Marked!
	sweep(&freeList);
	}

	void MarkedBlock::aboutToMarkSlow(HeapVersion markingVersion)
	{
	ASSERT(vm().heap.objectSpace().isMarking());
	auto locker = holdLock(footer().m_lock);

	if (!areMarksStale(markingVersion))
	return;

	BlockDirectory* directory = handle().directory();

	if (handle().directory()->isAllocated(holdLock(directory->bitvectorLock()), &handle())
	\|\| !marksConveyLivenessDuringMarking(markingVersion)) {
	if (MarkedBlockInternal::verbose)
	dataLog(RawPointer(this), ": Clearing marks without doing anything else.\n");
	// We already know that the block is full and is already recognized as such, or that the
	// block did not survive the previous GC. So, we can clear mark bits the old fashioned
	// way. Note that it's possible for such a block to have newlyAllocated with an up-to-
	// date version! If it does, then we want to leave the newlyAllocated alone, since that
	// means that we had allocated in this previously empty block but did not fill it up, so
	// we created a newlyAllocated.
	footer().m_marks.clearAll();
	} else {
	if (MarkedBlockInternal::verbose)
	dataLog(RawPointer(this), ": Doing things.\n");
	HeapVersion newlyAllocatedVersion = space()->newlyAllocatedVersion();
	if (footer().m_newlyAllocatedVersion == newlyAllocatedVersion) {
	// When do we get here? The block could not have been filled up. The newlyAllocated bits would
	// have had to be created since the end of the last collection. The only things that create
	// them are aboutToMarkSlow, lastChanceToFinalize, and stopAllocating. If it had been
	// aboutToMarkSlow, then we shouldn't be here since the marks wouldn't be stale anymore. It
	// cannot be lastChanceToFinalize. So it must be stopAllocating. That means that we just
	// computed the newlyAllocated bits just before the start of an increment. When we are in that
	// mode, it seems as if newlyAllocated should subsume marks.
	ASSERT(footer().m_newlyAllocated.subsumes(footer().m_marks));
	footer().m_marks.clearAll();
	} else {
	footer().m_newlyAllocated.setAndClear(footer().m_marks);
	footer().m_newlyAllocatedVersion = newlyAllocatedVersion;
	}
	}
	clearHasAnyMarked();
	WTF::storeStoreFence();
	footer().m_markingVersion = markingVersion;

	// This means we're the first ones to mark any object in this block.
	directory->setIsMarkingNotEmpty(holdLock(directory->bitvectorLock()), &handle(), true);
	}

	void MarkedBlock::resetAllocated()
	{
	footer().m_newlyAllocated.clearAll();
	footer().m_newlyAllocatedVersion = MarkedSpace::nullVersion;
	}

	void MarkedBlock::resetMarks()
	{
	// We want aboutToMarkSlow() to see what the mark bits were after the last collection. It uses
	// the version number to distinguish between the marks having already been stale before
	// beginMarking(), or just stale now that beginMarking() bumped the version. If we have a version
	// wraparound, then we will call this method before resetting the version to null. When the
	// version is null, aboutToMarkSlow() will assume that the marks were not stale as of before
	// beginMarking(). Hence the need to whip the marks into shape.
	if (areMarksStale())
	footer().m_marks.clearAll();
	footer().m_markingVersion = MarkedSpace::nullVersion;
	}

	#if !ASSERT_DISABLED
	void MarkedBlock::assertMarksNotStale()
	{
	ASSERT(footer().m_markingVersion == vm().heap.objectSpace().markingVersion());
	}
	#endif // !ASSERT_DISABLED

	bool MarkedBlock::areMarksStale()
	{
	return areMarksStale(vm().heap.objectSpace().markingVersion());
	}

	bool MarkedBlock::Handle::areMarksStale()
	{
	return m_block->areMarksStale();
	}

	bool MarkedBlock::isMarked(const void* p)
	{
	return isMarked(vm().heap.objectSpace().markingVersion(), p);
	}

	void MarkedBlock::Handle::didConsumeFreeList()
	{
	auto locker = holdLock(blockFooter().m_lock);
	if (MarkedBlockInternal::verbose)
	dataLog(RawPointer(this), ": MarkedBlock::Handle::didConsumeFreeList!\n");
	ASSERT(isFreeListed());
	m_isFreeListed = false;
	directory()->setIsAllocated(NoLockingNecessary, this, true);
	}

	size_t MarkedBlock::markCount()
	{
	return areMarksStale() ? 0 : footer().m_marks.count();
	}

	void MarkedBlock::clearHasAnyMarked()
	{
	footer().m_biasedMarkCount = footer().m_markCountBias;
	}

	void MarkedBlock::noteMarkedSlow()
	{
	BlockDirectory* directory = handle().directory();
	directory->setIsMarkingRetired(holdLock(directory->bitvectorLock()), &handle(), true);
	}

	void MarkedBlock::Handle::removeFromDirectory()
	{
	if (!m_directory)
	return;

	m_directory->removeBlock(this);
	}

	void MarkedBlock::Handle::didAddToDirectory(BlockDirectory* directory, size_t index)
	{
	ASSERT(m_index == std::numeric_limits<size_t>::max());
	ASSERT(!m_directory);

	RELEASE_ASSERT(directory->subspace()->alignedMemoryAllocator() == m_alignedMemoryAllocator);

	m_index = index;
	m_directory = directory;
	blockFooter().m_subspace = directory->subspace();

	size_t cellSize = directory->cellSize();
	m_atomsPerCell = (cellSize + atomSize - 1) / atomSize;
	m_endAtom = endAtom - m_atomsPerCell + 1;

	m_attributes = directory->attributes();

	if (!isJSCellKind(m_attributes.cellKind))
	RELEASE_ASSERT(m_attributes.destruction == DoesNotNeedDestruction);

	double markCountBias = -(Options::minMarkedBlockUtilization() * cellsPerBlock());

	// The mark count bias should be comfortably within this range.
	RELEASE_ASSERT(markCountBias > static_cast<double>(std::numeric_limits<int16_t>::min()));
	RELEASE_ASSERT(markCountBias < 0);

	// This means we haven't marked anything yet.
	blockFooter().m_biasedMarkCount = blockFooter().m_markCountBias = static_cast<int16_t>(markCountBias);
	}

	void MarkedBlock::Handle::didRemoveFromDirectory()
	{
	ASSERT(m_index != std::numeric_limits<size_t>::max());
	ASSERT(m_directory);

	m_index = std::numeric_limits<size_t>::max();
	m_directory = nullptr;
	blockFooter().m_subspace = nullptr;
	}

	#if !ASSERT_DISABLED
	void MarkedBlock::assertValidCell(VM& vm, HeapCell* cell) const
	{
	RELEASE_ASSERT(&vm == &this->vm());
	RELEASE_ASSERT(const_cast<MarkedBlock*>(this)->handle().cellAlign(cell) == cell);
	}
	#endif

	void MarkedBlock::Handle::dumpState(PrintStream& out)
	{
	CommaPrinter comma;
	directory()->forEachBitVectorWithName(
	holdLock(directory()->bitvectorLock()),
	[&] (FastBitVector& bitvector, const char* name) {
	out.print(comma, name, ":", bitvector[index()] ? "YES" : "no");
	});
	}

	Subspace* MarkedBlock::Handle::subspace() const
	{
	return directory()->subspace();
	}

	void MarkedBlock::Handle::sweep(FreeList* freeList)
	{
	SweepingScope sweepingScope(*heap());

	SweepMode sweepMode = freeList ? SweepToFreeList : SweepOnly;

	m_directory->setIsUnswept(NoLockingNecessary, this, false);

	m_weakSet.sweep();

	bool needsDestruction = m_attributes.destruction == NeedsDestruction
	&& m_directory->isDestructible(NoLockingNecessary, this);

	if (sweepMode == SweepOnly && !needsDestruction)
	return;

	if (m_isFreeListed) {
	dataLog("FATAL: ", RawPointer(this), "->sweep: block is free-listed.\n");
	RELEASE_ASSERT_NOT_REACHED();
	}

	if (isAllocated()) {
	dataLog("FATAL: ", RawPointer(this), "->sweep: block is allocated.\n");
	RELEASE_ASSERT_NOT_REACHED();
	}

	if (space()->isMarking())
	blockFooter().m_lock.lock();

	subspace()->didBeginSweepingToFreeList(this);

	if (needsDestruction) {
	subspace()->finishSweep(*this, freeList);
	return;
	}

	// Handle the no-destructor specializations here, since we have the most of those. This
	// ensures that they don't get re-specialized for every destructor space.

	EmptyMode emptyMode = this->emptyMode();
	ScribbleMode scribbleMode = this->scribbleMode();
	NewlyAllocatedMode newlyAllocatedMode = this->newlyAllocatedMode();
	MarksMode marksMode = this->marksMode();

	auto trySpecialized = [&] () -> bool {
	if (sweepMode != SweepToFreeList)
	return false;
	if (scribbleMode != DontScribble)
	return false;
	if (newlyAllocatedMode != DoesNotHaveNewlyAllocated)
	return false;

	switch (emptyMode) {
	case IsEmpty:
	switch (marksMode) {
	case MarksNotStale:
	specializedSweep<true, IsEmpty, SweepToFreeList, BlockHasNoDestructors, DontScribble, DoesNotHaveNewlyAllocated, MarksNotStale>(freeList, IsEmpty, SweepToFreeList, BlockHasNoDestructors, DontScribble, DoesNotHaveNewlyAllocated, MarksNotStale, [] (VM&, JSCell*) { });
	return true;
	case MarksStale:
	specializedSweep<true, IsEmpty, SweepToFreeList, BlockHasNoDestructors, DontScribble, DoesNotHaveNewlyAllocated, MarksStale>(freeList, IsEmpty, SweepToFreeList, BlockHasNoDestructors, DontScribble, DoesNotHaveNewlyAllocated, MarksStale, [] (VM&, JSCell*) { });
	return true;
	}
	break;
	case NotEmpty:
	switch (marksMode) {
	case MarksNotStale:
	specializedSweep<true, NotEmpty, SweepToFreeList, BlockHasNoDestructors, DontScribble, DoesNotHaveNewlyAllocated, MarksNotStale>(freeList, IsEmpty, SweepToFreeList, BlockHasNoDestructors, DontScribble, DoesNotHaveNewlyAllocated, MarksNotStale, [] (VM&, JSCell*) { });
	return true;
	case MarksStale:
	specializedSweep<true, NotEmpty, SweepToFreeList, BlockHasNoDestructors, DontScribble, DoesNotHaveNewlyAllocated, MarksStale>(freeList, IsEmpty, SweepToFreeList, BlockHasNoDestructors, DontScribble, DoesNotHaveNewlyAllocated, MarksStale, [] (VM&, JSCell*) { });
	return true;
	}
	break;
	}

	return false;
	};

	if (trySpecialized())
	return;

	// The template arguments don't matter because the first one is false.
	specializedSweep<false, IsEmpty, SweepOnly, BlockHasNoDestructors, DontScribble, HasNewlyAllocated, MarksStale>(freeList, emptyMode, sweepMode, BlockHasNoDestructors, scribbleMode, newlyAllocatedMode, marksMode, [] (VM&, JSCell*) { });
	}

	bool MarkedBlock::Handle::isFreeListedCell(const void* target) const
	{
	ASSERT(isFreeListed());
	return m_directory->isFreeListedCell(target);
	}

	} // namespace JSC

	namespace WTF {

	void printInternal(PrintStream& out, JSC::MarkedBlock::Handle::SweepMode mode)
	{
	switch (mode) {
	case JSC::MarkedBlock::Handle::SweepToFreeList:
	out.print("SweepToFreeList");
	return;
	case JSC::MarkedBlock::Handle::SweepOnly:
	out.print("SweepOnly");
	return;
	}
	RELEASE_ASSERT_NOT_REACHED();
	}

	} // namespace WTF