src/gc/mod_union_table.cc - platform/art - Git at Google

 /*
  * Copyright (C) 2012 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include "heap.h"
 #include "heap_bitmap.h"
 #include "mark_sweep.h"
 #include "mod_union_table.h"
 #include "space.h"
 #include "stl_util.h"
 #include "UniquePtr.h"

 namespace art {

 class MarkIfReachesAllocspaceVisitor {
  public:
   explicit MarkIfReachesAllocspaceVisitor(Heap* const heap, SpaceBitmap* bitmap)
     : heap_(heap),
       bitmap_(bitmap) {
   }

   // Extra parameters are required since we use this same visitor signature for checking objects.
   void operator ()(const Object* obj, const Object* ref, const MemberOffset& /* offset */, bool /* is_static */) const {
     // TODO: Optimize?
     // TODO: C++0x auto
     const Spaces& spaces = heap_->GetSpaces();
     for (Spaces::const_iterator cur = spaces.begin(); cur != spaces.end(); ++cur) {
       if ((*cur)->IsAllocSpace() && (*cur)->Contains(ref)) {
         bitmap_->Set(obj);
         break;
       }
     }
   }

  private:
   Heap* const heap_;
   SpaceBitmap* bitmap_;
 };

 class ModUnionVisitor {
  public:
   explicit ModUnionVisitor(Heap* const heap, SpaceBitmap* bitmap)
     : heap_(heap),
       bitmap_(bitmap) {
   }

   void operator ()(const Object* obj) const
       SHARED_LOCKS_REQUIRED(Locks::heap_bitmap_lock_,
                             Locks::mutator_lock_) {
     DCHECK(obj != NULL);
     // We don't have an early exit since we use the visitor pattern, an early exit should
     // significantly speed this up.
     MarkIfReachesAllocspaceVisitor visitor(heap_, bitmap_);
     MarkSweep::VisitObjectReferences(obj, visitor);
   }
  private:
   Heap* const heap_;
   SpaceBitmap* bitmap_;
 };

 class ModUnionClearCardSetVisitor {
  public:
   explicit ModUnionClearCardSetVisitor(std::set<byte*>* const cleared_cards)
     : cleared_cards_(cleared_cards) {
   }

   inline void operator ()(byte* card, byte expected_value, byte new_value) const {
     if (expected_value == CardTable::kCardDirty) {
       cleared_cards_->insert(card);
     }
   }

  private:
   std::set<byte*>* const cleared_cards_;
 };

 class ModUnionClearCardVisitor {
  public:
   explicit ModUnionClearCardVisitor(std::vector<byte*>* cleared_cards)
     : cleared_cards_(cleared_cards) {
   }

   void operator ()(byte* card, byte expected_card, byte new_card) const {
     if (expected_card == CardTable::kCardDirty) {
       cleared_cards_->push_back(card);
     }
   }
  private:
   std::vector<byte*>* cleared_cards_;
 };

 ModUnionTableBitmap::ModUnionTableBitmap(Heap* heap) : ModUnionTable(heap)  {
   // Prevent fragmentation of the heap which is caused by resizing of the vector.
   // TODO: Make a new vector which uses madvise (basically same as a mark stack).
   cleared_cards_.reserve(32);
   const Spaces& spaces = heap->GetSpaces();
   // Create one heap bitmap per image space.
   // TODO: C++0x auto
   for (Spaces::const_iterator it = spaces.begin(); it != spaces.end(); ++it) {
     ContinuousSpace* space = *it;
     if (space->IsImageSpace()) {
       // The mod-union table is only needed when we have an image space since it's purpose is to
       // cache image roots.
       UniquePtr<SpaceBitmap> bitmap(SpaceBitmap::Create("mod-union table bitmap", space->Begin(),
                                                         space->Size()));
       CHECK(bitmap.get() != NULL) << "Failed to create mod-union bitmap";
       bitmaps_.Put(space, bitmap.release());
     }
   }
 }

 ModUnionTableBitmap::~ModUnionTableBitmap() {
   STLDeleteValues(&bitmaps_);
 }

 void ModUnionTableBitmap::ClearCards(ContinuousSpace* space) {
   CardTable* card_table = heap_->GetCardTable();
   ModUnionClearCardVisitor visitor(&cleared_cards_);
   // Clear dirty cards in the this image space and update the corresponding mod-union bits.
   card_table->ModifyCardsAtomic(space->Begin(), space->End(), AgeCardVisitor(), visitor);
 }

 void ModUnionTableBitmap::Update() {
   CardTable* card_table = heap_->GetCardTable();
   while (!cleared_cards_.empty()) {
     byte* card = cleared_cards_.back();
     cleared_cards_.pop_back();

     uintptr_t start = reinterpret_cast<uintptr_t>(card_table->AddrFromCard(card));
     uintptr_t end = start + CardTable::kCardSize;
     ContinuousSpace* space = heap_->FindSpaceFromObject(reinterpret_cast<Object*>(start));
     SpaceBitmap* bitmap = space->GetLiveBitmap();

     // Clear the mod-union bitmap range corresponding to this card so that we don't have any
     // objects marked which do not reach the alloc space.
     bitmap->VisitRange(start, end, SpaceBitmap::ClearVisitor(bitmap));

     // At this point we need to update the mod-union bitmap to contain all the objects which reach
     // the alloc space.
     ModUnionVisitor visitor(heap_, bitmap);
     space->GetLiveBitmap()->VisitMarkedRange(start, end, visitor, VoidFunctor());
   }
 }

 class ModUnionScanImageRootVisitor {
  public:
   ModUnionScanImageRootVisitor(MarkSweep* const mark_sweep) : mark_sweep_(mark_sweep) {
   }

   void operator ()(const Object* root) const
       EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     DCHECK(root != NULL);
     mark_sweep_->ScanRoot(root);
   }

  private:
   MarkSweep* const mark_sweep_;
 };

 void ModUnionTableBitmap::MarkReferences(MarkSweep* mark_sweep) {
   // Some tests have no image space, and therefore no mod-union bitmap.
   ModUnionScanImageRootVisitor image_root_scanner(mark_sweep);
   for (BitmapMap::iterator it = bitmaps_.begin(); it != bitmaps_.end(); ++it) {
     const ContinuousSpace* space = it->first;
     uintptr_t begin = reinterpret_cast<uintptr_t>(space->Begin());
     uintptr_t end = reinterpret_cast<uintptr_t>(space->End());
     it->second->VisitMarkedRange(begin, end, image_root_scanner, VoidFunctor());
   }
 }


 ModUnionTableReferenceCache::ModUnionTableReferenceCache(Heap* heap) : ModUnionTable(heap) {

 }

 ModUnionTableReferenceCache::~ModUnionTableReferenceCache() {

 }

 void ModUnionTableReferenceCache::ClearCards(ContinuousSpace* space) {
   CardTable* card_table = GetHeap()->GetCardTable();
   ModUnionClearCardSetVisitor visitor(&cleared_cards_);
   // Clear dirty cards in the this space and update the corresponding mod-union bits.
   card_table->ModifyCardsAtomic(space->Begin(), space->End(), AgeCardVisitor(), visitor);
 }

 class AddToReferenceArrayVisitor {
  public:
   explicit AddToReferenceArrayVisitor(
       ModUnionTableReferenceCache* const mod_union_table,
         ModUnionTableReferenceCache::ReferenceArray* references)
     : mod_union_table_(mod_union_table),
       references_(references) {
   }

   // Extra parameters are required since we use this same visitor signature for checking objects.
   void operator ()(const Object* obj, const Object* ref, const MemberOffset& /* offset */,
                      bool /* is_static */) const {
     // Only add the reference if it is non null and fits our criteria.
     if (ref != NULL && mod_union_table_->AddReference(obj, ref)) {
       references_->push_back(ref);
     }
   }

  private:
   ModUnionTableReferenceCache* mod_union_table_;
   ModUnionTable::ReferenceArray* references_;
 };

 class ModUnionReferenceVisitor {
  public:
   explicit ModUnionReferenceVisitor(
         ModUnionTableReferenceCache* const mod_union_table,
         ModUnionTableReferenceCache::ReferenceArray* references)
     : mod_union_table_(mod_union_table),
       references_(references) {
   }

   void operator ()(const Object* obj) const
       SHARED_LOCKS_REQUIRED(Locks::heap_bitmap_lock_,
                             Locks::mutator_lock_) {
     DCHECK(obj != NULL);
     // We don't have an early exit since we use the visitor pattern, an early
     // exit should significantly speed this up.
     AddToReferenceArrayVisitor visitor(mod_union_table_, references_);
     MarkSweep::VisitObjectReferences(obj, visitor);
   }
  private:
   ModUnionTableReferenceCache* const mod_union_table_;
   ModUnionTable::ReferenceArray* references_;
 };


 class CheckReferenceVisitor {
  public:
   typedef std::set<const Object*> ReferenceSet;

   explicit CheckReferenceVisitor(
       ModUnionTableReferenceCache* const mod_union_table,
       const ReferenceSet& references)
     : mod_union_table_(mod_union_table),
       references_(references) {
   }

   // Extra parameters are required since we use this same visitor signature for checking objects.
   // TODO: Fixme when anotatalysis works with visitors.
   void operator ()(const Object* obj, const Object* ref, const MemberOffset& /* offset */,
                      bool /* is_static */) const
       SHARED_LOCKS_REQUIRED(Locks::heap_bitmap_lock_) {
     Heap* heap = mod_union_table_->GetHeap();
     if (ref != NULL && mod_union_table_->AddReference(obj, ref) &&
         references_.find(ref) == references_.end()) {
       ContinuousSpace* from_space = heap->FindSpaceFromObject(obj);
       ContinuousSpace* to_space = heap->FindSpaceFromObject(ref);
       LOG(INFO) << "Object " << reinterpret_cast<const void*>(obj) << "(" << PrettyTypeOf(obj) << ")"
                 << "References " << reinterpret_cast<const void*>(ref)
                 << "(" << PrettyTypeOf(ref) << ") without being in mod-union table";
       LOG(INFO) << "FromSpace " << from_space->GetName() << " type " << from_space->GetGcRetentionPolicy();
       LOG(INFO) << "ToSpace " << to_space->GetName() << " type " << to_space->GetGcRetentionPolicy();
       mod_union_table_->GetHeap()->DumpSpaces();
       LOG(FATAL) << "FATAL ERROR";
     }
   }

  private:
   ModUnionTableReferenceCache* const mod_union_table_;
   const ReferenceSet& references_;
 };

 class ModUnionCheckReferences {
  public:
   typedef std::set<const Object*> ReferenceSet;

   explicit ModUnionCheckReferences (
       ModUnionTableReferenceCache* const mod_union_table,
       const ReferenceSet& references)
     : mod_union_table_(mod_union_table),
       references_(references) {
   }

   void operator ()(const Object* obj) const NO_THREAD_SAFETY_ANALYSIS {
     DCHECK(obj != NULL);
     if (kDebugLocking) {
       Locks::heap_bitmap_lock_->AssertSharedHeld(Thread::Current());
     }
     CheckReferenceVisitor visitor(mod_union_table_, references_);
     MarkSweep::VisitObjectReferences(obj, visitor);
   }

  private:
   ModUnionTableReferenceCache* const mod_union_table_;
   const ReferenceSet& references_;
 };

 void ModUnionTableReferenceCache::Verify() {
   // Start by checking that everything in the mod union table is marked.
   Heap* heap = GetHeap();
   for (ReferenceMap::const_iterator it = references_.begin(); it != references_.end(); ++it) {
     for (ReferenceArray::const_iterator it_ref = it->second.begin(); it_ref != it->second.end();
         ++it_ref ) {
       DCHECK(heap->GetLiveBitmap()->Test(*it_ref));
     }
   }

   // Check the references of each clean card which is also in the mod union table.
   for (ReferenceMap::const_iterator it = references_.begin(); it != references_.end(); ++it) {
     const byte* card = &*it->first;
     if (*card == CardTable::kCardClean) {
       std::set<const Object*> reference_set;
       for (ReferenceArray::const_iterator itr = it->second.begin(); itr != it->second.end();++itr) {
         reference_set.insert(*itr);
       }
       ModUnionCheckReferences visitor(this, reference_set);
       CardTable* card_table = heap->GetCardTable();
       uintptr_t start = reinterpret_cast<uintptr_t>(card_table->AddrFromCard(card));
       uintptr_t end = start + CardTable::kCardSize;
       SpaceBitmap* live_bitmap =
               heap->FindSpaceFromObject(reinterpret_cast<Object*>(start))->GetLiveBitmap();
       live_bitmap->VisitMarkedRange(start, end, visitor, VoidFunctor());
     }
   }
 }

 void ModUnionTableReferenceCache::Update() {
   Heap* heap = GetHeap();
   CardTable* card_table = heap->GetCardTable();

   ReferenceArray cards_references;
   ModUnionReferenceVisitor visitor(this, &cards_references);

   for (ClearedCards::iterator it = cleared_cards_.begin(); it != cleared_cards_.end(); ++it) {
     byte* card = *it;
     // Clear and re-compute alloc space references associated with this card.
     cards_references.clear();
     uintptr_t start = reinterpret_cast<uintptr_t>(card_table->AddrFromCard(card));
     uintptr_t end = start + CardTable::kCardSize;
     SpaceBitmap* live_bitmap =
         heap->FindSpaceFromObject(reinterpret_cast<Object*>(start))->GetLiveBitmap();
     live_bitmap->VisitMarkedRange(start, end, visitor, VoidFunctor());

     // Update the corresponding references for the card.
     // TODO: C++0x auto
     ReferenceMap::iterator found = references_.find(card);
     if (found == references_.end()) {
       if (cards_references.empty()) {
         // No reason to add empty array.
         continue;
       }
       references_.Put(card, cards_references);
     } else {
       found->second = cards_references;
     }
   }
   cleared_cards_.clear();
 }

 void ModUnionTableReferenceCache::MarkReferences(MarkSweep* mark_sweep) {
   // TODO: C++0x auto
   size_t count = 0;
   for (ReferenceMap::const_iterator it = references_.begin(); it != references_.end(); ++it) {
     for (ReferenceArray::const_iterator it_ref = it->second.begin(); it_ref != it->second.end(); ++it_ref ) {
       mark_sweep->MarkRoot(*it_ref);
       ++count;
     }
   }
   if (VLOG_IS_ON(heap)) {
     VLOG(gc) << "Marked " << count << " references in mod union table";
   }
 }

 ModUnionTableCardCache::ModUnionTableCardCache(Heap* heap) : ModUnionTable(heap) {

 }

 ModUnionTableCardCache::~ModUnionTableCardCache() {

 }

 void ModUnionTableCardCache::ClearCards(ContinuousSpace* space) {
   CardTable* card_table = GetHeap()->GetCardTable();
   ModUnionClearCardSetVisitor visitor(&cleared_cards_);
   // Clear dirty cards in the this space and update the corresponding mod-union bits.
   card_table->ModifyCardsAtomic(space->Begin(), space->End(), AgeCardVisitor(), visitor);
 }

 // Mark all references to the alloc space(s).
 void ModUnionTableCardCache::MarkReferences(MarkSweep* mark_sweep) {
   CardTable* card_table = heap_->GetCardTable();
   ModUnionScanImageRootVisitor visitor(mark_sweep);
   for (ClearedCards::const_iterator it = cleared_cards_.begin(); it != cleared_cards_.end(); ++it) {
     byte* card = *it;
     uintptr_t start = reinterpret_cast<uintptr_t>(card_table->AddrFromCard(card));
     uintptr_t end = start + CardTable::kCardSize;
     SpaceBitmap* live_bitmap =
         heap_->FindSpaceFromObject(reinterpret_cast<Object*>(start))->GetLiveBitmap();
     live_bitmap->VisitMarkedRange(start, end, visitor, VoidFunctor());
   }
 }

 }  // namespace art
	/*
	* Copyright (C) 2012 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#include "heap.h"
	#include "heap_bitmap.h"
	#include "mark_sweep.h"
	#include "mod_union_table.h"
	#include "space.h"
	#include "stl_util.h"
	#include "UniquePtr.h"

	namespace art {

	class MarkIfReachesAllocspaceVisitor {
	public:
	explicit MarkIfReachesAllocspaceVisitor(Heap* const heap, SpaceBitmap* bitmap)
	: heap_(heap),
	bitmap_(bitmap) {
	}

	// Extra parameters are required since we use this same visitor signature for checking objects.
	void operator ()(const Object* obj, const Object* ref, const MemberOffset& /* offset /, bool / is_static */) const {
	// TODO: Optimize?
	// TODO: C++0x auto
	const Spaces& spaces = heap_->GetSpaces();
	for (Spaces::const_iterator cur = spaces.begin(); cur != spaces.end(); ++cur) {
	if ((cur)->IsAllocSpace() && (cur)->Contains(ref)) {
	bitmap_->Set(obj);
	break;
	}
	}
	}

	private:
	Heap* const heap_;
	SpaceBitmap* bitmap_;
	};

	class ModUnionVisitor {
	public:
	explicit ModUnionVisitor(Heap* const heap, SpaceBitmap* bitmap)
	: heap_(heap),
	bitmap_(bitmap) {
	}

	void operator ()(const Object* obj) const
	SHARED_LOCKS_REQUIRED(Locks::heap_bitmap_lock_,
	Locks::mutator_lock_) {
	DCHECK(obj != NULL);
	// We don't have an early exit since we use the visitor pattern, an early exit should
	// significantly speed this up.
	MarkIfReachesAllocspaceVisitor visitor(heap_, bitmap_);
	MarkSweep::VisitObjectReferences(obj, visitor);
	}
	private:
	Heap* const heap_;
	SpaceBitmap* bitmap_;
	};

	class ModUnionClearCardSetVisitor {
	public:
	explicit ModUnionClearCardSetVisitor(std::set<byte> const cleared_cards)
	: cleared_cards_(cleared_cards) {
	}

	inline void operator ()(byte* card, byte expected_value, byte new_value) const {
	if (expected_value == CardTable::kCardDirty) {
	cleared_cards_->insert(card);
	}
	}

	private:
	std::set<byte> const cleared_cards_;
	};

	class ModUnionClearCardVisitor {
	public:
	explicit ModUnionClearCardVisitor(std::vector<byte> cleared_cards)
	: cleared_cards_(cleared_cards) {
	}

	void operator ()(byte* card, byte expected_card, byte new_card) const {
	if (expected_card == CardTable::kCardDirty) {
	cleared_cards_->push_back(card);
	}
	}
	private:
	std::vector<byte> cleared_cards_;
	};

	ModUnionTableBitmap::ModUnionTableBitmap(Heap* heap) : ModUnionTable(heap) {
	// Prevent fragmentation of the heap which is caused by resizing of the vector.
	// TODO: Make a new vector which uses madvise (basically same as a mark stack).
	cleared_cards_.reserve(32);
	const Spaces& spaces = heap->GetSpaces();
	// Create one heap bitmap per image space.
	// TODO: C++0x auto
	for (Spaces::const_iterator it = spaces.begin(); it != spaces.end(); ++it) {
	ContinuousSpace* space = *it;
	if (space->IsImageSpace()) {
	// The mod-union table is only needed when we have an image space since it's purpose is to
	// cache image roots.
	UniquePtr<SpaceBitmap> bitmap(SpaceBitmap::Create("mod-union table bitmap", space->Begin(),
	space->Size()));
	CHECK(bitmap.get() != NULL) << "Failed to create mod-union bitmap";
	bitmaps_.Put(space, bitmap.release());
	}
	}
	}

	ModUnionTableBitmap::~ModUnionTableBitmap() {
	STLDeleteValues(&bitmaps_);
	}

	void ModUnionTableBitmap::ClearCards(ContinuousSpace* space) {
	CardTable* card_table = heap_->GetCardTable();
	ModUnionClearCardVisitor visitor(&cleared_cards_);
	// Clear dirty cards in the this image space and update the corresponding mod-union bits.
	card_table->ModifyCardsAtomic(space->Begin(), space->End(), AgeCardVisitor(), visitor);
	}

	void ModUnionTableBitmap::Update() {
	CardTable* card_table = heap_->GetCardTable();
	while (!cleared_cards_.empty()) {
	byte* card = cleared_cards_.back();
	cleared_cards_.pop_back();

	uintptr_t start = reinterpret_cast<uintptr_t>(card_table->AddrFromCard(card));
	uintptr_t end = start + CardTable::kCardSize;
	ContinuousSpace* space = heap_->FindSpaceFromObject(reinterpret_cast<Object*>(start));
	SpaceBitmap* bitmap = space->GetLiveBitmap();

	// Clear the mod-union bitmap range corresponding to this card so that we don't have any
	// objects marked which do not reach the alloc space.
	bitmap->VisitRange(start, end, SpaceBitmap::ClearVisitor(bitmap));

	// At this point we need to update the mod-union bitmap to contain all the objects which reach
	// the alloc space.
	ModUnionVisitor visitor(heap_, bitmap);
	space->GetLiveBitmap()->VisitMarkedRange(start, end, visitor, VoidFunctor());
	}
	}

	class ModUnionScanImageRootVisitor {
	public:
	ModUnionScanImageRootVisitor(MarkSweep* const mark_sweep) : mark_sweep_(mark_sweep) {
	}

	void operator ()(const Object* root) const
	EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_)
	SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
	DCHECK(root != NULL);
	mark_sweep_->ScanRoot(root);
	}

	private:
	MarkSweep* const mark_sweep_;
	};

	void ModUnionTableBitmap::MarkReferences(MarkSweep* mark_sweep) {
	// Some tests have no image space, and therefore no mod-union bitmap.
	ModUnionScanImageRootVisitor image_root_scanner(mark_sweep);
	for (BitmapMap::iterator it = bitmaps_.begin(); it != bitmaps_.end(); ++it) {
	const ContinuousSpace* space = it->first;
	uintptr_t begin = reinterpret_cast<uintptr_t>(space->Begin());
	uintptr_t end = reinterpret_cast<uintptr_t>(space->End());
	it->second->VisitMarkedRange(begin, end, image_root_scanner, VoidFunctor());
	}
	}


	ModUnionTableReferenceCache::ModUnionTableReferenceCache(Heap* heap) : ModUnionTable(heap) {

	}

	ModUnionTableReferenceCache::~ModUnionTableReferenceCache() {

	}

	void ModUnionTableReferenceCache::ClearCards(ContinuousSpace* space) {
	CardTable* card_table = GetHeap()->GetCardTable();
	ModUnionClearCardSetVisitor visitor(&cleared_cards_);
	// Clear dirty cards in the this space and update the corresponding mod-union bits.
	card_table->ModifyCardsAtomic(space->Begin(), space->End(), AgeCardVisitor(), visitor);
	}

	class AddToReferenceArrayVisitor {
	public:
	explicit AddToReferenceArrayVisitor(
	ModUnionTableReferenceCache* const mod_union_table,
	ModUnionTableReferenceCache::ReferenceArray* references)
	: mod_union_table_(mod_union_table),
	references_(references) {
	}

	// Extra parameters are required since we use this same visitor signature for checking objects.
	void operator ()(const Object* obj, const Object* ref, const MemberOffset& /* offset */,
	bool /* is_static */) const {
	// Only add the reference if it is non null and fits our criteria.
	if (ref != NULL && mod_union_table_->AddReference(obj, ref)) {
	references_->push_back(ref);
	}
	}

	private:
	ModUnionTableReferenceCache* mod_union_table_;
	ModUnionTable::ReferenceArray* references_;
	};

	class ModUnionReferenceVisitor {
	public:
	explicit ModUnionReferenceVisitor(
	ModUnionTableReferenceCache* const mod_union_table,
	ModUnionTableReferenceCache::ReferenceArray* references)
	: mod_union_table_(mod_union_table),
	references_(references) {
	}

	void operator ()(const Object* obj) const
	SHARED_LOCKS_REQUIRED(Locks::heap_bitmap_lock_,
	Locks::mutator_lock_) {
	DCHECK(obj != NULL);
	// We don't have an early exit since we use the visitor pattern, an early
	// exit should significantly speed this up.
	AddToReferenceArrayVisitor visitor(mod_union_table_, references_);
	MarkSweep::VisitObjectReferences(obj, visitor);
	}
	private:
	ModUnionTableReferenceCache* const mod_union_table_;
	ModUnionTable::ReferenceArray* references_;
	};


	class CheckReferenceVisitor {
	public:
	typedef std::set<const Object*> ReferenceSet;

	explicit CheckReferenceVisitor(
	ModUnionTableReferenceCache* const mod_union_table,
	const ReferenceSet& references)
	: mod_union_table_(mod_union_table),
	references_(references) {
	}

	// Extra parameters are required since we use this same visitor signature for checking objects.
	// TODO: Fixme when anotatalysis works with visitors.
	void operator ()(const Object* obj, const Object* ref, const MemberOffset& /* offset */,
	bool /* is_static */) const
	SHARED_LOCKS_REQUIRED(Locks::heap_bitmap_lock_) {
	Heap* heap = mod_union_table_->GetHeap();
	if (ref != NULL && mod_union_table_->AddReference(obj, ref) &&
	references_.find(ref) == references_.end()) {
	ContinuousSpace* from_space = heap->FindSpaceFromObject(obj);
	ContinuousSpace* to_space = heap->FindSpaceFromObject(ref);
	LOG(INFO) << "Object " << reinterpret_cast<const void*>(obj) << "(" << PrettyTypeOf(obj) << ")"
	<< "References " << reinterpret_cast<const void*>(ref)
	<< "(" << PrettyTypeOf(ref) << ") without being in mod-union table";
	LOG(INFO) << "FromSpace " << from_space->GetName() << " type " << from_space->GetGcRetentionPolicy();
	LOG(INFO) << "ToSpace " << to_space->GetName() << " type " << to_space->GetGcRetentionPolicy();
	mod_union_table_->GetHeap()->DumpSpaces();
	LOG(FATAL) << "FATAL ERROR";
	}
	}

	private:
	ModUnionTableReferenceCache* const mod_union_table_;
	const ReferenceSet& references_;
	};

	class ModUnionCheckReferences {
	public:
	typedef std::set<const Object*> ReferenceSet;

	explicit ModUnionCheckReferences (
	ModUnionTableReferenceCache* const mod_union_table,
	const ReferenceSet& references)
	: mod_union_table_(mod_union_table),
	references_(references) {
	}

	void operator ()(const Object* obj) const NO_THREAD_SAFETY_ANALYSIS {
	DCHECK(obj != NULL);
	if (kDebugLocking) {
	Locks::heap_bitmap_lock_->AssertSharedHeld(Thread::Current());
	}
	CheckReferenceVisitor visitor(mod_union_table_, references_);
	MarkSweep::VisitObjectReferences(obj, visitor);
	}

	private:
	ModUnionTableReferenceCache* const mod_union_table_;
	const ReferenceSet& references_;
	};

	void ModUnionTableReferenceCache::Verify() {
	// Start by checking that everything in the mod union table is marked.
	Heap* heap = GetHeap();
	for (ReferenceMap::const_iterator it = references_.begin(); it != references_.end(); ++it) {
	for (ReferenceArray::const_iterator it_ref = it->second.begin(); it_ref != it->second.end();
	++it_ref ) {
	DCHECK(heap->GetLiveBitmap()->Test(*it_ref));
	}
	}

	// Check the references of each clean card which is also in the mod union table.
	for (ReferenceMap::const_iterator it = references_.begin(); it != references_.end(); ++it) {
	const byte* card = &*it->first;
	if (*card == CardTable::kCardClean) {
	std::set<const Object*> reference_set;
	for (ReferenceArray::const_iterator itr = it->second.begin(); itr != it->second.end();++itr) {
	reference_set.insert(*itr);
	}
	ModUnionCheckReferences visitor(this, reference_set);
	CardTable* card_table = heap->GetCardTable();
	uintptr_t start = reinterpret_cast<uintptr_t>(card_table->AddrFromCard(card));
	uintptr_t end = start + CardTable::kCardSize;
	SpaceBitmap* live_bitmap =
	heap->FindSpaceFromObject(reinterpret_cast<Object*>(start))->GetLiveBitmap();
	live_bitmap->VisitMarkedRange(start, end, visitor, VoidFunctor());
	}
	}
	}

	void ModUnionTableReferenceCache::Update() {
	Heap* heap = GetHeap();
	CardTable* card_table = heap->GetCardTable();

	ReferenceArray cards_references;
	ModUnionReferenceVisitor visitor(this, &cards_references);

	for (ClearedCards::iterator it = cleared_cards_.begin(); it != cleared_cards_.end(); ++it) {
	byte* card = *it;
	// Clear and re-compute alloc space references associated with this card.
	cards_references.clear();
	uintptr_t start = reinterpret_cast<uintptr_t>(card_table->AddrFromCard(card));
	uintptr_t end = start + CardTable::kCardSize;
	SpaceBitmap* live_bitmap =
	heap->FindSpaceFromObject(reinterpret_cast<Object*>(start))->GetLiveBitmap();
	live_bitmap->VisitMarkedRange(start, end, visitor, VoidFunctor());

	// Update the corresponding references for the card.
	// TODO: C++0x auto
	ReferenceMap::iterator found = references_.find(card);
	if (found == references_.end()) {
	if (cards_references.empty()) {
	// No reason to add empty array.
	continue;
	}
	references_.Put(card, cards_references);
	} else {
	found->second = cards_references;
	}
	}
	cleared_cards_.clear();
	}

	void ModUnionTableReferenceCache::MarkReferences(MarkSweep* mark_sweep) {
	// TODO: C++0x auto
	size_t count = 0;
	for (ReferenceMap::const_iterator it = references_.begin(); it != references_.end(); ++it) {
	for (ReferenceArray::const_iterator it_ref = it->second.begin(); it_ref != it->second.end(); ++it_ref ) {
	mark_sweep->MarkRoot(*it_ref);
	++count;
	}
	}
	if (VLOG_IS_ON(heap)) {
	VLOG(gc) << "Marked " << count << " references in mod union table";
	}
	}

	ModUnionTableCardCache::ModUnionTableCardCache(Heap* heap) : ModUnionTable(heap) {

	}

	ModUnionTableCardCache::~ModUnionTableCardCache() {

	}

	void ModUnionTableCardCache::ClearCards(ContinuousSpace* space) {
	CardTable* card_table = GetHeap()->GetCardTable();
	ModUnionClearCardSetVisitor visitor(&cleared_cards_);
	// Clear dirty cards in the this space and update the corresponding mod-union bits.
	card_table->ModifyCardsAtomic(space->Begin(), space->End(), AgeCardVisitor(), visitor);
	}

	// Mark all references to the alloc space(s).
	void ModUnionTableCardCache::MarkReferences(MarkSweep* mark_sweep) {
	CardTable* card_table = heap_->GetCardTable();
	ModUnionScanImageRootVisitor visitor(mark_sweep);
	for (ClearedCards::const_iterator it = cleared_cards_.begin(); it != cleared_cards_.end(); ++it) {
	byte* card = *it;
	uintptr_t start = reinterpret_cast<uintptr_t>(card_table->AddrFromCard(card));
	uintptr_t end = start + CardTable::kCardSize;
	SpaceBitmap* live_bitmap =
	heap_->FindSpaceFromObject(reinterpret_cast<Object*>(start))->GetLiveBitmap();
	live_bitmap->VisitMarkedRange(start, end, visitor, VoidFunctor());
	}
	}

	} // namespace art