runtime/gc/accounting/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 "mod_union_table.h"

 #include "base/stl_util.h"
 #include "card_table-inl.h"
 #include "heap_bitmap.h"
 #include "gc/collector/mark_sweep-inl.h"
 #include "gc/heap.h"
 #include "gc/space/space.h"
 #include "mirror/object-inl.h"
 #include "mirror/class-inl.h"
 #include "mirror/field-inl.h"
 #include "mirror/object_array-inl.h"
 #include "space_bitmap-inl.h"
 #include "thread.h"
 #include "UniquePtr.h"

 using namespace art::mirror;

 namespace art {
 namespace gc {
 namespace accounting {

 class MarkIfReachesAllocspaceVisitor {
  public:
   explicit MarkIfReachesAllocspaceVisitor(Heap* const heap, accounting::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 std::vector<space::ContinuousSpace*>& spaces = heap_->GetContinuousSpaces();
     typedef std::vector<space::ContinuousSpace*>::const_iterator It;
     for (It cur = spaces.begin(); cur != spaces.end(); ++cur) {
       if ((*cur)->IsDlMallocSpace() && (*cur)->Contains(ref)) {
         bitmap_->Set(obj);
         break;
       }
     }
   }

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

 class ModUnionVisitor {
  public:
   explicit ModUnionVisitor(Heap* const heap, accounting::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_);
     collector::MarkSweep::VisitObjectReferences(obj, visitor);
   }
  private:
   Heap* const heap_;
   accounting::SpaceBitmap* const 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*>* const cleared_cards_;
 };

 class ModUnionScanImageRootVisitor {
  public:
   explicit ModUnionScanImageRootVisitor(collector::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:
   collector::MarkSweep* const mark_sweep_;
 };

 void ModUnionTableReferenceCache::ClearCards(space::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* mod_union_table,
                                       std::vector<const mirror::Object*>* 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* const mod_union_table_;
   std::vector<const mirror::Object*>* const references_;
 };

 class ModUnionReferenceVisitor {
  public:
   explicit ModUnionReferenceVisitor(ModUnionTableReferenceCache* const mod_union_table,
                                     std::vector<const mirror::Object*>* 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_);
     collector::MarkSweep::VisitObjectReferences(obj, visitor);
   }
  private:
   ModUnionTableReferenceCache* const mod_union_table_;
   std::vector<const mirror::Object*>* const references_;
 };

 class CheckReferenceVisitor {
  public:
   explicit CheckReferenceVisitor(ModUnionTableReferenceCache* mod_union_table,
                                  const std::set<const Object*>& 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_, Locks::mutator_lock_) {
     Heap* heap = mod_union_table_->GetHeap();
     if (ref != NULL && mod_union_table_->AddReference(obj, ref) &&
         references_.find(ref) == references_.end()) {
       space::ContinuousSpace* from_space = heap->FindContinuousSpaceFromObject(obj, false);
       space::ContinuousSpace* to_space = heap->FindContinuousSpaceFromObject(ref, false);
       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 std::set<const Object*>& references_;
 };

 class ModUnionCheckReferences {
  public:
   explicit ModUnionCheckReferences(ModUnionTableReferenceCache* mod_union_table,
                                    const std::set<const Object*>& references)
       EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_)
       : mod_union_table_(mod_union_table), references_(references) {
   }

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

  private:
   ModUnionTableReferenceCache* const mod_union_table_;
   const std::set<const Object*>& references_;
 };

 void ModUnionTableReferenceCache::Verify() {
   // Start by checking that everything in the mod union table is marked.
   Heap* heap = GetHeap();
   typedef SafeMap<const byte*, std::vector<const mirror::Object*> >::const_iterator It;
   typedef std::vector<const mirror::Object*>::const_iterator It2;
   for (It it = references_.begin(), end = references_.end(); it != end; ++it) {
     for (It2 it_ref = it->second.begin(), end_ref = it->second.end(); it_ref != end_ref;
         ++it_ref ) {
       CHECK(heap->IsLiveObjectLocked(*it_ref));
     }
   }

   // Check the references of each clean card which is also in the mod union table.
   CardTable* card_table = heap->GetCardTable();
   for (It it = references_.begin(); it != references_.end(); ++it) {
     const byte* card = &*it->first;
     if (*card == CardTable::kCardClean) {
       std::set<const Object*> reference_set;
       for (It2 itr = it->second.begin(); itr != it->second.end();++itr) {
         reference_set.insert(*itr);
       }
       ModUnionCheckReferences visitor(this, reference_set);
       uintptr_t start = reinterpret_cast<uintptr_t>(card_table->AddrFromCard(card));
       uintptr_t end = start + CardTable::kCardSize;
       space::ContinuousSpace* space =
           heap->FindContinuousSpaceFromObject(reinterpret_cast<Object*>(start), false);
       SpaceBitmap* live_bitmap = space->GetLiveBitmap();
       live_bitmap->VisitMarkedRange(start, end, visitor, VoidFunctor());
     }
   }
 }

 void ModUnionTableReferenceCache::Dump(std::ostream& os) {
   CardTable* card_table = heap_->GetCardTable();
   typedef std::set<byte*>::const_iterator It;
   os << "ModUnionTable cleared cards: [";
   for (It 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;
     os << reinterpret_cast<void*>(start) << "-" << reinterpret_cast<void*>(end) << ",";
   }
   os << "]\nModUnionTable references: [";
   typedef SafeMap<const byte*, std::vector<const mirror::Object*> >::const_iterator It2;
   for (It2 it = references_.begin(); it != references_.end(); ++it) {
     const byte* card = &*it->first;
     uintptr_t start = reinterpret_cast<uintptr_t>(card_table->AddrFromCard(card));
     uintptr_t end = start + CardTable::kCardSize;
     os << reinterpret_cast<void*>(start) << "-" << reinterpret_cast<void*>(end) << "->{";
     typedef std::vector<const mirror::Object*>::const_iterator It3;
     for (It3 itr = it->second.begin(); itr != it->second.end();++itr) {
       os << reinterpret_cast<const void*>(*itr) << ",";
     }
     os << "},";
   }
 }

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

   std::vector<const mirror::Object*> cards_references;
   ModUnionReferenceVisitor visitor(this, &cards_references);

   typedef std::set<byte*>::iterator It;
   for (It it = cleared_cards_.begin(), cc_end = cleared_cards_.end(); it != cc_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->FindContinuousSpaceFromObject(reinterpret_cast<Object*>(start), false)->GetLiveBitmap();
     live_bitmap->VisitMarkedRange(start, end, visitor, VoidFunctor());

     // Update the corresponding references for the card.
     // TODO: C++0x auto
     SafeMap<const byte*, std::vector<const mirror::Object*> >::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(collector::MarkSweep* mark_sweep) {
   // TODO: C++0x auto
   size_t count = 0;

   typedef SafeMap<const byte*, std::vector<const mirror::Object*> >::const_iterator It;
   for (It it = references_.begin(); it != references_.end(); ++it) {
     typedef std::vector<const mirror::Object*>::const_iterator It2;
     for (It2 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";
   }
 }

 void ModUnionTableCardCache::ClearCards(space::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(collector::MarkSweep* mark_sweep) {
   CardTable* card_table = heap_->GetCardTable();
   ModUnionScanImageRootVisitor visitor(mark_sweep);
   typedef std::set<byte*>::const_iterator It;
   It it = cleared_cards_.begin();
   It cc_end = cleared_cards_.end();
   if (it != cc_end) {
     byte* card = *it;
     uintptr_t start = reinterpret_cast<uintptr_t>(card_table->AddrFromCard(card));
     uintptr_t end = start + CardTable::kCardSize;
     space::ContinuousSpace* cur_space =
         heap_->FindContinuousSpaceFromObject(reinterpret_cast<Object*>(start), false);
     accounting::SpaceBitmap* cur_live_bitmap = cur_space->GetLiveBitmap();
     cur_live_bitmap->VisitMarkedRange(start, end, visitor, VoidFunctor());
     for (++it; it != cc_end; ++it) {
       card = *it;
       start = reinterpret_cast<uintptr_t>(card_table->AddrFromCard(card));
       end = start + CardTable::kCardSize;
       if (UNLIKELY(!cur_space->Contains(reinterpret_cast<Object*>(start)))) {
         cur_space = heap_->FindContinuousSpaceFromObject(reinterpret_cast<Object*>(start), false);
         cur_live_bitmap = cur_space->GetLiveBitmap();
       }
       cur_live_bitmap->VisitMarkedRange(start, end, visitor, VoidFunctor());
     }
   }
 }

 void ModUnionTableCardCache::Dump(std::ostream& os) {
   CardTable* card_table = heap_->GetCardTable();
   typedef std::set<byte*>::const_iterator It;
   os << "ModUnionTable dirty cards: [";
   for (It 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;
     os << reinterpret_cast<void*>(start) << "-" << reinterpret_cast<void*>(end) << ",";
   }
   os << "]";
 }

 }  // namespace accounting
 }  // namespace gc
 }  // 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 "mod_union_table.h"

	#include "base/stl_util.h"
	#include "card_table-inl.h"
	#include "heap_bitmap.h"
	#include "gc/collector/mark_sweep-inl.h"
	#include "gc/heap.h"
	#include "gc/space/space.h"
	#include "mirror/object-inl.h"
	#include "mirror/class-inl.h"
	#include "mirror/field-inl.h"
	#include "mirror/object_array-inl.h"
	#include "space_bitmap-inl.h"
	#include "thread.h"
	#include "UniquePtr.h"

	using namespace art::mirror;

	namespace art {
	namespace gc {
	namespace accounting {

	class MarkIfReachesAllocspaceVisitor {
	public:
	explicit MarkIfReachesAllocspaceVisitor(Heap* const heap, accounting::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 std::vector<space::ContinuousSpace*>& spaces = heap_->GetContinuousSpaces();
	typedef std::vector<space::ContinuousSpace*>::const_iterator It;
	for (It cur = spaces.begin(); cur != spaces.end(); ++cur) {
	if ((cur)->IsDlMallocSpace() && (cur)->Contains(ref)) {
	bitmap_->Set(obj);
	break;
	}
	}
	}

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

	class ModUnionVisitor {
	public:
	explicit ModUnionVisitor(Heap* const heap, accounting::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_);
	collector::MarkSweep::VisitObjectReferences(obj, visitor);
	}
	private:
	Heap* const heap_;
	accounting::SpaceBitmap* const 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> const cleared_cards_;
	};

	class ModUnionScanImageRootVisitor {
	public:
	explicit ModUnionScanImageRootVisitor(collector::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:
	collector::MarkSweep* const mark_sweep_;
	};

	void ModUnionTableReferenceCache::ClearCards(space::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* mod_union_table,
	std::vector<const mirror::Object> 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* const mod_union_table_;
	std::vector<const mirror::Object> const references_;
	};

	class ModUnionReferenceVisitor {
	public:
	explicit ModUnionReferenceVisitor(ModUnionTableReferenceCache* const mod_union_table,
	std::vector<const mirror::Object> 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_);
	collector::MarkSweep::VisitObjectReferences(obj, visitor);
	}
	private:
	ModUnionTableReferenceCache* const mod_union_table_;
	std::vector<const mirror::Object> const references_;
	};

	class CheckReferenceVisitor {
	public:
	explicit CheckReferenceVisitor(ModUnionTableReferenceCache* mod_union_table,
	const std::set<const Object*>& 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_, Locks::mutator_lock_) {
	Heap* heap = mod_union_table_->GetHeap();
	if (ref != NULL && mod_union_table_->AddReference(obj, ref) &&
	references_.find(ref) == references_.end()) {
	space::ContinuousSpace* from_space = heap->FindContinuousSpaceFromObject(obj, false);
	space::ContinuousSpace* to_space = heap->FindContinuousSpaceFromObject(ref, false);
	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 std::set<const Object*>& references_;
	};

	class ModUnionCheckReferences {
	public:
	explicit ModUnionCheckReferences(ModUnionTableReferenceCache* mod_union_table,
	const std::set<const Object*>& references)
	EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_)
	: mod_union_table_(mod_union_table), references_(references) {
	}

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

	private:
	ModUnionTableReferenceCache* const mod_union_table_;
	const std::set<const Object*>& references_;
	};

	void ModUnionTableReferenceCache::Verify() {
	// Start by checking that everything in the mod union table is marked.
	Heap* heap = GetHeap();
	typedef SafeMap<const byte, std::vector<const mirror::Object> >::const_iterator It;
	typedef std::vector<const mirror::Object*>::const_iterator It2;
	for (It it = references_.begin(), end = references_.end(); it != end; ++it) {
	for (It2 it_ref = it->second.begin(), end_ref = it->second.end(); it_ref != end_ref;
	++it_ref ) {
	CHECK(heap->IsLiveObjectLocked(*it_ref));
	}
	}

	// Check the references of each clean card which is also in the mod union table.
	CardTable* card_table = heap->GetCardTable();
	for (It it = references_.begin(); it != references_.end(); ++it) {
	const byte* card = &*it->first;
	if (*card == CardTable::kCardClean) {
	std::set<const Object*> reference_set;
	for (It2 itr = it->second.begin(); itr != it->second.end();++itr) {
	reference_set.insert(*itr);
	}
	ModUnionCheckReferences visitor(this, reference_set);
	uintptr_t start = reinterpret_cast<uintptr_t>(card_table->AddrFromCard(card));
	uintptr_t end = start + CardTable::kCardSize;
	space::ContinuousSpace* space =
	heap->FindContinuousSpaceFromObject(reinterpret_cast<Object*>(start), false);
	SpaceBitmap* live_bitmap = space->GetLiveBitmap();
	live_bitmap->VisitMarkedRange(start, end, visitor, VoidFunctor());
	}
	}
	}

	void ModUnionTableReferenceCache::Dump(std::ostream& os) {
	CardTable* card_table = heap_->GetCardTable();
	typedef std::set<byte*>::const_iterator It;
	os << "ModUnionTable cleared cards: [";
	for (It 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;
	os << reinterpret_cast<void>(start) << "-" << reinterpret_cast<void>(end) << ",";
	}
	os << "]\nModUnionTable references: [";
	typedef SafeMap<const byte, std::vector<const mirror::Object> >::const_iterator It2;
	for (It2 it = references_.begin(); it != references_.end(); ++it) {
	const byte* card = &*it->first;
	uintptr_t start = reinterpret_cast<uintptr_t>(card_table->AddrFromCard(card));
	uintptr_t end = start + CardTable::kCardSize;
	os << reinterpret_cast<void>(start) << "-" << reinterpret_cast<void>(end) << "->{";
	typedef std::vector<const mirror::Object*>::const_iterator It3;
	for (It3 itr = it->second.begin(); itr != it->second.end();++itr) {
	os << reinterpret_cast<const void>(itr) << ",";
	}
	os << "},";
	}
	}

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

	std::vector<const mirror::Object*> cards_references;
	ModUnionReferenceVisitor visitor(this, &cards_references);

	typedef std::set<byte*>::iterator It;
	for (It it = cleared_cards_.begin(), cc_end = cleared_cards_.end(); it != cc_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->FindContinuousSpaceFromObject(reinterpret_cast<Object*>(start), false)->GetLiveBitmap();
	live_bitmap->VisitMarkedRange(start, end, visitor, VoidFunctor());

	// Update the corresponding references for the card.
	// TODO: C++0x auto
	SafeMap<const byte, std::vector<const mirror::Object> >::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(collector::MarkSweep* mark_sweep) {
	// TODO: C++0x auto
	size_t count = 0;

	typedef SafeMap<const byte, std::vector<const mirror::Object> >::const_iterator It;
	for (It it = references_.begin(); it != references_.end(); ++it) {
	typedef std::vector<const mirror::Object*>::const_iterator It2;
	for (It2 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";
	}
	}

	void ModUnionTableCardCache::ClearCards(space::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(collector::MarkSweep* mark_sweep) {
	CardTable* card_table = heap_->GetCardTable();
	ModUnionScanImageRootVisitor visitor(mark_sweep);
	typedef std::set<byte*>::const_iterator It;
	It it = cleared_cards_.begin();
	It cc_end = cleared_cards_.end();
	if (it != cc_end) {
	byte* card = *it;
	uintptr_t start = reinterpret_cast<uintptr_t>(card_table->AddrFromCard(card));
	uintptr_t end = start + CardTable::kCardSize;
	space::ContinuousSpace* cur_space =
	heap_->FindContinuousSpaceFromObject(reinterpret_cast<Object*>(start), false);
	accounting::SpaceBitmap* cur_live_bitmap = cur_space->GetLiveBitmap();
	cur_live_bitmap->VisitMarkedRange(start, end, visitor, VoidFunctor());
	for (++it; it != cc_end; ++it) {
	card = *it;
	start = reinterpret_cast<uintptr_t>(card_table->AddrFromCard(card));
	end = start + CardTable::kCardSize;
	if (UNLIKELY(!cur_space->Contains(reinterpret_cast<Object*>(start)))) {
	cur_space = heap_->FindContinuousSpaceFromObject(reinterpret_cast<Object*>(start), false);
	cur_live_bitmap = cur_space->GetLiveBitmap();
	}
	cur_live_bitmap->VisitMarkedRange(start, end, visitor, VoidFunctor());
	}
	}
	}

	void ModUnionTableCardCache::Dump(std::ostream& os) {
	CardTable* card_table = heap_->GetCardTable();
	typedef std::set<byte*>::const_iterator It;
	os << "ModUnionTable dirty cards: [";
	for (It 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;
	os << reinterpret_cast<void>(start) << "-" << reinterpret_cast<void>(end) << ",";
	}
	os << "]";
	}

	} // namespace accounting
	} // namespace gc
	} // namespace art