runtime/intern_table.cc - platform/art - Git at Google

 /*
  * Copyright (C) 2011 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 "intern_table.h"

 #include <memory>

 #include "gc_root-inl.h"
 #include "gc/collector/garbage_collector.h"
 #include "gc/space/image_space.h"
 #include "gc/weak_root_state.h"
 #include "mirror/dex_cache-inl.h"
 #include "mirror/object_array-inl.h"
 #include "mirror/object-inl.h"
 #include "mirror/string-inl.h"
 #include "thread.h"
 #include "utf.h"

 namespace art {

 InternTable::InternTable()
     : images_added_to_intern_table_(false),
       log_new_roots_(false),
       weak_intern_condition_("New intern condition", *Locks::intern_table_lock_),
       weak_root_state_(gc::kWeakRootStateNormal) {
 }

 size_t InternTable::Size() const {
   MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
   return strong_interns_.Size() + weak_interns_.Size();
 }

 size_t InternTable::StrongSize() const {
   MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
   return strong_interns_.Size();
 }

 size_t InternTable::WeakSize() const {
   MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
   return weak_interns_.Size();
 }

 void InternTable::DumpForSigQuit(std::ostream& os) const {
   os << "Intern table: " << StrongSize() << " strong; " << WeakSize() << " weak\n";
 }

 void InternTable::VisitRoots(RootVisitor* visitor, VisitRootFlags flags) {
   MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
   if ((flags & kVisitRootFlagAllRoots) != 0) {
     strong_interns_.VisitRoots(visitor);
   } else if ((flags & kVisitRootFlagNewRoots) != 0) {
     for (auto& root : new_strong_intern_roots_) {
       mirror::String* old_ref = root.Read<kWithoutReadBarrier>();
       root.VisitRoot(visitor, RootInfo(kRootInternedString));
       mirror::String* new_ref = root.Read<kWithoutReadBarrier>();
       if (new_ref != old_ref) {
         // The GC moved a root in the log. Need to search the strong interns and update the
         // corresponding object. This is slow, but luckily for us, this may only happen with a
         // concurrent moving GC.
         strong_interns_.Remove(old_ref);
         strong_interns_.Insert(new_ref);
       }
     }
   }
   if ((flags & kVisitRootFlagClearRootLog) != 0) {
     new_strong_intern_roots_.clear();
   }
   if ((flags & kVisitRootFlagStartLoggingNewRoots) != 0) {
     log_new_roots_ = true;
   } else if ((flags & kVisitRootFlagStopLoggingNewRoots) != 0) {
     log_new_roots_ = false;
   }
   // Note: we deliberately don't visit the weak_interns_ table and the immutable image roots.
 }

 mirror::String* InternTable::LookupStrong(mirror::String* s) {
   return strong_interns_.Find(s);
 }

 mirror::String* InternTable::LookupWeak(mirror::String* s) {
   return weak_interns_.Find(s);
 }

 void InternTable::AddNewTable() {
   MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
   weak_interns_.AddNewTable();
   strong_interns_.AddNewTable();
 }

 mirror::String* InternTable::InsertStrong(mirror::String* s) {
   Runtime* runtime = Runtime::Current();
   if (runtime->IsActiveTransaction()) {
     runtime->RecordStrongStringInsertion(s);
   }
   if (log_new_roots_) {
     new_strong_intern_roots_.push_back(GcRoot<mirror::String>(s));
   }
   strong_interns_.Insert(s);
   return s;
 }

 mirror::String* InternTable::InsertWeak(mirror::String* s) {
   Runtime* runtime = Runtime::Current();
   if (runtime->IsActiveTransaction()) {
     runtime->RecordWeakStringInsertion(s);
   }
   weak_interns_.Insert(s);
   return s;
 }

 void InternTable::RemoveStrong(mirror::String* s) {
   strong_interns_.Remove(s);
 }

 void InternTable::RemoveWeak(mirror::String* s) {
   Runtime* runtime = Runtime::Current();
   if (runtime->IsActiveTransaction()) {
     runtime->RecordWeakStringRemoval(s);
   }
   weak_interns_.Remove(s);
 }

 // Insert/remove methods used to undo changes made during an aborted transaction.
 mirror::String* InternTable::InsertStrongFromTransaction(mirror::String* s) {
   DCHECK(!Runtime::Current()->IsActiveTransaction());
   return InsertStrong(s);
 }
 mirror::String* InternTable::InsertWeakFromTransaction(mirror::String* s) {
   DCHECK(!Runtime::Current()->IsActiveTransaction());
   return InsertWeak(s);
 }
 void InternTable::RemoveStrongFromTransaction(mirror::String* s) {
   DCHECK(!Runtime::Current()->IsActiveTransaction());
   RemoveStrong(s);
 }
 void InternTable::RemoveWeakFromTransaction(mirror::String* s) {
   DCHECK(!Runtime::Current()->IsActiveTransaction());
   RemoveWeak(s);
 }

 void InternTable::AddImagesStringsToTable(const std::vector<gc::space::ImageSpace*>& image_spaces) {
   MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
   for (gc::space::ImageSpace* image_space : image_spaces) {
     const ImageHeader* const header = &image_space->GetImageHeader();
     // Check if we have the interned strings section.
     const ImageSection& section = header->GetImageSection(ImageHeader::kSectionInternedStrings);
     if (section.Size() > 0) {
       AddTableFromMemoryLocked(image_space->Begin() + section.Offset());
     } else {
       // TODO: Delete this logic?
       mirror::Object* root = header->GetImageRoot(ImageHeader::kDexCaches);
       mirror::ObjectArray<mirror::DexCache>* dex_caches = root->AsObjectArray<mirror::DexCache>();
       for (int32_t i = 0; i < dex_caches->GetLength(); ++i) {
         mirror::DexCache* dex_cache = dex_caches->Get(i);
         const size_t num_strings = dex_cache->NumStrings();
         for (size_t j = 0; j < num_strings; ++j) {
           mirror::String* image_string = dex_cache->GetResolvedString(j);
           if (image_string != nullptr) {
             mirror::String* found = LookupStrong(image_string);
             if (found == nullptr) {
               InsertStrong(image_string);
             } else {
               DCHECK_EQ(found, image_string);
             }
           }
         }
       }
     }
   }
   images_added_to_intern_table_ = true;
 }

 mirror::String* InternTable::LookupStringFromImage(mirror::String* s) {
   DCHECK(!images_added_to_intern_table_);
   const std::vector<gc::space::ImageSpace*>& image_spaces =
       Runtime::Current()->GetHeap()->GetBootImageSpaces();
   if (image_spaces.empty()) {
     return nullptr;  // No image present.
   }
   const std::string utf8 = s->ToModifiedUtf8();
   for (gc::space::ImageSpace* image_space : image_spaces) {
     mirror::Object* root = image_space->GetImageHeader().GetImageRoot(ImageHeader::kDexCaches);
     mirror::ObjectArray<mirror::DexCache>* dex_caches = root->AsObjectArray<mirror::DexCache>();
     for (int32_t i = 0; i < dex_caches->GetLength(); ++i) {
       mirror::DexCache* dex_cache = dex_caches->Get(i);
       const DexFile* dex_file = dex_cache->GetDexFile();
       // Binary search the dex file for the string index.
       const DexFile::StringId* string_id = dex_file->FindStringId(utf8.c_str());
       if (string_id != nullptr) {
         uint32_t string_idx = dex_file->GetIndexForStringId(*string_id);
         // GetResolvedString() contains a RB.
         mirror::String* image_string = dex_cache->GetResolvedString(string_idx);
         if (image_string != nullptr) {
           return image_string;
         }
       }
     }
   }
   return nullptr;
 }

 void InternTable::BroadcastForNewInterns() {
   CHECK(kUseReadBarrier);
   Thread* self = Thread::Current();
   MutexLock mu(self, *Locks::intern_table_lock_);
   weak_intern_condition_.Broadcast(self);
 }

 void InternTable::WaitUntilAccessible(Thread* self) {
   Locks::intern_table_lock_->ExclusiveUnlock(self);
   {
     ScopedThreadSuspension sts(self, kWaitingWeakGcRootRead);
     MutexLock mu(self, *Locks::intern_table_lock_);
     while (weak_root_state_ == gc::kWeakRootStateNoReadsOrWrites) {
       weak_intern_condition_.Wait(self);
     }
   }
   Locks::intern_table_lock_->ExclusiveLock(self);
 }

 mirror::String* InternTable::Insert(mirror::String* s, bool is_strong, bool holding_locks) {
   if (s == nullptr) {
     return nullptr;
   }
   Thread* const self = Thread::Current();
   MutexLock mu(self, *Locks::intern_table_lock_);
   if (kDebugLocking && !holding_locks) {
     Locks::mutator_lock_->AssertSharedHeld(self);
     CHECK_EQ(2u, self->NumberOfHeldMutexes()) << "may only safely hold the mutator lock";
   }
   while (true) {
     if (holding_locks) {
       if (!kUseReadBarrier) {
         CHECK_EQ(weak_root_state_, gc::kWeakRootStateNormal);
       } else {
         CHECK(self->GetWeakRefAccessEnabled());
       }
     }
     // Check the strong table for a match.
     mirror::String* strong = LookupStrong(s);
     if (strong != nullptr) {
       return strong;
     }
     if ((!kUseReadBarrier && weak_root_state_ != gc::kWeakRootStateNoReadsOrWrites) ||
         (kUseReadBarrier && self->GetWeakRefAccessEnabled())) {
       break;
     }
     // weak_root_state_ is set to gc::kWeakRootStateNoReadsOrWrites in the GC pause but is only
     // cleared after SweepSystemWeaks has completed. This is why we need to wait until it is
     // cleared.
     CHECK(!holding_locks);
     StackHandleScope<1> hs(self);
     auto h = hs.NewHandleWrapper(&s);
     WaitUntilAccessible(self);
   }
   if (!kUseReadBarrier) {
     CHECK_EQ(weak_root_state_, gc::kWeakRootStateNormal);
   } else {
     CHECK(self->GetWeakRefAccessEnabled());
   }
   // There is no match in the strong table, check the weak table.
   mirror::String* weak = LookupWeak(s);
   if (weak != nullptr) {
     if (is_strong) {
       // A match was found in the weak table. Promote to the strong table.
       RemoveWeak(weak);
       return InsertStrong(weak);
     }
     return weak;
   }
   // Check the image for a match.
   if (!images_added_to_intern_table_) {
     mirror::String* const image_string = LookupStringFromImage(s);
     if (image_string != nullptr) {
       return is_strong ? InsertStrong(image_string) : InsertWeak(image_string);
     }
   }
   // No match in the strong table or the weak table. Insert into the strong / weak table.
   return is_strong ? InsertStrong(s) : InsertWeak(s);
 }

 mirror::String* InternTable::InternStrong(int32_t utf16_length, const char* utf8_data) {
   DCHECK(utf8_data != nullptr);
   return InternStrong(mirror::String::AllocFromModifiedUtf8(
       Thread::Current(), utf16_length, utf8_data));
 }

 mirror::String* InternTable::InternStrong(const char* utf8_data) {
   DCHECK(utf8_data != nullptr);
   return InternStrong(mirror::String::AllocFromModifiedUtf8(Thread::Current(), utf8_data));
 }

 mirror::String* InternTable::InternStrongImageString(mirror::String* s) {
   // May be holding the heap bitmap lock.
   return Insert(s, true, true);
 }

 mirror::String* InternTable::InternStrong(mirror::String* s) {
   return Insert(s, true, false);
 }

 mirror::String* InternTable::InternWeak(mirror::String* s) {
   return Insert(s, false, false);
 }

 bool InternTable::ContainsWeak(mirror::String* s) {
   MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
   return LookupWeak(s) == s;
 }

 void InternTable::SweepInternTableWeaks(IsMarkedVisitor* visitor) {
   MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
   weak_interns_.SweepWeaks(visitor);
 }

 size_t InternTable::AddTableFromMemory(const uint8_t* ptr) {
   MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
   return AddTableFromMemoryLocked(ptr);
 }

 size_t InternTable::AddTableFromMemoryLocked(const uint8_t* ptr) {
   return strong_interns_.AddTableFromMemory(ptr);
 }

 size_t InternTable::WriteToMemory(uint8_t* ptr) {
   MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
   return strong_interns_.WriteToMemory(ptr);
 }

 std::size_t InternTable::StringHashEquals::operator()(const GcRoot<mirror::String>& root) const {
   if (kIsDebugBuild) {
     Locks::mutator_lock_->AssertSharedHeld(Thread::Current());
   }
   return static_cast<size_t>(root.Read()->GetHashCode());
 }

 bool InternTable::StringHashEquals::operator()(const GcRoot<mirror::String>& a,
                                                const GcRoot<mirror::String>& b) const {
   if (kIsDebugBuild) {
     Locks::mutator_lock_->AssertSharedHeld(Thread::Current());
   }
   return a.Read()->Equals(b.Read());
 }

 size_t InternTable::Table::AddTableFromMemory(const uint8_t* ptr) {
   size_t read_count = 0;
   UnorderedSet set(ptr, /*make copy*/false, &read_count);
   // TODO: Disable this for app images if app images have intern tables.
   static constexpr bool kCheckDuplicates = true;
   if (kCheckDuplicates) {
     for (GcRoot<mirror::String>& string : set) {
       CHECK(Find(string.Read()) == nullptr) << "Already found " << string.Read()->ToModifiedUtf8();
     }
   }
   // Insert at the front since we insert into the back.
   tables_.insert(tables_.begin(), std::move(set));
   return read_count;
 }

 size_t InternTable::Table::WriteToMemory(uint8_t* ptr) {
   if (tables_.empty()) {
     return 0;
   }
   UnorderedSet* table_to_write;
   UnorderedSet combined;
   if (tables_.size() > 1) {
     table_to_write = &combined;
     for (UnorderedSet& table : tables_) {
       for (GcRoot<mirror::String>& string : table) {
         combined.Insert(string);
       }
     }
   } else {
     table_to_write = &tables_.back();
   }
   return table_to_write->WriteToMemory(ptr);
 }

 void InternTable::Table::Remove(mirror::String* s) {
   for (UnorderedSet& table : tables_) {
     auto it = table.Find(GcRoot<mirror::String>(s));
     if (it != table.end()) {
       table.Erase(it);
       return;
     }
   }
   LOG(FATAL) << "Attempting to remove non-interned string " << s->ToModifiedUtf8();
 }

 mirror::String* InternTable::Table::Find(mirror::String* s) {
   Locks::intern_table_lock_->AssertHeld(Thread::Current());
   for (UnorderedSet& table : tables_) {
     auto it = table.Find(GcRoot<mirror::String>(s));
     if (it != table.end()) {
       return it->Read();
     }
   }
   return nullptr;
 }

 void InternTable::Table::AddNewTable() {
   tables_.push_back(UnorderedSet());
 }

 void InternTable::Table::Insert(mirror::String* s) {
   // Always insert the last table, the image tables are before and we avoid inserting into these
   // to prevent dirty pages.
   DCHECK(!tables_.empty());
   tables_.back().Insert(GcRoot<mirror::String>(s));
 }

 void InternTable::Table::VisitRoots(RootVisitor* visitor) {
   BufferedRootVisitor<kDefaultBufferedRootCount> buffered_visitor(
       visitor, RootInfo(kRootInternedString));
   for (UnorderedSet& table : tables_) {
     for (auto& intern : table) {
       buffered_visitor.VisitRoot(intern);
     }
   }
 }

 void InternTable::Table::SweepWeaks(IsMarkedVisitor* visitor) {
   for (UnorderedSet& table : tables_) {
     SweepWeaks(&table, visitor);
   }
 }

 void InternTable::Table::SweepWeaks(UnorderedSet* set, IsMarkedVisitor* visitor) {
   for (auto it = set->begin(), end = set->end(); it != end;) {
     // This does not need a read barrier because this is called by GC.
     mirror::Object* object = it->Read<kWithoutReadBarrier>();
     mirror::Object* new_object = visitor->IsMarked(object);
     if (new_object == nullptr) {
       it = set->Erase(it);
     } else {
       *it = GcRoot<mirror::String>(new_object->AsString());
       ++it;
     }
   }
 }

 size_t InternTable::Table::Size() const {
   return std::accumulate(tables_.begin(),
                          tables_.end(),
                          0U,
                          [](size_t sum, const UnorderedSet& set) {
                            return sum + set.Size();
                          });
 }

 void InternTable::ChangeWeakRootState(gc::WeakRootState new_state) {
   MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
   ChangeWeakRootStateLocked(new_state);
 }

 void InternTable::ChangeWeakRootStateLocked(gc::WeakRootState new_state) {
   CHECK(!kUseReadBarrier);
   weak_root_state_ = new_state;
   if (new_state != gc::kWeakRootStateNoReadsOrWrites) {
     weak_intern_condition_.Broadcast(Thread::Current());
   }
 }

 InternTable::Table::Table() {
   Runtime* const runtime = Runtime::Current();
   // Initial table.
   tables_.push_back(UnorderedSet());
   tables_.back().SetLoadFactor(runtime->GetHashTableMinLoadFactor(),
                                runtime->GetHashTableMaxLoadFactor());
 }

 }  // namespace art
	/*
	* Copyright (C) 2011 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 "intern_table.h"

	#include <memory>

	#include "gc_root-inl.h"
	#include "gc/collector/garbage_collector.h"
	#include "gc/space/image_space.h"
	#include "gc/weak_root_state.h"
	#include "mirror/dex_cache-inl.h"
	#include "mirror/object_array-inl.h"
	#include "mirror/object-inl.h"
	#include "mirror/string-inl.h"
	#include "thread.h"
	#include "utf.h"

	namespace art {

	InternTable::InternTable()
	: images_added_to_intern_table_(false),
	log_new_roots_(false),
	weak_intern_condition_("New intern condition", *Locks::intern_table_lock_),
	weak_root_state_(gc::kWeakRootStateNormal) {
	}

	size_t InternTable::Size() const {
	MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
	return strong_interns_.Size() + weak_interns_.Size();
	}

	size_t InternTable::StrongSize() const {
	MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
	return strong_interns_.Size();
	}

	size_t InternTable::WeakSize() const {
	MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
	return weak_interns_.Size();
	}

	void InternTable::DumpForSigQuit(std::ostream& os) const {
	os << "Intern table: " << StrongSize() << " strong; " << WeakSize() << " weak\n";
	}

	void InternTable::VisitRoots(RootVisitor* visitor, VisitRootFlags flags) {
	MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
	if ((flags & kVisitRootFlagAllRoots) != 0) {
	strong_interns_.VisitRoots(visitor);
	} else if ((flags & kVisitRootFlagNewRoots) != 0) {
	for (auto& root : new_strong_intern_roots_) {
	mirror::String* old_ref = root.Read<kWithoutReadBarrier>();
	root.VisitRoot(visitor, RootInfo(kRootInternedString));
	mirror::String* new_ref = root.Read<kWithoutReadBarrier>();
	if (new_ref != old_ref) {
	// The GC moved a root in the log. Need to search the strong interns and update the
	// corresponding object. This is slow, but luckily for us, this may only happen with a
	// concurrent moving GC.
	strong_interns_.Remove(old_ref);
	strong_interns_.Insert(new_ref);
	}
	}
	}
	if ((flags & kVisitRootFlagClearRootLog) != 0) {
	new_strong_intern_roots_.clear();
	}
	if ((flags & kVisitRootFlagStartLoggingNewRoots) != 0) {
	log_new_roots_ = true;
	} else if ((flags & kVisitRootFlagStopLoggingNewRoots) != 0) {
	log_new_roots_ = false;
	}
	// Note: we deliberately don't visit the weak_interns_ table and the immutable image roots.
	}

	mirror::String* InternTable::LookupStrong(mirror::String* s) {
	return strong_interns_.Find(s);
	}

	mirror::String* InternTable::LookupWeak(mirror::String* s) {
	return weak_interns_.Find(s);
	}

	void InternTable::AddNewTable() {
	MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
	weak_interns_.AddNewTable();
	strong_interns_.AddNewTable();
	}

	mirror::String* InternTable::InsertStrong(mirror::String* s) {
	Runtime* runtime = Runtime::Current();
	if (runtime->IsActiveTransaction()) {
	runtime->RecordStrongStringInsertion(s);
	}
	if (log_new_roots_) {
	new_strong_intern_roots_.push_back(GcRoot<mirror::String>(s));
	}
	strong_interns_.Insert(s);
	return s;
	}

	mirror::String* InternTable::InsertWeak(mirror::String* s) {
	Runtime* runtime = Runtime::Current();
	if (runtime->IsActiveTransaction()) {
	runtime->RecordWeakStringInsertion(s);
	}
	weak_interns_.Insert(s);
	return s;
	}

	void InternTable::RemoveStrong(mirror::String* s) {
	strong_interns_.Remove(s);
	}

	void InternTable::RemoveWeak(mirror::String* s) {
	Runtime* runtime = Runtime::Current();
	if (runtime->IsActiveTransaction()) {
	runtime->RecordWeakStringRemoval(s);
	}
	weak_interns_.Remove(s);
	}

	// Insert/remove methods used to undo changes made during an aborted transaction.
	mirror::String* InternTable::InsertStrongFromTransaction(mirror::String* s) {
	DCHECK(!Runtime::Current()->IsActiveTransaction());
	return InsertStrong(s);
	}
	mirror::String* InternTable::InsertWeakFromTransaction(mirror::String* s) {
	DCHECK(!Runtime::Current()->IsActiveTransaction());
	return InsertWeak(s);
	}
	void InternTable::RemoveStrongFromTransaction(mirror::String* s) {
	DCHECK(!Runtime::Current()->IsActiveTransaction());
	RemoveStrong(s);
	}
	void InternTable::RemoveWeakFromTransaction(mirror::String* s) {
	DCHECK(!Runtime::Current()->IsActiveTransaction());
	RemoveWeak(s);
	}

	void InternTable::AddImagesStringsToTable(const std::vector<gc::space::ImageSpace*>& image_spaces) {
	MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
	for (gc::space::ImageSpace* image_space : image_spaces) {
	const ImageHeader* const header = &image_space->GetImageHeader();
	// Check if we have the interned strings section.
	const ImageSection& section = header->GetImageSection(ImageHeader::kSectionInternedStrings);
	if (section.Size() > 0) {
	AddTableFromMemoryLocked(image_space->Begin() + section.Offset());
	} else {
	// TODO: Delete this logic?
	mirror::Object* root = header->GetImageRoot(ImageHeader::kDexCaches);
	mirror::ObjectArray<mirror::DexCache>* dex_caches = root->AsObjectArray<mirror::DexCache>();
	for (int32_t i = 0; i < dex_caches->GetLength(); ++i) {
	mirror::DexCache* dex_cache = dex_caches->Get(i);
	const size_t num_strings = dex_cache->NumStrings();
	for (size_t j = 0; j < num_strings; ++j) {
	mirror::String* image_string = dex_cache->GetResolvedString(j);
	if (image_string != nullptr) {
	mirror::String* found = LookupStrong(image_string);
	if (found == nullptr) {
	InsertStrong(image_string);
	} else {
	DCHECK_EQ(found, image_string);
	}
	}
	}
	}
	}
	}
	images_added_to_intern_table_ = true;
	}

	mirror::String* InternTable::LookupStringFromImage(mirror::String* s) {
	DCHECK(!images_added_to_intern_table_);
	const std::vector<gc::space::ImageSpace*>& image_spaces =
	Runtime::Current()->GetHeap()->GetBootImageSpaces();
	if (image_spaces.empty()) {
	return nullptr; // No image present.
	}
	const std::string utf8 = s->ToModifiedUtf8();
	for (gc::space::ImageSpace* image_space : image_spaces) {
	mirror::Object* root = image_space->GetImageHeader().GetImageRoot(ImageHeader::kDexCaches);
	mirror::ObjectArray<mirror::DexCache>* dex_caches = root->AsObjectArray<mirror::DexCache>();
	for (int32_t i = 0; i < dex_caches->GetLength(); ++i) {
	mirror::DexCache* dex_cache = dex_caches->Get(i);
	const DexFile* dex_file = dex_cache->GetDexFile();
	// Binary search the dex file for the string index.
	const DexFile::StringId* string_id = dex_file->FindStringId(utf8.c_str());
	if (string_id != nullptr) {
	uint32_t string_idx = dex_file->GetIndexForStringId(*string_id);
	// GetResolvedString() contains a RB.
	mirror::String* image_string = dex_cache->GetResolvedString(string_idx);
	if (image_string != nullptr) {
	return image_string;
	}
	}
	}
	}
	return nullptr;
	}

	void InternTable::BroadcastForNewInterns() {
	CHECK(kUseReadBarrier);
	Thread* self = Thread::Current();
	MutexLock mu(self, *Locks::intern_table_lock_);
	weak_intern_condition_.Broadcast(self);
	}

	void InternTable::WaitUntilAccessible(Thread* self) {
	Locks::intern_table_lock_->ExclusiveUnlock(self);
	{
	ScopedThreadSuspension sts(self, kWaitingWeakGcRootRead);
	MutexLock mu(self, *Locks::intern_table_lock_);
	while (weak_root_state_ == gc::kWeakRootStateNoReadsOrWrites) {
	weak_intern_condition_.Wait(self);
	}
	}
	Locks::intern_table_lock_->ExclusiveLock(self);
	}

	mirror::String* InternTable::Insert(mirror::String* s, bool is_strong, bool holding_locks) {
	if (s == nullptr) {
	return nullptr;
	}
	Thread* const self = Thread::Current();
	MutexLock mu(self, *Locks::intern_table_lock_);
	if (kDebugLocking && !holding_locks) {
	Locks::mutator_lock_->AssertSharedHeld(self);
	CHECK_EQ(2u, self->NumberOfHeldMutexes()) << "may only safely hold the mutator lock";
	}
	while (true) {
	if (holding_locks) {
	if (!kUseReadBarrier) {
	CHECK_EQ(weak_root_state_, gc::kWeakRootStateNormal);
	} else {
	CHECK(self->GetWeakRefAccessEnabled());
	}
	}
	// Check the strong table for a match.
	mirror::String* strong = LookupStrong(s);
	if (strong != nullptr) {
	return strong;
	}
	if ((!kUseReadBarrier && weak_root_state_ != gc::kWeakRootStateNoReadsOrWrites) \|\|
	(kUseReadBarrier && self->GetWeakRefAccessEnabled())) {
	break;
	}
	// weak_root_state_ is set to gc::kWeakRootStateNoReadsOrWrites in the GC pause but is only
	// cleared after SweepSystemWeaks has completed. This is why we need to wait until it is
	// cleared.
	CHECK(!holding_locks);
	StackHandleScope<1> hs(self);
	auto h = hs.NewHandleWrapper(&s);
	WaitUntilAccessible(self);
	}
	if (!kUseReadBarrier) {
	CHECK_EQ(weak_root_state_, gc::kWeakRootStateNormal);
	} else {
	CHECK(self->GetWeakRefAccessEnabled());
	}
	// There is no match in the strong table, check the weak table.
	mirror::String* weak = LookupWeak(s);
	if (weak != nullptr) {
	if (is_strong) {
	// A match was found in the weak table. Promote to the strong table.
	RemoveWeak(weak);
	return InsertStrong(weak);
	}
	return weak;
	}
	// Check the image for a match.
	if (!images_added_to_intern_table_) {
	mirror::String* const image_string = LookupStringFromImage(s);
	if (image_string != nullptr) {
	return is_strong ? InsertStrong(image_string) : InsertWeak(image_string);
	}
	}
	// No match in the strong table or the weak table. Insert into the strong / weak table.
	return is_strong ? InsertStrong(s) : InsertWeak(s);
	}

	mirror::String* InternTable::InternStrong(int32_t utf16_length, const char* utf8_data) {
	DCHECK(utf8_data != nullptr);
	return InternStrong(mirror::String::AllocFromModifiedUtf8(
	Thread::Current(), utf16_length, utf8_data));
	}

	mirror::String* InternTable::InternStrong(const char* utf8_data) {
	DCHECK(utf8_data != nullptr);
	return InternStrong(mirror::String::AllocFromModifiedUtf8(Thread::Current(), utf8_data));
	}

	mirror::String* InternTable::InternStrongImageString(mirror::String* s) {
	// May be holding the heap bitmap lock.
	return Insert(s, true, true);
	}

	mirror::String* InternTable::InternStrong(mirror::String* s) {
	return Insert(s, true, false);
	}

	mirror::String* InternTable::InternWeak(mirror::String* s) {
	return Insert(s, false, false);
	}

	bool InternTable::ContainsWeak(mirror::String* s) {
	MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
	return LookupWeak(s) == s;
	}

	void InternTable::SweepInternTableWeaks(IsMarkedVisitor* visitor) {
	MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
	weak_interns_.SweepWeaks(visitor);
	}

	size_t InternTable::AddTableFromMemory(const uint8_t* ptr) {
	MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
	return AddTableFromMemoryLocked(ptr);
	}

	size_t InternTable::AddTableFromMemoryLocked(const uint8_t* ptr) {
	return strong_interns_.AddTableFromMemory(ptr);
	}

	size_t InternTable::WriteToMemory(uint8_t* ptr) {
	MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
	return strong_interns_.WriteToMemory(ptr);
	}

	std::size_t InternTable::StringHashEquals::operator()(const GcRoot<mirror::String>& root) const {
	if (kIsDebugBuild) {
	Locks::mutator_lock_->AssertSharedHeld(Thread::Current());
	}
	return static_cast<size_t>(root.Read()->GetHashCode());
	}

	bool InternTable::StringHashEquals::operator()(const GcRoot<mirror::String>& a,
	const GcRoot<mirror::String>& b) const {
	if (kIsDebugBuild) {
	Locks::mutator_lock_->AssertSharedHeld(Thread::Current());
	}
	return a.Read()->Equals(b.Read());
	}

	size_t InternTable::Table::AddTableFromMemory(const uint8_t* ptr) {
	size_t read_count = 0;
	UnorderedSet set(ptr, /make copy/false, &read_count);
	// TODO: Disable this for app images if app images have intern tables.
	static constexpr bool kCheckDuplicates = true;
	if (kCheckDuplicates) {
	for (GcRoot<mirror::String>& string : set) {
	CHECK(Find(string.Read()) == nullptr) << "Already found " << string.Read()->ToModifiedUtf8();
	}
	}
	// Insert at the front since we insert into the back.
	tables_.insert(tables_.begin(), std::move(set));
	return read_count;
	}

	size_t InternTable::Table::WriteToMemory(uint8_t* ptr) {
	if (tables_.empty()) {
	return 0;
	}
	UnorderedSet* table_to_write;
	UnorderedSet combined;
	if (tables_.size() > 1) {
	table_to_write = &combined;
	for (UnorderedSet& table : tables_) {
	for (GcRoot<mirror::String>& string : table) {
	combined.Insert(string);
	}
	}
	} else {
	table_to_write = &tables_.back();
	}
	return table_to_write->WriteToMemory(ptr);
	}

	void InternTable::Table::Remove(mirror::String* s) {
	for (UnorderedSet& table : tables_) {
	auto it = table.Find(GcRoot<mirror::String>(s));
	if (it != table.end()) {
	table.Erase(it);
	return;
	}
	}
	LOG(FATAL) << "Attempting to remove non-interned string " << s->ToModifiedUtf8();
	}

	mirror::String* InternTable::Table::Find(mirror::String* s) {
	Locks::intern_table_lock_->AssertHeld(Thread::Current());
	for (UnorderedSet& table : tables_) {
	auto it = table.Find(GcRoot<mirror::String>(s));
	if (it != table.end()) {
	return it->Read();
	}
	}
	return nullptr;
	}

	void InternTable::Table::AddNewTable() {
	tables_.push_back(UnorderedSet());
	}

	void InternTable::Table::Insert(mirror::String* s) {
	// Always insert the last table, the image tables are before and we avoid inserting into these
	// to prevent dirty pages.
	DCHECK(!tables_.empty());
	tables_.back().Insert(GcRoot<mirror::String>(s));
	}

	void InternTable::Table::VisitRoots(RootVisitor* visitor) {
	BufferedRootVisitor<kDefaultBufferedRootCount> buffered_visitor(
	visitor, RootInfo(kRootInternedString));
	for (UnorderedSet& table : tables_) {
	for (auto& intern : table) {
	buffered_visitor.VisitRoot(intern);
	}
	}
	}

	void InternTable::Table::SweepWeaks(IsMarkedVisitor* visitor) {
	for (UnorderedSet& table : tables_) {
	SweepWeaks(&table, visitor);
	}
	}

	void InternTable::Table::SweepWeaks(UnorderedSet* set, IsMarkedVisitor* visitor) {
	for (auto it = set->begin(), end = set->end(); it != end;) {
	// This does not need a read barrier because this is called by GC.
	mirror::Object* object = it->Read<kWithoutReadBarrier>();
	mirror::Object* new_object = visitor->IsMarked(object);
	if (new_object == nullptr) {
	it = set->Erase(it);
	} else {
	*it = GcRoot<mirror::String>(new_object->AsString());
	++it;
	}
	}
	}

	size_t InternTable::Table::Size() const {
	return std::accumulate(tables_.begin(),
	tables_.end(),
	0U,
	[](size_t sum, const UnorderedSet& set) {
	return sum + set.Size();
	});
	}

	void InternTable::ChangeWeakRootState(gc::WeakRootState new_state) {
	MutexLock mu(Thread::Current(), *Locks::intern_table_lock_);
	ChangeWeakRootStateLocked(new_state);
	}

	void InternTable::ChangeWeakRootStateLocked(gc::WeakRootState new_state) {
	CHECK(!kUseReadBarrier);
	weak_root_state_ = new_state;
	if (new_state != gc::kWeakRootStateNoReadsOrWrites) {
	weak_intern_condition_.Broadcast(Thread::Current());
	}
	}

	InternTable::Table::Table() {
	Runtime* const runtime = Runtime::Current();
	// Initial table.
	tables_.push_back(UnorderedSet());
	tables_.back().SetLoadFactor(runtime->GetHashTableMinLoadFactor(),
	runtime->GetHashTableMaxLoadFactor());
	}

	} // namespace art