[IndexedDB] Pool and evict leveldb iterators, to save memory

content/browser/indexed_db/leveldb/leveldb_database.h

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_INDEXED_DB_LEVELDB_LEVELDB_DATABASE_H_
 #define CONTENT_BROWSER_INDEXED_DB_LEVELDB_LEVELDB_DATABASE_H_
 
 #include <memory>
 #include <string>
 
+#include "base/containers/mru_cache.h"
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/strings/string16.h"
 #include "base/strings/string_piece.h"
 #include "base/trace_event/memory_dump_provider.h"
 #include "content/common/content_export.h"
 #include "third_party/leveldatabase/src/include/leveldb/comparator.h"
 #include "third_party/leveldatabase/src/include/leveldb/status.h"
 
 namespace leveldb {
@@ skipping 47 matching lines @@
     const char* Name() const override;
 
     void FindShortestSeparator(std::string* start,
                                const leveldb::Slice& limit) const override;
     void FindShortSuccessor(std::string* key) const override;
 
    private:
     const LevelDBComparator* comparator_;
   };
 
+  static leveldb::Status OpenForTesting(const base::FilePath& file_name,
+                                        const LevelDBComparator* comparator,
+                                        std::unique_ptr<LevelDBDatabase>* db,
+                                        size_t max_open_cursors);
+
   static leveldb::Status Open(const base::FilePath& file_name,
                               const LevelDBComparator* comparator,
                               std::unique_ptr<LevelDBDatabase>* db,
                               bool* is_disk_full = 0);
   static std::unique_ptr<LevelDBDatabase> OpenInMemory(
       const LevelDBComparator* comparator);
   static leveldb::Status Destroy(const base::FilePath& file_name);
   static std::unique_ptr<LevelDBLock> LockForTesting(
       const base::FilePath& file_name);
   ~LevelDBDatabase() override;
 
   leveldb::Status Put(const base::StringPiece& key, std::string* value);
   leveldb::Status Remove(const base::StringPiece& key);
   virtual leveldb::Status Get(const base::StringPiece& key,
                               std::string* value,
                               bool* found,
                               const LevelDBSnapshot* = 0);
   leveldb::Status Write(const LevelDBWriteBatch& write_batch);
   std::unique_ptr<LevelDBIterator> CreateIterator(const LevelDBSnapshot* = 0);
   const LevelDBComparator* Comparator() const;
   void Compact(const base::StringPiece& start, const base::StringPiece& stop);
   void CompactAll();
 
   // base::trace_event::MemoryDumpProvider implementation.
   bool OnMemoryDump(const base::trace_event::MemoryDumpArgs& args,
                     base::trace_event::ProcessMemoryDump* pmd) override;
 
+  void NotifyIteratorCreated(LevelDBIterator*);
+  void NotifyIteratorUsed(LevelDBIterator*);
+  void NotifyIteratorDestroyed(LevelDBIterator*);
+
  protected:
   LevelDBDatabase();
+  LevelDBDatabase(size_t max_open_iterators);
 
  private:
   friend class LevelDBSnapshot;
 
   void CloseDatabase();
 
   std::unique_ptr<leveldb::Env> env_;
   std::unique_ptr<leveldb::Comparator> comparator_adapter_;
   std::unique_ptr<leveldb::DB> db_;
   std::unique_ptr<const leveldb::FilterPolicy> filter_policy_;
   const LevelDBComparator* comparator_;
+
+  // Despite the type name, this object uses LRU eviction.
+  base::MRUCache<LevelDBIterator*, LevelDBIterator*> iterator_lru_;
+  // Recorded for UMA reporting.
+  uint32_t num_iterators_ = 0;
+  uint32_t max_iterators_ = 0;
+
   std::string file_name_for_tracing;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_INDEXED_DB_LEVELDB_LEVELDB_DATABASE_H_