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

content/browser/indexed_db/leveldb/leveldb_transaction.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_TRANSACTION_H_
 #define CONTENT_BROWSER_INDEXED_DB_LEVELDB_LEVELDB_TRANSACTION_H_
 
 #include <map>
 #include <memory>
 #include <set>
@@ skipping 75 matching lines @@
     static std::unique_ptr<DataIterator> Create(
         LevelDBTransaction* transaction);
     ~DataIterator() override;
     bool IsValid() const override;
     leveldb::Status SeekToLast() override;
     leveldb::Status Seek(const base::StringPiece& slice) override;
     leveldb::Status Next() override;
     leveldb::Status Prev() override;
     base::StringPiece Key() const override;
     base::StringPiece Value() const override;
+
     bool IsDeleted() const;
 
     // Mark the current record as deleted.
     void Delete();
 
    private:
     explicit DataIterator(LevelDBTransaction* transaction);
     DataType* data_;
     DataType::iterator iterator_;
 
@@ skipping 10 matching lines @@
     static std::unique_ptr<TransactionIterator> Create(
         scoped_refptr<LevelDBTransaction> transaction);
 
     bool IsValid() const override;
     leveldb::Status SeekToLast() override;
     leveldb::Status Seek(const base::StringPiece& target) override;
     leveldb::Status Next() override;
     leveldb::Status Prev() override;
     base::StringPiece Key() const override;
     base::StringPiece Value() const override;
+    void EvictWorkingMemory() override;
+
     void DataChanged();
 
     // Mark the current record as deleted. If an existing record
     // is present in the uncommitted data this will convert it to
     // a deletion record, otherwise it will insert a new one.
     void Delete();
 
    private:
     enum Direction { FORWARD, REVERSE };
 
     explicit TransactionIterator(scoped_refptr<LevelDBTransaction> transaction);
     void HandleConflictsAndDeletes();
     void SetCurrentIteratorToSmallestKey();
     void SetCurrentIteratorToLargestKey();
     void RefreshDataIterator() const;
     bool DataIteratorIsLower() const;
     bool DataIteratorIsHigher() const;
 
+    void LoadDBIteratorIfEvicted();
+
     scoped_refptr<LevelDBTransaction> transaction_;
     const LevelDBComparator* comparator_;
     mutable std::unique_ptr<DataIterator> data_iterator_;
     std::unique_ptr<LevelDBIterator> db_iterator_;
     LevelDBIterator* current_ = nullptr;
 
+    bool is_evicted_ = false;
+    std::string key_after_eviction_;
+
     Direction direction_ = FORWARD;
     mutable bool data_changed_ = false;
 
     DISALLOW_COPY_AND_ASSIGN(TransactionIterator);
   };
 
   void Set(const base::StringPiece& key, std::string* value, bool deleted);
   void RegisterIterator(TransactionIterator* iterator);
   void UnregisterIterator(TransactionIterator* iterator);
   void NotifyIterators();
@@ skipping 29 matching lines @@
   LevelDBDatabase* db_;
   std::unique_ptr<LevelDBWriteBatch> write_batch_;
   bool finished_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(LevelDBDirectTransaction);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_INDEXED_DB_LEVELDB_LEVELDB_TRANSACTION_H_