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

content/browser/indexed_db/leveldb/leveldb_iterator.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_ITERATOR_H_
 #define CONTENT_BROWSER_INDEXED_DB_LEVELDB_LEVELDB_ITERATOR_H_
 
 #include "base/strings/string_piece.h"
 #include "content/common/content_export.h"
 #include "third_party/leveldatabase/src/include/leveldb/status.h"
 
 namespace content {
 
 class CONTENT_EXPORT LevelDBIterator {
  public:
   virtual ~LevelDBIterator() {}
   virtual bool IsValid() const = 0;
   virtual leveldb::Status SeekToLast() = 0;
   virtual leveldb::Status Seek(const base::StringPiece& target) = 0;
   virtual leveldb::Status Next() = 0;
   virtual leveldb::Status Prev() = 0;
   virtual base::StringPiece Key() const = 0;
   virtual base::StringPiece Value() const = 0;
+
+  // Detaches the internal iterator which saves memory at the performance
+  // expense of reloading and seeking later if the iterator is needed again for
+  // |Seek*|, |Next|, |Prev|, or |Value|.
+  virtual void Detach(){};

[jsbell, 2017/03/27 15:35:34]

Nit: space between ) and {

Also, since we DCHECK if you call Detach() twice in the impl that should be
noted as part of the contract.

[dmurph, 2017/03/27 21:32:05]

ugh. Darn clang format! Actually, should I just keep it this way because it's
clang-formatted? It keeps reverting every time I run git cl format.

[pwnall, 2017/03/27 21:52:18]

I would suggest keeping the code as-is and and filing a bug.

+  virtual bool IsDetached() const;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_INDEXED_DB_LEVELDB_LEVELDB_ITERATOR_H_