IndexedDB: Recycle cursor objects when calling continue().

content/browser/in_process_webkit/indexed_db_dispatcher_host.cc

 // Copyright (c) 2011 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.
 
 #include "content/browser/in_process_webkit/indexed_db_dispatcher_host.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/utf_string_conversions.h"
 #include "content/browser/browser_thread.h"
@@ skipping 933 matching lines @@
 void IndexedDBDispatcherHost::CursorDispatcherHost::OnContinue(
     int32 cursor_id,
     int32 response_id,
     const IndexedDBKey& key,
     WebKit::WebExceptionCode* ec) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::WEBKIT));
   WebIDBCursor* idb_cursor = parent_->GetOrTerminateProcess(&map_, cursor_id);
   if (!idb_cursor)
     return;
 
+  parent_->pending_cursor_continues_[response_id] = cursor_id;

[michaeln, 2011/10/30 21:54:06]

What if the continue call does not complete successfully? How is the map entry
removed in that case?

[michaeln, 2011/10/31 15:08:18]

Looks like there are two ways in which continue does not succeed...
- the method call below throws an exception by setting *ec to non-zero
- instead of onSuccessCursorContinue() eventually being called,
onSuccess(nullValue()) is called.

Instead of holding this extra state in a separate map entry, have you considered
stuffing the required state into the  IndexedDBCallbacks<WebIDBCursor> instance
so that it knows what cursor_id its dealing with and there are no extra map
entries to cleanup on any of the possible return path.

[hans, 2011/10/31 16:11:52]

Right, passing the cursor_id into the callbacks object solves this problem
nicely, so let's do that.

+
   *ec = 0;
   idb_cursor->continueFunction(
       key, new IndexedDBCallbacks<WebIDBCursor>(parent_, response_id), *ec);
 }
 
 void IndexedDBDispatcherHost::CursorDispatcherHost::OnDelete(
     int32 cursor_id,
     int32 response_id,
     WebKit::WebExceptionCode* ec) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::WEBKIT));
@@ skipping 102 matching lines @@
   }
   idb_transaction->didCompleteTaskEvents();
 }
 
 void IndexedDBDispatcherHost::TransactionDispatcherHost::OnDestroyed(
     int32 object_id) {
   transaction_size_map_.erase(object_id);
   transaction_url_map_.erase(object_id);
   parent_->DestroyObject(&map_, object_id);
 }