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1 // Copyright (c) 2006-2009 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #ifndef CHROME_BROWSER_SYNC_ENGINE_MODEL_CHANGING_SYNCER_COMMAND_H_
6 #define CHROME_BROWSER_SYNC_ENGINE_MODEL_CHANGING_SYNCER_COMMAND_H_
7 #pragma once
8 
9 #include "chrome/browser/sync/engine/syncer_command.h"
10 
11 namespace browser_sync {
12 namespace sessions {
13 class SyncSession;
14 }
15 
16 // An abstract SyncerCommand which dispatches its Execute step to the
17 // model-safe worker thread.  Classes derived from ModelChangingSyncerCommand
18 // instead of SyncerCommand must implement ModelChangingExecuteImpl instead of
19 // ExecuteImpl, but otherwise, the contract is the same.
20 //
21 // A command should derive from ModelChangingSyncerCommand instead of
22 // SyncerCommand whenever the operation might change any client-visible
23 // fields on any syncable::Entry.  If the operation involves creating a
24 // WriteTransaction, this is a sign that ModelChangingSyncerCommand is likely
25 // necessary.
26 class ModelChangingSyncerCommand : public SyncerCommand {
27  public:
ModelChangingSyncerCommand()28   ModelChangingSyncerCommand() : work_session_(NULL) { }
~ModelChangingSyncerCommand()29   virtual ~ModelChangingSyncerCommand() { }
30 
31   // SyncerCommand implementation. Sets work_session to session.
32   virtual void ExecuteImpl(sessions::SyncSession* session);
33 
34   // wrapper so implementations don't worry about storing work_session
StartChangingModel()35   void StartChangingModel() {
36     ModelChangingExecuteImpl(work_session_);
37   }
38 
39   // Sometimes, a command has work to do that needs to touch global state
40   // belonging to multiple ModelSafeGroups, but in a way that is known to be
41   // safe.  This will be called once, prior to ModelChangingExecuteImpl,
42   // *without* a ModelSafeGroup restriction in place on the SyncSession.
43   // Returns true on success, false on failure.
44   // TODO(tim): Remove this (bug 36594).
45   virtual bool ModelNeutralExecuteImpl(sessions::SyncSession* session);
46 
47   // Abstract method to be implemented by subclasses to handle logic that
48   // operates on the model.  This is invoked with a SyncSession ModelSafeGroup
49   // restriction in place so that bits of state belonging to data types
50   // running on an unsafe thread are siloed away.
51   virtual void ModelChangingExecuteImpl(sessions::SyncSession* session) = 0;
52 
53  private:
54   // ExecuteImpl is expected to be run by SyncerCommand to set work_session.
55   // StartChangingModel is called to start this command running.
56   // Implementations will implement ModelChangingExecuteImpl and not
57   // worry about storing the session or setting it. They are given work_session.
58   sessions::SyncSession* work_session_;
59 
60   DISALLOW_COPY_AND_ASSIGN(ModelChangingSyncerCommand);
61 };
62 
63 }  // namespace browser_sync
64 
65 #endif  // CHROME_BROWSER_SYNC_ENGINE_MODEL_CHANGING_SYNCER_COMMAND_H_
66