model_changing_syncer_command.h revision c407dc5cd9bdc5668497f21b26b09d988ab439de 
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
8#include "chrome/browser/sync/engine/syncer_command.h"
9
10namespace browser_sync {
11namespace sessions {
12class SyncSession;
13}
14
15// An abstract SyncerCommand which dispatches its Execute step to the
16// model-safe worker thread.  Classes derived from ModelChangingSyncerCommand
17// instead of SyncerCommand must implement ModelChangingExecuteImpl instead of
18// ExecuteImpl, but otherwise, the contract is the same.
19//
20// A command should derive from ModelChangingSyncerCommand instead of
21// SyncerCommand whenever the operation might change any client-visible
22// fields on any syncable::Entry.  If the operation involves creating a
23// WriteTransaction, this is a sign that ModelChangingSyncerCommand is likely
24// necessary.
25class ModelChangingSyncerCommand : public SyncerCommand {
26 public:
27  ModelChangingSyncerCommand() : work_session_(NULL) { }
28  virtual ~ModelChangingSyncerCommand() { }
29
30  // SyncerCommand implementation. Sets work_session to session.
31  virtual void ExecuteImpl(sessions::SyncSession* session);
32
33  // wrapper so implementations don't worry about storing work_session
34  void StartChangingModel() {
35    ModelChangingExecuteImpl(work_session_);
36  }
37
38  // Sometimes, a command has work to do that needs to touch global state
39  // belonging to multiple ModelSafeGroups, but in a way that is known to be
40  // safe.  This will be called once, prior to ModelChangingExecuteImpl,
41  // *without* a ModelSafeGroup restriction in place on the SyncSession.
42  // Returns true on success, false on failure.
43  // TODO(tim): Remove this (bug 36594).
44  virtual bool ModelNeutralExecuteImpl(sessions::SyncSession* session) {
45    return true;
46  }
47
48  // Abstract method to be implemented by subclasses to handle logic that
49  // operates on the model.  This is invoked with a SyncSession ModelSafeGroup
50  // restriction in place so that bits of state belonging to data types
51  // running on an unsafe thread are siloed away.
52  virtual void ModelChangingExecuteImpl(sessions::SyncSession* session) = 0;
53
54 private:
55  // ExecuteImpl is expected to be run by SyncerCommand to set work_session.
56  // StartChangingModel is called to start this command running.
57  // Implementations will implement ModelChangingExecuteImpl and not
58  // worry about storing the session or setting it. They are given work_session.
59  sessions::SyncSession* work_session_;
60
61  DISALLOW_COPY_AND_ASSIGN(ModelChangingSyncerCommand);
62};
63
64}  // namespace browser_sync
65
66#endif  // CHROME_BROWSER_SYNC_ENGINE_MODEL_CHANGING_SYNCER_COMMAND_H_
67