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
11namespace browser_sync {
12namespace sessions {
13class 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.
26class ModelChangingSyncerCommand : public SyncerCommand {
27 public:
28  ModelChangingSyncerCommand() : work_session_(NULL) { }
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
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