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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:
     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