Initial commit of sync engine code to browser/sync....

chrome/browser/sync/engine/model_changing_syncer_command.h

+// Copyright (c) 2006-2009 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.
+
+#ifndef CHROME_BROWSER_SYNC_ENGINE_MODEL_CHANGING_SYNCER_COMMAND_H_
+#define CHROME_BROWSER_SYNC_ENGINE_MODEL_CHANGING_SYNCER_COMMAND_H_
+
+#include "chrome/browser/sync/engine/syncer_command.h"
+
+namespace browser_sync {
+
+// An abstract SyncerCommand which dispatches its Execute step to the
+// model-safe worker thread.  Classes derived from ModelChangingSyncerCommand
+// instead of SyncerCommand must implement ModelChangingExecuteImpl instead of
+// ExecuteImpl, but otherwise, the contract is the same.
+//
+// A command should derive from ModelChangingSyncerCommand instead of
+// SyncerCommand whenever the operation might change any client-visible
+// fields on any syncable::Entry.  If the operation involves creating a
+// WriteTransaction, this is a sign that ModelChangingSyncerCommand is likely
+// necessary.
+class ModelChangingSyncerCommand : public SyncerCommand {
+ public:
+  ModelChangingSyncerCommand() : work_session_(NULL) { }
+  virtual ~ModelChangingSyncerCommand() { }
+
+  // SyncerCommand implementation. Sets work_session to session.
+  virtual void ExecuteImpl(SyncerSession* session);
+
+  // wrapper so implementations don't worry about storing work_session
+  void StartChangingModel() {
+    ModelChangingExecuteImpl(work_session_);
+  }
+
+  // Abstract method to be implemented by subclasses.
+  virtual void ModelChangingExecuteImpl(SyncerSession* session) = 0;
+
+ private:
+  // ExecuteImpl is expected to be run by SyncerCommand to set work_session.
+  // StartChangingModel is called to start this command running.
+  // Implementations will implement ModelChangingExecuteImpl and not
+  // worry about storing the session or setting it. They are given work_session.
+  SyncerSession* work_session_;
+
+  DISALLOW_COPY_AND_ASSIGN(ModelChangingSyncerCommand);
+};
+
+}  // namespace browser_sync
+
+#endif  // CHROME_BROWSER_SYNC_ENGINE_MODEL_CHANGING_SYNCER_COMMAND_H_