sync: Per-type update application

sync/engine/model_changing_syncer_command.h

-// Copyright 2012 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 SYNC_ENGINE_MODEL_CHANGING_SYNCER_COMMAND_H_
-#define SYNC_ENGINE_MODEL_CHANGING_SYNCER_COMMAND_H_
-
-#include "base/compiler_specific.h"
-#include "sync/base/sync_export.h"
-#include "sync/engine/syncer_command.h"
-#include "sync/internal_api/public/engine/model_safe_worker.h"
-
-namespace syncer {
-namespace sessions {
-class SyncSession;
-}
-
-// 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 SYNC_EXPORT_PRIVATE ModelChangingSyncerCommand : public SyncerCommand {
- public:
-  ModelChangingSyncerCommand() : work_session_(NULL) { }
-  virtual ~ModelChangingSyncerCommand() { }
-
-  // SyncerCommand implementation. Sets work_session to session.
-  virtual SyncerError ExecuteImpl(sessions::SyncSession* session) OVERRIDE;
-
-  // Wrapper so implementations don't worry about storing work_session.
-  SyncerError StartChangingModel() {
-    return ModelChangingExecuteImpl(work_session_);
-  }
-
-  std::set<ModelSafeGroup> GetGroupsToChangeForTest(
-      const sessions::SyncSession& session) const {
-    return GetGroupsToChange(session);
-  }
-
- protected:
-  // This should return the set of groups in |session| that need to be
-  // changed.  The returned set should be a subset of
-  // session.GetEnabledGroups().  Subclasses can guarantee this either
-  // by calling one of the session.GetEnabledGroups*() functions and
-  // filtering that, or using GetGroupForModelType() (which handles
-  // top-level/unspecified nodes) to project from model types to
-  // groups.
-  virtual std::set<ModelSafeGroup> GetGroupsToChange(
-      const sessions::SyncSession& session) const = 0;
-
-  // Abstract method to be implemented by subclasses to handle logic that
-  // operates on the model.  This is invoked with a SyncSession ModelSafeGroup
-  // restriction in place so that bits of state belonging to data types
-  // running on an unsafe thread are siloed away.
-  virtual SyncerError ModelChangingExecuteImpl(
-      sessions::SyncSession* 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.
-  sessions::SyncSession* work_session_;
-
-  DISALLOW_COPY_AND_ASSIGN(ModelChangingSyncerCommand);
-};
-
-}  // namespace syncer
-
-#endif  // SYNC_ENGINE_MODEL_CHANGING_SYNCER_COMMAND_H_