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_