sync/engine/model_changing_syncer_command.h

   1 // Copyright 2012 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 SYNC_ENGINE_MODEL_CHANGING_SYNCER_COMMAND_H_
   6 #define SYNC_ENGINE_MODEL_CHANGING_SYNCER_COMMAND_H_
   7
   8 #include "base/compiler_specific.h"
   9 #include "sync/base/sync_export.h"
  10 #include "sync/engine/syncer_command.h"
  11 #include "sync/internal_api/public/engine/model_safe_worker.h"
  12
  13 namespace syncer {
  14 namespace sessions {
  15 class SyncSession;
  16 }
  17
  18 // An abstract SyncerCommand which dispatches its Execute step to the
  19 // model-safe worker thread.  Classes derived from ModelChangingSyncerCommand
  20 // instead of SyncerCommand must implement ModelChangingExecuteImpl instead of
  21 // ExecuteImpl, but otherwise, the contract is the same.
  22 //
  23 // A command should derive from ModelChangingSyncerCommand instead of
  24 // SyncerCommand whenever the operation might change any client-visible
  25 // fields on any syncable::Entry.  If the operation involves creating a
  26 // WriteTransaction, this is a sign that ModelChangingSyncerCommand is likely
  27 // necessary.
  28 class SYNC_EXPORT_PRIVATE ModelChangingSyncerCommand : public SyncerCommand {
  29  public:
  30   ModelChangingSyncerCommand() : work_session_(NULL) { }
  31   virtual ~ModelChangingSyncerCommand() { }
  32
  33   // SyncerCommand implementation. Sets work_session to session.
  34   virtual SyncerError ExecuteImpl(sessions::SyncSession* session) OVERRIDE;
  35
  36   // Wrapper so implementations don't worry about storing work_session.
  37   SyncerError StartChangingModel() {
  38     return ModelChangingExecuteImpl(work_session_);
  39   }
  40
  41   std::set<ModelSafeGroup> GetGroupsToChangeForTest(
  42       const sessions::SyncSession& session) const {
  43     return GetGroupsToChange(session);
  44   }
  45
  46  protected:
  47   // This should return the set of groups in |session| that need to be
  48   // changed.  The returned set should be a subset of
  49   // session.GetEnabledGroups().  Subclasses can guarantee this either
  50   // by calling one of the session.GetEnabledGroups*() functions and
  51   // filtering that, or using GetGroupForModelType() (which handles
  52   // top-level/unspecified nodes) to project from model types to
  53   // groups.
  54   virtual std::set<ModelSafeGroup> GetGroupsToChange(
  55       const sessions::SyncSession& session) const = 0;
  56
  57   // Abstract method to be implemented by subclasses to handle logic that
  58   // operates on the model.  This is invoked with a SyncSession ModelSafeGroup
  59   // restriction in place so that bits of state belonging to data types
  60   // running on an unsafe thread are siloed away.
  61   virtual SyncerError ModelChangingExecuteImpl(
  62       sessions::SyncSession* session) = 0;
  63
  64  private:
  65   // ExecuteImpl is expected to be run by SyncerCommand to set work_session.
  66   // StartChangingModel is called to start this command running.
  67   // Implementations will implement ModelChangingExecuteImpl and not
  68   // worry about storing the session or setting it. They are given work_session.
  69   sessions::SyncSession* work_session_;
  70
  71   DISALLOW_COPY_AND_ASSIGN(ModelChangingSyncerCommand);
  72 };
  73
  74 }  // namespace syncer
  75
  76 #endif  // SYNC_ENGINE_MODEL_CHANGING_SYNCER_COMMAND_H_