sync: Per-type update application

sync/sessions/status_controller.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.
 
 // StatusController handles all counter and status related number crunching and
 // state tracking on behalf of a SyncSession.
 //
-// The most important feature of StatusController is the
-// ScopedModelSafeGroupRestriction.  Some of its functions expose per-thread
-// state, and can be called only when the restriction is in effect.  For
-// example, if GROUP_UI is set then the value returned from
-// commit_id_projection() will be useful for iterating over the commit IDs of
-// items that live on the UI thread.
-//
-// Other parts of its state are global, and do not require the restriction.
-//
-// NOTE: There is no concurrent access protection provided by this class. It
-// assumes one single thread is accessing this class for each unique
-// ModelSafeGroup, and also only one single thread (in practice, the
-// SyncerThread) responsible for all "shared" access when no restriction is in
-// place. Thus, every bit of data is to be accessed mutually exclusively with
-// respect to threads.
-//
-// StatusController can also track if changes occur to certain parts of state
-// so that various parts of the sync engine can avoid broadcasting
-// notifications if no changes occurred.
+// This object may be accessed from many different threads.  It will be accessed
+// most often from the syncer thread.  However, when update application is in
+// progress it may also be accessed from the worker threads.  This is safe
+// because only one of them will run at a time, and the syncer thread will be
+// blocked until update application completes.

[Nicolas Zea, 2013/11/19 22:45:26]

Does the status controller only hold model neutral information now? Perhaps
mention that no datatype specific state is being tracked?

[rlarocque, 2013/11/21 18:28:47]

It hasn't tracked any data type specific state for a while now.  I've added that
fact to the file comment.

In case you're wondering, yes, this does mean that we could merge
ModelNeutralState into this class.  But it gets complicated because the
ModelNeutralState is copied directly into the snapshot, while other counters,
like num encryption conflicts, are copied one at a time.  We'd need to refactor
the code so its definition isn't required all over the place before we can
remove it.

 
 #ifndef SYNC_SESSIONS_STATUS_CONTROLLER_H_
 #define SYNC_SESSIONS_STATUS_CONTROLLER_H_
 
 #include <map>
 #include <vector>
 
 #include "base/logging.h"
 #include "base/stl_util.h"
 #include "base/time/time.h"
@@ skipping 52 matching lines @@
   }
 
   // Returns true if the last updates response indicated that we were fully
   // up to date.  This is subtle: if it's false, it could either mean that
   // the server said there WAS more to download, or it could mean that we
   // were unable to reach the server.  If we didn't request every enabled
   // datatype, then we can't say for sure that there's nothing left to
   // download: in that case, this also returns false.
   bool ServerSaysNothingMoreToDownload() const;
 
-  ModelSafeGroup group_restriction() const {
-    return group_restriction_;
-  }
-
   base::Time sync_start_time() const {
     // The time at which we sent the first GetUpdates command for this sync.
     return sync_start_time_;
   }
 
   const ModelNeutralState& model_neutral_state() const {
     return model_neutral_;
   }
 
   SyncerError last_get_key_result() const;
@@ skipping 26 matching lines @@
   // A very important flag used to inform frontend of need to migrate.
   void set_types_needing_local_migration(ModelTypeSet types);
 
   void UpdateStartTime();
 
   void set_debug_info_sent();
 
   bool debug_info_sent() const;
 
  private:
-  friend class ScopedModelSafeGroupRestriction;
-
   ModelNeutralState model_neutral_;
 
-  // Used to fail read/write operations on state that don't obey the current
-  // active ModelSafeWorker contract.
-  bool group_restriction_in_effect_;
-  ModelSafeGroup group_restriction_;
-
   base::Time sync_start_time_;
 
   DISALLOW_COPY_AND_ASSIGN(StatusController);
 };
 
-// A utility to restrict access to only those parts of the given
-// StatusController that pertain to the specified ModelSafeGroup.
-class ScopedModelSafeGroupRestriction {
- public:
-  ScopedModelSafeGroupRestriction(StatusController* to_restrict,
-                                  ModelSafeGroup restriction)
-      : status_(to_restrict) {
-    DCHECK(!status_->group_restriction_in_effect_);
-    status_->group_restriction_ = restriction;
-    status_->group_restriction_in_effect_ = true;
-  }
-  ~ScopedModelSafeGroupRestriction() {
-    DCHECK(status_->group_restriction_in_effect_);
-    status_->group_restriction_in_effect_ = false;
-  }
- private:
-  StatusController* status_;
-  DISALLOW_COPY_AND_ASSIGN(ScopedModelSafeGroupRestriction);
-};
-
 }  // namespace sessions
 }  // namespace syncer
 
 #endif  // SYNC_SESSIONS_STATUS_CONTROLLER_H_