sync: GU retry with less explicit TimeTicks logic

sync/sessions/nudge_tracker.h

 // Copyright 2013 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.
 //
 // A class to track the outstanding work required to bring the client back into
 // sync with the server.
 #ifndef SYNC_SESSIONS_NUDGE_TRACKER_H_
 #define SYNC_SESSIONS_NUDGE_TRACKER_H_
 
 #include <list>
@@ skipping 18 matching lines @@
   NudgeTracker();
   ~NudgeTracker();
 
   // Returns true if there is a good reason for performing a sync cycle.
   // This does not take into account whether or not this is a good *time* to
   // perform a sync cycle; that's the scheduler's job.
   bool IsSyncRequired() const;
 
   // Returns true if there is a good reason for performing a get updates
   // request as part of the next sync cycle.
-  bool IsGetUpdatesRequired(base::TimeTicks now) const;
+  bool IsGetUpdatesRequired() const;
 
   // Return true if should perform a sync cycle for GU retry.
-  bool IsRetryRequired(base::TimeTicks now) const;
+  //
+  // This is sensitive to changes in 'current time'.  Its value can be affected
+  // by SetSyncCycleStartTime(), SetNextRetryTime(), and
+  // RecordSuccessfulSyncCycle().  Please refer to those functions for more
+  // information on how this flag is maintained.
+  bool IsRetryRequired() const;
 
   // Tells this class that all required update fetching or committing has
   // completed successfully.
-  void RecordSuccessfulSyncCycle(base::TimeTicks now);
+  void RecordSuccessfulSyncCycle();
 
   // Takes note of a local change.
   void RecordLocalChange(ModelTypeSet types);
 
   // Takes note of a locally issued request to refresh a data type.
   void RecordLocalRefreshRequest(ModelTypeSet types);
 
   // Takes note of the receipt of an invalidation notice from the server.
   void RecordRemoteInvalidation(
       const ObjectIdInvalidationMap& invalidation_map);
@@ skipping 41 matching lines @@
       ModelType type,
       sync_pb::GetUpdateTriggers* msg) const;
 
   // Fills a ProgressMarker with single legacy notification hint expected by the
   // sync server.  Newer servers will rely on the data set by FillProtoMessage()
   // instead of this.
   void SetLegacyNotificationHint(
       ModelType type,
       sync_pb::DataTypeProgressMarker* progress) const;
 
+  // Flips the flag if we're due for a retry.
+  void SetSyncCycleStartTime(base::TimeTicks now);
+
   // Adjusts the number of hints that can be stored locally.
   void SetHintBufferSize(size_t size);
 
-  void set_next_retry_time(base::TimeTicks next_retry_time) {
-    next_retry_time_ = next_retry_time;
-  }
+  // Schedules a retry GetUpdate request for some time in the future.
+  //
+  // This is a request sent to us as part of a server response requesting
+  // that the client perform a GetUpdate request at |next_retry_time| to
+  // fetch any updates it may have missed in the first attempt.
+  //
+  // To avoid strange results from IsRetryRequired() during a sync cycle, the
+  // effects of this change are not guaranteed to take effect until
+  // SetSyncCycleStartTime() is called at the start of the *next* sync cycle.
+  void SetNextRetryTime(base::TimeTicks next_retry_time);
 
  private:
   typedef std::map<ModelType, DataTypeTracker> TypeTrackerMap;
 
   TypeTrackerMap type_trackers_;
 
   // Merged updates source.  This should be obsolete, but the server still
   // relies on it for some heuristics.
   sync_pb::GetUpdatesCallerInfo::GetUpdatesSource updates_source_;
 
   // Tracks whether or not invalidations are currently enabled.
   bool invalidations_enabled_;
 
   // This flag is set if suspect that some technical malfunction or known bug
   // may have left us with some unserviced invalidations.
   //
   // Keeps track of whether or not we're fully in sync with the invalidation
   // server.  This can be false even if invalidations are enabled and working
   // correctly.  For example, until we get ack-tracking working properly, we
   // won't persist invalidations between restarts, so we may be out of sync when
   // we restart.  The only way to get back into sync is to have invalidations
   // enabled, then complete a sync cycle to make sure we're fully up to date.
   bool invalidations_out_of_sync_;
 
   size_t num_payloads_per_type_;
 
   base::TimeTicks last_successful_sync_time_;
 
-  // A retry GU should be issued after this time.
+  // A pending update to the current_retry_time_.
+  //
+  // The GU retry time is specified by a call to SetNextRetryTime, but we don't
+  // want that change to take effect right away, since it could happen in the
+  // middle of a sync cycle.  We delay the update until the start of the next
+  // sync cycle, which is indicated by a call to SetSyncCycleStartTime().
   base::TimeTicks next_retry_time_;
 
+  // The currently active retry GU time.  Will be null if there is no retry GU
+  // pending at this time.
+  base::TimeTicks current_retry_time_;
+
+  // The time when the sync cycle started.  This value is maintained by
+  // SetSyncCycleStartTime().  This may contain a stale value if we're not
+  // currently in a sync cycle.
+  base::TimeTicks sync_cycle_start_time_;
+
   DISALLOW_COPY_AND_ASSIGN(NudgeTracker);
 };
 
 }  // namespace sessions
 }  // namespace syncer
 
 #endif  // SYNC_SESSIONS_NUDGE_TRACKER_H_