sync: Per-type update application

sync/engine/syncer.h

 // Copyright (c) 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_SYNCER_H_
 #define SYNC_ENGINE_SYNCER_H_
 
 #include <utility>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "base/gtest_prod_util.h"
 #include "base/synchronization/lock.h"
 #include "sync/base/sync_export.h"
 #include "sync/engine/conflict_resolver.h"
 #include "sync/engine/syncer_types.h"
 #include "sync/internal_api/public/base/model_type.h"
 #include "sync/sessions/sync_session.h"
 #include "sync/util/extensions_activity.h"
 
 namespace syncer {
 
 class CancelationSignal;
 
-// A Syncer provides a control interface for driving the individual steps
-// of the sync cycle.  Each cycle (hopefully) moves the client into closer
-// synchronization with the server.  The individual steps are modeled
-// as SyncerCommands, and the ordering of the steps is expressed using
-// the SyncerStep enum.
+// A Syncer provides a control interface for driving the sync cycle.  These
+// cycles consist of downloading updates, parsing the response (aka. process
+// updates), applying updates while resolving conflicts, and committing local
+// changes.  Some of these steps may be skipped if they're deemed to be
+// unnecessary.
 //
-// A Syncer instance expects to run on a dedicated thread.  Calls
-// to SyncShare() may take an unbounded amount of time, as SyncerCommands
-// may block on network i/o, on lock contention, or on tasks posted to
-// other threads.
+// A Syncer instance expects to run on a dedicated thread.  Calls to SyncShare()
+// may take an unbounded amount of time because it may block on network I/O, on
+// lock contention, or on tasks posted to other threads.
 class SYNC_EXPORT_PRIVATE Syncer {
  public:
   typedef std::vector<int64> UnsyncedMetaHandles;
 
   Syncer(CancelationSignal* cancelation_signal);
   virtual ~Syncer();
 
   bool ExitRequested();
 
   // Fetches and applies updates, resolves conflicts and commits local changes
@@ skipping 64 matching lines @@
   FRIEND_TEST_ALL_PREFIXES(SyncerTest, DeletingEntryWithLocalEdits);
   FRIEND_TEST_ALL_PREFIXES(EntryCreatedInNewFolderTest,
                            EntryCreatedInNewFolderMidSync);
 
   DISALLOW_COPY_AND_ASSIGN(Syncer);
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_ENGINE_SYNCER_H_