sync: Gracefully handle very early shutdown

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 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.
 class SYNC_EXPORT_PRIVATE Syncer {
  public:
   typedef std::vector<int64> UnsyncedMetaHandles;
 
-  Syncer();
+  Syncer(CancelationSignal* cancelation_signal);
   virtual ~Syncer();
 
-  // Called by other threads to tell the syncer to stop what it's doing
-  // and return early from SyncShare, if possible.
   bool ExitRequested();
-  void RequestEarlyExit();
 
   // Fetches and applies updates, resolves conflicts and commits local changes
   // for |request_types| as necessary until client and server states are in
   // sync.  The |nudge_tracker| contains state that describes why the client is
   // out of sync and what must be done to bring it back into sync.
   virtual bool NormalSyncShare(ModelTypeSet request_types,
                                const sessions::NudgeTracker& nudge_tracker,
                                sessions::SyncSession* session);
 
   // Performs an initial download for the |request_types|.  It is assumed that
@@ skipping 17 matching lines @@
   void ApplyUpdates(sessions::SyncSession* session);
   bool DownloadAndApplyUpdates(
       sessions::SyncSession* session,
       base::Callback<void(sync_pb::ClientToServerMessage*)> build_fn);
 
   void HandleCycleBegin(sessions::SyncSession* session);
   bool HandleCycleEnd(
       sessions::SyncSession* session,
       sync_pb::GetUpdatesCallerInfo::GetUpdatesSource source);
 
-  bool early_exit_requested_;
-  base::Lock early_exit_requested_lock_;
+  syncer::CancelationSignal* const cancelation_signal_;
 
   friend class SyncerTest;
   FRIEND_TEST_ALL_PREFIXES(SyncerTest, NameClashWithResolver);
   FRIEND_TEST_ALL_PREFIXES(SyncerTest, IllegalAndLegalUpdates);
   FRIEND_TEST_ALL_PREFIXES(SyncerTest, TestCommitListOrderingAndNewParent);
   FRIEND_TEST_ALL_PREFIXES(SyncerTest,
                            TestCommitListOrderingAndNewParentAndChild);
   FRIEND_TEST_ALL_PREFIXES(SyncerTest, TestCommitListOrderingCounterexample);
   FRIEND_TEST_ALL_PREFIXES(SyncerTest, TestCommitListOrderingWithNesting);
   FRIEND_TEST_ALL_PREFIXES(SyncerTest, TestCommitListOrderingWithNewItems);
   FRIEND_TEST_ALL_PREFIXES(SyncerTest, TestGetUnsyncedAndSimpleCommit);
   FRIEND_TEST_ALL_PREFIXES(SyncerTest, TestPurgeWhileUnsynced);
   FRIEND_TEST_ALL_PREFIXES(SyncerTest, TestPurgeWhileUnapplied);
   FRIEND_TEST_ALL_PREFIXES(SyncerTest, UnappliedUpdateDuringCommit);
   FRIEND_TEST_ALL_PREFIXES(SyncerTest, DeletingEntryInFolder);
   FRIEND_TEST_ALL_PREFIXES(SyncerTest,
                            LongChangelistCreatesFakeOrphanedEntries);
   FRIEND_TEST_ALL_PREFIXES(SyncerTest, QuicklyMergeDualCreatedHierarchy);
   FRIEND_TEST_ALL_PREFIXES(SyncerTest, LongChangelistWithApplicationConflict);
   FRIEND_TEST_ALL_PREFIXES(SyncerTest, DeletingEntryWithLocalEdits);
   FRIEND_TEST_ALL_PREFIXES(EntryCreatedInNewFolderTest,
                            EntryCreatedInNewFolderMidSync);
 
   DISALLOW_COPY_AND_ASSIGN(Syncer);
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_ENGINE_SYNCER_H_