Do not observe MessageLoop destruction from ModelSafeWorker.

components/sync/engine/model_safe_worker.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.
 
 #ifndef COMPONENTS_SYNC_ENGINE_MODEL_SAFE_WORKER_H_
 #define COMPONENTS_SYNC_ENGINE_MODEL_SAFE_WORKER_H_
 
 #include <map>
 #include <memory>
 #include <string>
-#include <vector>
 
-#include "base/callback.h"
+#include "base/callback_forward.h"
+#include "base/macros.h"
 #include "base/memory/ref_counted.h"
-#include "base/message_loop/message_loop.h"
-#include "base/single_thread_task_runner.h"
-#include "base/synchronization/lock.h"
+#include "base/synchronization/atomic_flag.h"
 #include "components/sync/base/model_type.h"
 #include "components/sync/base/syncer_error.h"
 
 namespace base {
 class DictionaryValue;
 }  // namespace base
 
 namespace syncer {
 
 typedef base::Callback<enum SyncerError(void)> WorkCallback;
@@ skipping 11 matching lines @@
                        // being synced.  On windows and linux, this runs on the
                        // DB thread.
   GROUP_NON_BLOCKING,  // Models that correspond to non-blocking types. These
                        // models always stay in GROUP_NON_BLOCKING; changes are
                        // forwarded to these models without ModelSafeWorker/
                        // SyncBackendRegistrar involvement.
 };
 
 std::string ModelSafeGroupToString(ModelSafeGroup group);
 
-// WorkerLoopDestructionObserver is notified when the thread where it works
-// is going to be destroyed.
-class WorkerLoopDestructionObserver {
- public:
-  virtual void OnWorkerLoopDestroyed(ModelSafeGroup group) = 0;
-};
-
 // The Syncer uses a ModelSafeWorker for all tasks that could potentially
 // modify syncable entries (e.g under a WriteTransaction). The ModelSafeWorker
 // only knows how to do one thing, and that is take some work (in a fully
 // pre-bound callback) and have it performed (as in Run()) from a thread which
 // is guaranteed to be "model-safe", where "safe" refers to not allowing us to
 // cause an embedding application model to fall out of sync with the
 // syncable::Directory due to a race. Each ModelSafeWorker is affiliated with
-// a thread and does actual work on that thread. On the destruction of that
-// thread, the affiliated worker is effectively disabled to do more
-// work and will notify its observer.
-class ModelSafeWorker : public base::RefCountedThreadSafe<ModelSafeWorker>,
-                        public base::MessageLoop::DestructionObserver {
+// a thread and does actual work on that thread.
+class ModelSafeWorker : public base::RefCountedThreadSafe<ModelSafeWorker> {
  public:
-  // Subclass should implement to observe destruction of the loop where
-  // it actually does work. Called on UI thread immediately after worker is
-  // created.
-  virtual void RegisterForLoopDestruction() = 0;
-
-  // Called on sync loop from SyncBackendRegistrar::ShutDown(). Post task to
-  // working loop to stop observing loop destruction and invoke
-  // |unregister_done_callback|.
-  virtual void UnregisterForLoopDestruction(
-      base::Callback<void(ModelSafeGroup)> unregister_done_callback);
-
   // If not stopped, call DoWorkAndWaitUntilDoneImpl() to do work. Otherwise
   // return CANNOT_DO_WORK.
   SyncerError DoWorkAndWaitUntilDone(const WorkCallback& work);
 
   // Soft stop worker by setting stopped_ flag. Called when sync is disabled
   // or browser is shutting down. Called on UI loop.
   virtual void RequestStop();
 
   virtual ModelSafeGroup GetModelSafeGroup() = 0;
 
-  // MessageLoop::DestructionObserver implementation.
-  void WillDestroyCurrentMessageLoop() override;
-
  protected:
-  explicit ModelSafeWorker(WorkerLoopDestructionObserver* observer);
-  ~ModelSafeWorker() override;
+  ModelSafeWorker();
+  virtual ~ModelSafeWorker();
 
   // Any time the Syncer performs model modifications (e.g employing a
   // WriteTransaction), it should be done by this method to ensure it is done
   // from a model-safe thread.
   virtual SyncerError DoWorkAndWaitUntilDoneImpl(const WorkCallback& work) = 0;
 
   // Return true if the worker was stopped. Thread safe.
   bool IsStopped();
 
-  // Subclass should call this in RegisterForLoopDestruction() from the loop
-  // where work is done.
-  void SetWorkingLoopToCurrent();
-
  private:
   friend class base::RefCountedThreadSafe<ModelSafeWorker>;
 
-  void UnregisterForLoopDestructionAsync(
-      base::Callback<void(ModelSafeGroup)> unregister_done_callback);
+  // Whether the worker should do more work. Set when sync is disabled.
+  base::AtomicFlag stopped_;
 
-  // Whether the worker should/can do more work. Set when sync is disabled or
-  // when the worker's working thread is to be destroyed.
-  base::Lock stopped_lock_;
-  bool stopped_;
-
-  // Notified when working thread of the worker is to be destroyed.
-  WorkerLoopDestructionObserver* observer_;
-
-  // Remember working loop for posting task to unregister destruction
-  // observation from sync thread when shutting down sync.
-  base::Lock working_task_runner_lock_;
-  scoped_refptr<base::SingleThreadTaskRunner> working_task_runner_;
-
-  // Callback passed with UnregisterForLoopDestruction. Normally this
-  // remains unset/unused and is stored only if |working_task_runner_| isn't
-  // initialized by the time UnregisterForLoopDestruction is called.
-  // It is safe to copy and thread safe.
-  // See comments in model_safe_worker.cc for more details.
-  base::Callback<void(ModelSafeGroup)> unregister_done_callback_;
+  DISALLOW_COPY_AND_ASSIGN(ModelSafeWorker);
 };
 
 // A map that details which ModelSafeGroup each ModelType
 // belongs to.  Routing info can change in response to the user enabling /
 // disabling sync for certain types, as well as model association completions.
 typedef std::map<ModelType, ModelSafeGroup> ModelSafeRoutingInfo;
 
 // Caller takes ownership of return value.
 std::unique_ptr<base::DictionaryValue> ModelSafeRoutingInfoToValue(
     const ModelSafeRoutingInfo& routing_info);
 
 std::string ModelSafeRoutingInfoToString(
     const ModelSafeRoutingInfo& routing_info);
 
 ModelTypeSet GetRoutingInfoTypes(const ModelSafeRoutingInfo& routing_info);
 
 ModelSafeGroup GetGroupForModelType(const ModelType type,
                                     const ModelSafeRoutingInfo& routes);
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_ENGINE_MODEL_SAFE_WORKER_H_