[SyncFS] Make task invocation in SyncTaskRunner async

chrome/browser/sync_file_system/drive_backend/sync_task_manager.h

 // Copyright 2014 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 CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_SYNC_TASK_MANAGER_H_
 #define CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_SYNC_TASK_MANAGER_H_
 
 #include <queue>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/containers/scoped_ptr_hash_map.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/sequence_checker.h"
 #include "base/threading/non_thread_safe.h"
 #include "chrome/browser/sync_file_system/drive_backend/task_dependency_manager.h"
 #include "chrome/browser/sync_file_system/sync_callbacks.h"
 #include "chrome/browser/sync_file_system/sync_status_code.h"
 #include "chrome/browser/sync_file_system/task_logger.h"
 
+namespace base {
+class SequencedTaskRunner;
+}
+
 namespace tracked_objects {
 class Location;
 }
 
 namespace sync_file_system {
 namespace drive_backend {
 
 class SyncTask;
 class SyncTaskToken;
 struct BlockingFactor;
@@ skipping 29 matching lines @@
     virtual void NotifyLastOperationStatus(
         SyncStatusCode last_operation_status,
         bool last_operation_used_network) = 0;
 
     virtual void RecordTaskLog(scoped_ptr<TaskLogger::TaskLog> task_log) = 0;
   };
 
   // Runs at most |maximum_background_tasks| parallel as background tasks.
   // If |maximum_background_tasks| is zero, all task runs as foreground task.
   SyncTaskManager(base::WeakPtr<Client> client,
-                  size_t maximum_background_task);
+                  size_t maximum_background_task,
+                  base::SequencedTaskRunner* task_runner);
   virtual ~SyncTaskManager();
 
   // This needs to be called to start task scheduling.
   // If |status| is not SYNC_STATUS_OK calling this may change the
   // service status. This should not be called more than once.
   void Initialize(SyncStatusCode status);
 
   // Schedules a task at the given priority.
   void ScheduleTask(const tracked_objects::Location& from_here,
                     const Task& task,
@@ skipping 71 matching lines @@
   scoped_ptr<SyncTaskToken> GetTokenForBackgroundTask(
       const tracked_objects::Location& from_here,
       const SyncStatusCallback& callback,
       scoped_ptr<BlockingFactor> blocking_factor);
 
   void PushPendingTask(const base::Closure& closure, Priority priority);
 
   void RunTask(scoped_ptr<SyncTaskToken> token,
                scoped_ptr<SyncTask> task);
 
-  void StartNextTask();
+  // Runs a pending task as a foreground task if possible.
+  // If |token| is non-NULL, put |token| back to |token_| beforehand.
+  void MaybeStartNextForegroundTask(scoped_ptr<SyncTaskToken> token);
 
   base::WeakPtr<Client> client_;
 
   // Owns running SyncTask to cancel the task on SyncTaskManager deletion.
   scoped_ptr<SyncTask> running_foreground_task_;
 
   // Owns running backgrounded SyncTask to cancel the task on SyncTaskManager
   // deletion.
   base::ScopedPtrHashMap<int64, SyncTask> running_background_tasks_;
 
   size_t maximum_background_task_;
 
   // Holds pending continuation to move task to background.
   base::Closure pending_backgrounding_task_;
 
   std::priority_queue<PendingTask, std::vector<PendingTask>,
                       PendingTaskComparator> pending_tasks_;
   int64 pending_task_seq_;
   int64 task_token_seq_;
 
   // Absence of |token_| implies a task is running. Incoming tasks should
   // wait for the task to finish in |pending_tasks_| if |token_| is null.
   // Each task must take TaskToken instance from |token_| and must hold it
   // until it finished. And the task must return the instance through
   // NotifyTaskDone when the task finished.
   scoped_ptr<SyncTaskToken> token_;
 
   TaskDependencyManager dependency_manager_;
 
+  scoped_refptr<base::SequencedTaskRunner> task_runner_;
   base::SequenceChecker sequence_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncTaskManager);
 };
 
 }  // namespace drive_backend
 }  // namespace sync_file_system
 
 #endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_SYNC_TASK_MANAGER_H_