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      1 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #ifndef BASE_DEFERRED_SEQUENCED_TASKRUNNER_H_
      6 #define BASE_DEFERRED_SEQUENCED_TASKRUNNER_H_
      7 
      8 #include <vector>
      9 
     10 #include "base/base_export.h"
     11 #include "base/basictypes.h"
     12 #include "base/callback.h"
     13 #include "base/compiler_specific.h"
     14 #include "base/memory/ref_counted.h"
     15 #include "base/sequenced_task_runner.h"
     16 #include "base/synchronization/lock.h"
     17 #include "base/time/time.h"
     18 #include "base/tracked_objects.h"
     19 
     20 namespace base {
     21 
     22 // A DeferredSequencedTaskRunner is a subclass of SequencedTaskRunner that
     23 // queues up all requests until the first call to Start() is issued.
     24 class BASE_EXPORT DeferredSequencedTaskRunner : public SequencedTaskRunner {
     25  public:
     26   explicit DeferredSequencedTaskRunner(
     27       const scoped_refptr<SequencedTaskRunner>& target_runner);
     28 
     29   // TaskRunner implementation
     30   virtual bool PostDelayedTask(const tracked_objects::Location& from_here,
     31                                const Closure& task,
     32                                TimeDelta delay) OVERRIDE;
     33   virtual bool RunsTasksOnCurrentThread() const OVERRIDE;
     34 
     35   // SequencedTaskRunner implementation
     36   virtual bool PostNonNestableDelayedTask(
     37       const tracked_objects::Location& from_here,
     38       const Closure& task,
     39       TimeDelta delay) OVERRIDE;
     40 
     41   // Start the execution - posts all queued tasks to the target executor. The
     42   // deferred tasks are posted with their initial delay, meaning that the task
     43   // execution delay is actually measured from Start.
     44   // Fails when called a second time.
     45   void Start();
     46 
     47  private:
     48   struct DeferredTask  {
     49     DeferredTask();
     50     ~DeferredTask();
     51 
     52     tracked_objects::Location posted_from;
     53     Closure task;
     54     // The delay this task was initially posted with.
     55     TimeDelta delay;
     56     bool is_non_nestable;
     57   };
     58 
     59   virtual ~DeferredSequencedTaskRunner();
     60 
     61   // Creates a |Task| object and adds it to |deferred_tasks_queue_|.
     62   void QueueDeferredTask(const tracked_objects::Location& from_here,
     63                          const Closure& task,
     64                          TimeDelta delay,
     65                          bool is_non_nestable);
     66 
     67   // // Protects |started_| and |deferred_tasks_queue_|.
     68   mutable Lock lock_;
     69 
     70   bool started_;
     71   const scoped_refptr<SequencedTaskRunner> target_task_runner_;
     72   std::vector<DeferredTask> deferred_tasks_queue_;
     73 
     74   DISALLOW_COPY_AND_ASSIGN(DeferredSequencedTaskRunner);
     75 };
     76 
     77 }  // namespace base
     78 
     79 #endif  // BASE_DEFERRED_SEQUENCED_TASKRUNNER_H_
     80