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      1 // Copyright 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_MESSAGE_LOOP_INCOMING_TASK_QUEUE_H_
      6 #define BASE_MESSAGE_LOOP_INCOMING_TASK_QUEUE_H_
      7 
      8 #include "base/base_export.h"
      9 #include "base/macros.h"
     10 #include "base/memory/ref_counted.h"
     11 #include "base/pending_task.h"
     12 #include "base/synchronization/lock.h"
     13 #include "base/time/time.h"
     14 
     15 namespace base {
     16 
     17 class MessageLoop;
     18 class WaitableEvent;
     19 
     20 namespace internal {
     21 
     22 // Implements a queue of tasks posted to the message loop running on the current
     23 // thread. This class takes care of synchronizing posting tasks from different
     24 // threads and together with MessageLoop ensures clean shutdown.
     25 class BASE_EXPORT IncomingTaskQueue
     26     : public RefCountedThreadSafe<IncomingTaskQueue> {
     27  public:
     28   explicit IncomingTaskQueue(MessageLoop* message_loop);
     29 
     30   // Appends a task to the incoming queue. Posting of all tasks is routed though
     31   // AddToIncomingQueue() or TryAddToIncomingQueue() to make sure that posting
     32   // task is properly synchronized between different threads.
     33   //
     34   // Returns true if the task was successfully added to the queue, otherwise
     35   // returns false. In all cases, the ownership of |task| is transferred to the
     36   // called method.
     37   bool AddToIncomingQueue(const tracked_objects::Location& from_here,
     38                           const Closure& task,
     39                           TimeDelta delay,
     40                           bool nestable);
     41 
     42   // Returns true if the queue contains tasks that require higher than default
     43   // timer resolution. Currently only needed for Windows.
     44   bool HasHighResolutionTasks();
     45 
     46   // Returns true if the message loop is "idle". Provided for testing.
     47   bool IsIdleForTesting();
     48 
     49   // Loads tasks from the |incoming_queue_| into |*work_queue|. Must be called
     50   // from the thread that is running the loop. Returns the number of tasks that
     51   // require high resolution timers.
     52   int ReloadWorkQueue(TaskQueue* work_queue);
     53 
     54   // Disconnects |this| from the parent message loop.
     55   void WillDestroyCurrentMessageLoop();
     56 
     57   // This should be called when the message loop becomes ready for
     58   // scheduling work.
     59   void StartScheduling();
     60 
     61  private:
     62   friend class RefCountedThreadSafe<IncomingTaskQueue>;
     63   virtual ~IncomingTaskQueue();
     64 
     65   // Calculates the time at which a PendingTask should run.
     66   TimeTicks CalculateDelayedRuntime(TimeDelta delay);
     67 
     68   // Adds a task to |incoming_queue_|. The caller retains ownership of
     69   // |pending_task|, but this function will reset the value of
     70   // |pending_task->task|. This is needed to ensure that the posting call stack
     71   // does not retain |pending_task->task| beyond this function call.
     72   bool PostPendingTask(PendingTask* pending_task);
     73 
     74   // Wakes up the message loop and schedules work.
     75   void ScheduleWork();
     76 
     77   // Number of tasks that require high resolution timing. This value is kept
     78   // so that ReloadWorkQueue() completes in constant time.
     79   int high_res_task_count_;
     80 
     81   // The lock that protects access to the members of this class.
     82   base::Lock incoming_queue_lock_;
     83 
     84   // An incoming queue of tasks that are acquired under a mutex for processing
     85   // on this instance's thread. These tasks have not yet been been pushed to
     86   // |message_loop_|.
     87   TaskQueue incoming_queue_;
     88 
     89   // Points to the message loop that owns |this|.
     90   MessageLoop* message_loop_;
     91 
     92   // The next sequence number to use for delayed tasks.
     93   int next_sequence_num_;
     94 
     95   // True if our message loop has already been scheduled and does not need to be
     96   // scheduled again until an empty reload occurs.
     97   bool message_loop_scheduled_;
     98 
     99   // True if we always need to call ScheduleWork when receiving a new task, even
    100   // if the incoming queue was not empty.
    101   const bool always_schedule_work_;
    102 
    103   // False until StartScheduling() is called.
    104   bool is_ready_for_scheduling_;
    105 
    106   DISALLOW_COPY_AND_ASSIGN(IncomingTaskQueue);
    107 };
    108 
    109 }  // namespace internal
    110 }  // namespace base
    111 
    112 #endif  // BASE_MESSAGE_LOOP_INCOMING_TASK_QUEUE_H_
    113