base/message_loop/incoming_task_queue.h

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