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