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
15namespace base {
16
17class MessageLoop;
18class WaitableEvent;
19
20namespace 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.
25class 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