1// Copyright (c) 2012 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_MAC_LIBDISPATCH_SEQUENCED_TASK_RUNNER_H_
6#define BASE_MAC_LIBDISPATCH_SEQUENCED_TASK_RUNNER_H_
7
8#include <dispatch/dispatch.h>
9
10#include "base/single_thread_task_runner.h"
11#include "base/synchronization/waitable_event.h"
12
13namespace base {
14namespace mac {
15
16// This is an implementation of the TaskRunner interface that runs closures on
17// a thread managed by Apple's libdispatch. This has the benefit of being able
18// to PostTask() and friends to a dispatch queue, while being reusable as a
19// dispatch_queue_t.
20//
21// One would use this class if an object lives exclusively on one thread but
22// needs a dispatch_queue_t for use in a system API. This ensures all dispatch
23// callbacks happen on the same thread as Closure tasks.
24//
25// A LibDispatchTaskRunner will continue to run until all references to the
26// underlying dispatch queue are released.
27//
28// Important Notes:
29//   - There is no MessageLoop running on this thread, and ::current() returns
30//     NULL.
31//   - No nested loops can be run, and all tasks are run non-nested.
32//   - Work scheduled via libdispatch runs at the same priority as and is
33//     interleaved with posted tasks, though FIFO order is guaranteed.
34//
35class BASE_EXPORT LibDispatchTaskRunner : public base::SingleThreadTaskRunner {
36 public:
37  // Starts a new serial dispatch queue with a given name.
38  explicit LibDispatchTaskRunner(const char* name);
39
40  // base::TaskRunner:
41  virtual bool PostDelayedTask(const tracked_objects::Location& from_here,
42                               const Closure& task,
43                               base::TimeDelta delay) OVERRIDE;
44  virtual bool RunsTasksOnCurrentThread() const OVERRIDE;
45
46  // base::SequencedTaskRunner:
47  virtual bool PostNonNestableDelayedTask(
48      const tracked_objects::Location& from_here,
49      const Closure& task,
50      base::TimeDelta delay) OVERRIDE;
51
52  // This blocks the calling thread until all work on the dispatch queue has
53  // been run and the queue has been destroyed. Destroying a queue requires
54  // ALL retained references to it to be released. Any new tasks posted to
55  // this thread after shutdown are dropped.
56  void Shutdown();
57
58  // Returns the dispatch queue associated with this task runner, for use with
59  // system APIs that take dispatch queues. The caller is responsible for
60  // retaining the result.
61  //
62  // All properties (context, finalizer, etc.) are managed by this class, and
63  // clients should only use the result of this for dispatch_async().
64  dispatch_queue_t GetDispatchQueue() const;
65
66 protected:
67  virtual ~LibDispatchTaskRunner();
68
69 private:
70  static void Finalizer(void* context);
71
72  dispatch_queue_t queue_;
73
74  // The event on which Shutdown waits until Finalizer runs.
75  base::WaitableEvent queue_finalized_;
76};
77
78}  // namespace mac
79}  // namespace base
80
81#endif  // BASE_MAC_LIBDISPATCH_SEQUENCED_TASK_RUNNER_H_
82