调度器

注：本节未经校验，如有问题欢迎提issue

有时需要设定将来发生的事情，这时该怎么办? ActorSystem 就能搞定一切! 在那儿你能找到 scheduler 方法，它返回一个 akka.actor.Scheduler 实例, 这个实例在每个Actor系统里是唯一的，用来在内部指定一段时间后发生的行为。

请注意定时任务是使用 ActorSystem 的 MessageDispatcher 执行的.

你可以计划向actor发送消息或执行任务 (函数或Runnable). 你会得到一个 Cancellable 类型的返回值，你可以调用 cancel 来取消定时操作的执行。

警告

Akka中使用的Scheduler的默认实现是基于根据一个固定的时间表清空的工作桶。它不是在确切的时间执行任务，而是在每个时间刻度，它将运行 （结束） 到期的一切。可以通过akka.scheduler.tick-duration配置属性修改默认Scheduler的时间精度。

示例

1. import akka.actor.Actor
2. import akka.actor.Props
3. import scala.concurrent.duration._

5. //Use the system's dispatcher as ExecutionContext
6. import system.dispatcher

8. //Schedules to send the "foo"-message to the testActor after 50ms
9. system.scheduler.scheduleOnce(50 milliseconds, testActor, "foo")

1. //Schedules a function to be executed (send a message to the testActor) after 50ms
2. system.scheduler.scheduleOnce(50 milliseconds) {
3. testActor ! System.currentTimeMillis
4. }

1. val Tick = "tick"
2. class TickActor extends Actor {
3. def receive = {
4. case Tick => //Do something
5. }
6. }
7. val tickActor = system.actorOf(Props(classOf[TickActor], this))
8. //Use system's dispatcher as ExecutionContext
9. import system.dispatcher

11. //This will schedule to send the Tick-message
12. //to the tickActor after 0ms repeating every 50ms
13. val cancellable =
14. system.scheduler.schedule(0 milliseconds,
15. 50 milliseconds,
16. tickActor,
17. Tick)

19. //This cancels further Ticks to be sent
20. cancellable.cancel()

警告

如果你计划函数或Runnable实例时应该多加小心，不要关闭(闭合包含)不稳定的引用。在实践中这意味着在Actor实例中，不要在闭包中使用this，不直接访问 sender() 并且不要直接调用actor实例的方法。如果你需要安排一个调用，则安排一个发往self的消息 （包含必需的参数），然后在收到消息时再调用方法。

来自 akka.actor.ActorSystem

1. /**
2. * Light-weight scheduler for running asynchronous tasks after some deadline
3. * in the future. Not terribly precise but cheap.
4. */
5. def scheduler: Scheduler

Scheduler 接口

实际的调度程序实现是在 ActorSystem 启动时反射加载的，这意味着通过使用 akka.scheduler.implementation 配置属性它可能提供一个的不同实现。引用的类必须实现以下接口：

1. /**
2. * An Akka scheduler service. This one needs one special behavior: if
3. * Closeable, it MUST execute all outstanding tasks upon .close() in order
4. * to properly shutdown all dispatchers.
5. *
6. * Furthermore, this timer service MUST throw IllegalStateException if it
7. * cannot schedule a task. Once scheduled, the task MUST be executed. If
8. * executed upon close(), the task may execute before its timeout.
9. *
10. * Scheduler implementation are loaded reflectively at ActorSystem start-up
11. * with the following constructor arguments:
12. *  1) the system’s com.typesafe.config.Config (from system.settings.config)
13. *  2) a akka.event.LoggingAdapter
14. *  3) a java.util.concurrent.ThreadFactory
15. */
16. trait Scheduler {
17. /**
18. * Schedules a message to be sent repeatedly with an initial delay and
19. * frequency. E.g. if you would like a message to be sent immediately and
20. * thereafter every 500ms you would set delay=Duration.Zero and
21. * interval=Duration(500, TimeUnit.MILLISECONDS)
22. *
23. * Java & Scala API
24. */
25. final def schedule(
26. initialDelay: FiniteDuration,
27. interval: FiniteDuration,
28. receiver: ActorRef,
29. message: Any)(implicit executor: ExecutionContext,
30. sender: ActorRef = Actor.noSender): Cancellable =
31. schedule(initialDelay, interval, new Runnable {
32. def run = {
33. receiver ! message
34. if (receiver.isTerminated)
35. throw new SchedulerException("timer active for terminated actor")
36. }
37. })

39. /**
40. * Schedules a function to be run repeatedly with an initial delay and a
41. * frequency. E.g. if you would like the function to be run after 2 seconds
42. * and thereafter every 100ms you would set delay = Duration(2, TimeUnit.SECONDS)
43. * and interval = Duration(100, TimeUnit.MILLISECONDS)
44. *
45. * Scala API
46. */
47. final def schedule(
48. initialDelay: FiniteDuration,
49. interval: FiniteDuration)(f: ⇒ Unit)(
50. implicit executor: ExecutionContext): Cancellable =
51. schedule(initialDelay, interval, new Runnable { override def run = f })

53. /**
54. * Schedules a function to be run repeatedly with an initial delay and
55. * a frequency. E.g. if you would like the function to be run after 2
56. * seconds and thereafter every 100ms you would set delay = Duration(2,
57. * TimeUnit.SECONDS) and interval = Duration(100, TimeUnit.MILLISECONDS)
58. *
59. * Java API
60. */
61. def schedule(
62. initialDelay: FiniteDuration,
63. interval: FiniteDuration,
64. runnable: Runnable)(implicit executor: ExecutionContext): Cancellable

66. /**
67. * Schedules a message to be sent once with a delay, i.e. a time period that has
68. * to pass before the message is sent.
69. *
70. * Java & Scala API
71. */
72. final def scheduleOnce(
73. delay: FiniteDuration,
74. receiver: ActorRef,
75. message: Any)(implicit executor: ExecutionContext,
76. sender: ActorRef = Actor.noSender): Cancellable =
77. scheduleOnce(delay, new Runnable {
78. override def run = receiver ! message
79. })

81. /**
82. * Schedules a function to be run once with a delay, i.e. a time period that has
83. * to pass before the function is run.
84. *
85. * Scala API
86. */
87. final def scheduleOnce(delay: FiniteDuration)(f: ⇒ Unit)(
88. implicit executor: ExecutionContext): Cancellable =
89. scheduleOnce(delay, new Runnable { override def run = f })

91. /**
92. * Schedules a Runnable to be run once with a delay, i.e. a time period that
93. * has to pass before the runnable is executed.
94. *
95. * Java & Scala API
96. */
97. def scheduleOnce(
98. delay: FiniteDuration,
99. runnable: Runnable)(implicit executor: ExecutionContext): Cancellable

101. /**
102. * The maximum supported task frequency of this scheduler, i.e. the inverse
103. * of the minimum time interval between executions of a recurring task, in Hz.
104. */
105. def maxFrequency: Double

107. }

Cancellable 接口

它使你可以 取消 计划执行的任务。

警告 它不会中止已经启动的任务的执行。

调度的任务会返回一个 Cancellable （或抛出IllegalStateException时，如果在调度器关闭后尝试使用）。这允许你取消原定执行的东西。

警告

这不会中止已经开始执行的任务。检查cancel的返回值以检测已计划的任务是被取消，还是（最终）被运行。

1. /**
2. * Signifies something that can be cancelled
3. * There is no strict guarantee that the implementation is thread-safe,
4. * but it should be good practice to make it so.
5. */
6. trait Cancellable {
7. /**
8. * Cancels this Cancellable and returns true if that was successful.
9. * If this cancellable was (concurrently) cancelled already, then this method
10. * will return false although isCancelled will return true.
11. *
12. * Java & Scala API
13. */
14. def cancel(): Boolean

16. /**
17. * Returns true if and only if this Cancellable has been successfully cancelled
18. *
19. * Java & Scala API
20. */
21. def isCancelled: Boolean
22. }