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Merge pull request #780 from akka/wip-2513-pattern-schedule-tick-to-self-ban

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Document how to schedule periodic messages from an actor to itself. #2513
This commit is contained in:
Björn Antonsson 2012-10-15 06:37:22 -07:00
commit 4a4465e439
4 changed files with 352 additions and 2 deletions
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191
akka-docs/rst/java/code/docs/pattern/SchedulerPatternTest.java Normal file
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@ -0,0 +1,191 @@
/**
* Copyright (C) 2009-2012 Typesafe Inc. <http://www.typesafe.com>
*/
package docs.pattern;
import akka.actor.*;
import akka.testkit.*;
import akka.testkit.TestEvent.Mute;
import akka.testkit.TestEvent.UnMute;
import org.junit.*;
import scala.concurrent.util.Duration;
import scala.concurrent.util.FiniteDuration;
import java.util.Arrays;
import java.util.concurrent.TimeUnit;
public class SchedulerPatternTest {
static ActorSystem system;
@BeforeClass
public static void setUp() {
system = ActorSystem.create("SchedulerPatternTest", AkkaSpec.testConf());
}
@AfterClass
public static void tearDown() {
system.shutdown();
}
static
//#schedule-constructor
public class ScheduleInConstructor extends UntypedActor {
private final Cancellable tick = getContext().system().scheduler().schedule(
Duration.create(500, TimeUnit.MILLISECONDS),
Duration.create(1000, TimeUnit.MILLISECONDS),
getSelf(), "tick", getContext().dispatcher());
//#schedule-constructor
// this variable and constructor is declared here to not show up in the docs
final ActorRef target;
public ScheduleInConstructor(ActorRef target) {
this.target = target;
}
//#schedule-constructor
@Override
public void postStop() {
tick.cancel();
}
@Override
public void onReceive(Object message) throws Exception {
if (message.equals("tick")) {
// do something useful here
//#schedule-constructor
target.tell(message, getSelf());
//#schedule-constructor
}
//#schedule-constructor
else if (message.equals("restart")) {
throw new ArithmeticException();
}
//#schedule-constructor
else {
unhandled(message);
}
}
}
//#schedule-constructor
static
//#schedule-receive
public class ScheduleInReceive extends UntypedActor {
//#schedule-receive
// this variable and constructor is declared here to not show up in the docs
final ActorRef target;
public ScheduleInReceive(ActorRef target) {
this.target = target;
}
//#schedule-receive
@Override
public void preStart() {
getContext().system().scheduler().scheduleOnce(
Duration.create(500, TimeUnit.MILLISECONDS),
getSelf(), "tick", getContext().dispatcher());
}
// override postRestart so we don't call preStart and schedule a new message
@Override
public void postRestart(Throwable reason) {
}
@Override
public void onReceive(Object message) throws Exception {
if (message.equals("tick")) {
// send another periodic tick after the specified delay
getContext().system().scheduler().scheduleOnce(
Duration.create(1000, TimeUnit.MILLISECONDS),
getSelf(), "tick", getContext().dispatcher());
// do something useful here
//#schedule-receive
target.tell(message, getSelf());
//#schedule-receive
}
//#schedule-receive
else if (message.equals("restart")) {
throw new ArithmeticException();
}
//#schedule-receive
else {
unhandled(message);
}
}
}
//#schedule-receive
@Test
@Ignore // no way to tag this as timing sensitive
public void scheduleInConstructor() {
new TestSchedule(system) {{
final JavaTestKit probe = new JavaTestKit(system);
final Props props = new Props(new UntypedActorFactory() {
public UntypedActor create() {
return new ScheduleInConstructor(probe.getRef());
}
});
testSchedule(probe, props, duration("3000 millis"), duration("2000 millis"));
}};
}
@Test
@Ignore // no way to tag this as timing sensitive
public void scheduleInReceive() {
new TestSchedule(system) {{
final JavaTestKit probe = new JavaTestKit(system);
final Props props = new Props(new UntypedActorFactory() {
public UntypedActor create() {
return new ScheduleInReceive(probe.getRef());
}
});
testSchedule(probe, props, duration("3000 millis"), duration("2500 millis"));
}};
}
public static class TestSchedule extends JavaTestKit {
private ActorSystem system;
public TestSchedule(ActorSystem system) {
super(system);
this.system = system;
}
public void testSchedule(final JavaTestKit probe, Props props,
FiniteDuration startDuration,
FiniteDuration afterRestartDuration) {
Iterable<akka.testkit.EventFilter> filter =
Arrays.asList(new akka.testkit.EventFilter[]{
(akka.testkit.EventFilter) new ErrorFilter(ArithmeticException.class)});
try {
system.eventStream().publish(new Mute(filter));
final ActorRef actor = system.actorOf(props);
new Within(startDuration) {
protected void run() {
probe.expectMsgEquals("tick");
probe.expectMsgEquals("tick");
probe.expectMsgEquals("tick");
}
};
actor.tell("restart", getRef());
new Within(afterRestartDuration) {
protected void run() {
probe.expectMsgEquals("tick");
probe.expectMsgEquals("tick");
}
};
system.stop(actor);
}
finally {
system.eventStream().publish(new UnMute(filter));
}
}
}
}

32
akka-docs/rst/java/howto.rst
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@ -17,6 +17,37 @@ sense to add to the ``akka.pattern`` package for creating an `OTP-like library
You might find some of the patterns described in the Scala chapter of You might find some of the patterns described in the Scala chapter of
:ref:`howto-scala` useful even though the example code is written in Scala. :ref:`howto-scala` useful even though the example code is written in Scala.
Scheduling Periodic Messages
============================
This pattern describes how to schedule periodic messages to yourself in two different
ways.
The first way is to set up periodic message scheduling in the constructor of the actor,
and cancel that scheduled sending in ``postStop`` or else we might have multiple registered
message sends to the same actor.
.. note::
With this approach the scheduled periodic message send will be restarted with the actor on restarts.
This also means that the time period that elapses between two tick messages during a restart may drift
off based on when you restart the scheduled message sends relative to the time that the last message was
sent, and how long the initial delay is. Worst case scenario is ``interval`` plus ``initialDelay``.
.. includecode:: code/docs/pattern/SchedulerPatternTest.java#schedule-constructor
The second variant sets up an initial one shot message send in the ``preStart`` method
of the actor, and the then the actor when it receives this message sets up a new one shot
message send. You also have to override ``postRestart`` so we don't call ``preStart``
and schedule the initial message send again.
.. note::
With this approach we won't fill up the mailbox with tick messages if the actor is
under pressure, but only schedule a new tick message when we have seen the previous one.
.. includecode:: code/docs/pattern/SchedulerPatternTest.java#schedule-receive
Template Pattern Template Pattern
================ ================
@ -33,4 +64,3 @@ This is an especially nice pattern, since it does even come with some empty exam
Spread the word: this is the easiest way to get famous! Spread the word: this is the easiest way to get famous!
Please keep this pattern at the end of this file. Please keep this pattern at the end of this file.

99
akka-docs/rst/scala/code/docs/pattern/SchedulerPatternSpec.scala Normal file
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@ -0,0 +1,99 @@
/**
* Copyright (C) 2009-2012 Typesafe Inc. <http://www.typesafe.com>
*/
package docs.pattern
import language.postfixOps
import akka.actor.{ Props, ActorRef, Actor }
import scala.concurrent.util.duration._
import scala.concurrent.util.{ FiniteDuration, Duration }
import akka.testkit.{ TimingTest, AkkaSpec, filterException }
import docs.pattern.SchedulerPatternSpec.ScheduleInConstructor
object SchedulerPatternSpec {
//#schedule-constructor
class ScheduleInConstructor extends Actor {
val tick =
context.system.scheduler.schedule(500 millis, 1000 millis, self, "tick")
//#schedule-constructor
// this var and constructor is declared here to not show up in the docs
var target: ActorRef = null
def this(target: ActorRef) = { this(); this.target = target }
//#schedule-constructor
override def postStop() = tick.cancel()
def receive = {
case "tick" ⇒
// do something useful here
//#schedule-constructor
target ! "tick"
case "restart" ⇒
throw new ArithmeticException
//#schedule-constructor
}
}
//#schedule-constructor
//#schedule-receive
class ScheduleInReceive extends Actor {
import context._
//#schedule-receive
// this var and constructor is declared here to not show up in the docs
var target: ActorRef = null
def this(target: ActorRef) = { this(); this.target = target }
//#schedule-receive
override def preStart() =
system.scheduler.scheduleOnce(500 millis, self, "tick")
// override postRestart so we don't call preStart and schedule a new message
override def postRestart(reason: Throwable) = {}
def receive = {
case "tick" ⇒
// send another periodic tick after the specified delay
system.scheduler.scheduleOnce(1000 millis, self, "tick")
// do something useful here
//#schedule-receive
target ! "tick"
case "restart" ⇒
throw new ArithmeticException
//#schedule-receive
}
}
//#schedule-receive
}
class SchedulerPatternSpec extends AkkaSpec {
def testSchedule(actor: ActorRef, startDuration: FiniteDuration,
afterRestartDuration: FiniteDuration) = {
filterException[ArithmeticException] {
within(startDuration) {
expectMsg("tick")
expectMsg("tick")
expectMsg("tick")
}
actor ! "restart"
within(afterRestartDuration) {
expectMsg("tick")
expectMsg("tick")
}
system.stop(actor)
}
}
"send periodic ticks from the constructor" taggedAs TimingTest in {
testSchedule(system.actorOf(Props(new ScheduleInConstructor(testActor))),
3000 millis, 2000 millis)
}
"send ticks from the preStart and receive" taggedAs TimingTest in {
testSchedule(system.actorOf(Props(new ScheduleInConstructor(testActor))),
3000 millis, 2500 millis)
}
}

32
akka-docs/rst/scala/howto.rst
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@ -111,6 +111,37 @@ This is where the Spider pattern comes in."
The pattern is described `Discovering Message Flows in Actor System with the Spider Pattern <http://letitcrash.com/post/30585282971/discovering-message-flows-in-actor-systems-with-the>`_. The pattern is described `Discovering Message Flows in Actor System with the Spider Pattern <http://letitcrash.com/post/30585282971/discovering-message-flows-in-actor-systems-with-the>`_.
Scheduling Periodic Messages
============================
This pattern describes how to schedule periodic messages to yourself in two different
ways.
The first way is to set up periodic message scheduling in the constructor of the actor,
and cancel that scheduled sending in ``postStop`` or else we might have multiple registered
message sends to the same actor.
.. note::
With this approach the scheduled periodic message send will be restarted with the actor on restarts.
This also means that the time period that elapses between two tick messages during a restart may drift
off based on when you restart the scheduled message sends relative to the time that the last message was
sent, and how long the initial delay is. Worst case scenario is ``interval`` plus ``initialDelay``.
.. includecode:: code/docs/pattern/SchedulerPatternSpec.scala#schedule-constructor
The second variant sets up an initial one shot message send in the ``preStart`` method
of the actor, and the then the actor when it receives this message sets up a new one shot
message send. You also have to override ``postRestart`` so we don't call ``preStart``
and schedule the initial message send again.
.. note::
With this approach we won't fill up the mailbox with tick messages if the actor is
under pressure, but only schedule a new tick message when we have seen the previous one.
.. includecode:: code/docs/pattern/SchedulerPatternSpec.scala#schedule-receive
Template Pattern Template Pattern
================ ================
@ -127,4 +158,3 @@ This is an especially nice pattern, since it does even come with some empty exam
Spread the word: this is the easiest way to get famous! Spread the word: this is the easiest way to get famous!
Please keep this pattern at the end of this file. Please keep this pattern at the end of this file.