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Docs: revise Coordinated Shutdown with new actors APIs (#29057)

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64
akka-docs/src/main/paradox/coordinated-shutdown.md
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@ -1,37 +1,39 @@
# Coordinated Shutdown
Under normal conditions when `ActorSystem` is terminated or the JVM process is shut down certain
Under normal conditions, when an `ActorSystem` is terminated or the JVM process is shut down, certain
actors and services will be stopped in a specific order.
This is handled by an extension named `CoordinatedShutdown`. It will run the registered tasks
during the shutdown process. The order of the shutdown phases is defined in configuration `akka.coordinated-shutdown.phases`.
The default phases are defined as:
The @apidoc[CoordinatedShutdown$] extension registers internal and user-defined tasks to be executed during the shutdown process. The tasks are grouped in configuration-defined "phases" which define the shutdown order.
@@snip [reference.conf](/akka-actor/src/main/resources/reference.conf) { #coordinated-shutdown-phases }
More phases can be added in the application's configuration if needed by overriding a phase with an
additional `depends-on`. Especially the phases `before-service-unbind`, `before-cluster-shutdown` and
Especially the phases `before-service-unbind`, `before-cluster-shutdown` and
`before-actor-system-terminate` are intended for application specific phases or tasks.
The order of the shutdown phases is defined in configuration `akka.coordinated-shutdown.phases`. See the default phases in the `reference.conf` tab:
Most relevant default phases
: | Phase | Description |
|-------------|----------------------------------------------|
| before-service-unbind | The first pre-defined phase during shutdown. |
| before-cluster-shutdown | Phase for custom application tasks that are to be run after service shutdown and before cluster shutdown. |
| before-actor-system-terminate | Phase for custom application tasks that are to be run after cluster shutdown and before `ActorSystem` termination. |
reference.conf (HOCON)
: @@snip [reference.conf](/akka-actor/src/main/resources/reference.conf) { #coordinated-shutdown-phases }
More phases can be added in the application's `application.conf` if needed by overriding a phase with an
additional `depends-on`.
The default phases are defined in a single linear order, but the phases can be ordered as a
directed acyclic graph (DAG) by defining the dependencies between the phases.
The phases are ordered with [topological](https://en.wikipedia.org/wiki/Topological_sorting) sort of the DAG.
Tasks can be added to a phase with:
Tasks can be added to a phase like in this example which allows a certain actor to react before termination starts:
Scala
: @@snip [ActorDocSpec.scala](/akka-docs/src/test/scala/docs/actor/ActorDocSpec.scala) { #coordinated-shutdown-addTask }
: @@snip [snip](/akka-docs/src/test/scala/docs/actor/typed/CoordinatedActorShutdownSpec.scala) { #coordinated-shutdown-addTask }
Java
: @@snip [ActorDocTest.java](/akka-docs/src/test/java/jdocs/actor/ActorDocTest.java) { #coordinated-shutdown-addTask }
If cancellation of previously added tasks is required:
Scala
: @@snip [ActorDocSpec.scala](/akka-docs/src/test/scala/docs/actor/ActorDocSpec.scala) { #coordinated-shutdown-cancellable }
Java
: @@snip [ActorDocTest.java](/akka-docs/src/test/java/jdocs/actor/ActorDocTest.java) { #coordinated-shutdown-cancellable }
: @@snip [snip](/akka-docs/src/test/java/jdocs/actor/typed/CoordinatedActorShutdownTest.java) { #coordinated-shutdown-addTask }
The returned @scala[`Future[Done]`] @java[`CompletionStage<Done>`] should be completed when the task is completed. The task name parameter
is only used for debugging/logging.
@ -43,9 +45,17 @@ If tasks are not completed within a configured timeout (see @ref:[reference.conf
the next phase will be started anyway. It is possible to configure `recover=off` for a phase
to abort the rest of the shutdown process if a task fails or is not completed within the timeout.
If cancellation of previously added tasks is required:
Scala
: @@snip [snip](/akka-docs/src/test/scala/docs/actor/typed/CoordinatedActorShutdownSpec.scala) { #coordinated-shutdown-cancellable }
Java
: @@snip [snip](/akka-docs/src/test/java/jdocs/actor/typed/CoordinatedActorShutdownTest.java) { #coordinated-shutdown-cancellable }
In the above example, it may be more convenient to simply stop the actor when it's done shutting down, rather than send back a done message,
and for the shutdown task to not complete until the actor is terminated. A convenience method is provided that adds a task that sends
a message to the actor and then watches its termination:
a message to the actor and then watches its termination (there is currently no corresponding functionality for the new actors API @github[see #29056](#29056)):
Scala
: @@snip [ActorDocSpec.scala](/akka-docs/src/test/scala/docs/actor/ActorDocSpec.scala) { #coordinated-shutdown-addActorTerminationTask }
@ -57,14 +67,14 @@ Tasks should typically be registered as early as possible after system startup.
the coordinated shutdown tasks that have been registered will be performed but tasks that are
added too late will not be run.
To start the coordinated shutdown process you can invoke @scala[`run`] @java[`runAll`] on the `CoordinatedShutdown`
extension:
To start the coordinated shutdown process you can either invoke `terminate()` on the `ActorSystem`, or @scala[`run`] @java[`runAll`] on the `CoordinatedShutdown`
extension and pass it a class implementing @apidoc[CoordinatedShutdown.Reason] for informational purposes:
Scala
: @@snip [ActorDocSpec.scala](/akka-docs/src/test/scala/docs/actor/ActorDocSpec.scala) { #coordinated-shutdown-run }
: @@snip [snip](/akka-docs/src/test/scala/docs/actor/typed/CoordinatedActorShutdownSpec.scala) { #coordinated-shutdown-run }
Java
: @@snip [ActorDocTest.java](/akka-docs/src/test/java/jdocs/actor/ActorDocTest.java) { #coordinated-shutdown-run }
: @@snip [snip](/akka-docs/src/test/java/jdocs/actor/typed/CoordinatedActorShutdownTest.java) { #coordinated-shutdown-run }
It's safe to call the @scala[`run`] @java[`runAll`] method multiple times. It will only run once.
@ -76,7 +86,7 @@ To enable a hard `System.exit` as a final action you can configure:
akka.coordinated-shutdown.exit-jvm = on
```
The coordinated shutdown process can also be started by calling `ActorSystem.terminate()`.
The coordinated shutdown process is also started once the actor system's root actor is stopped.
When using @ref:[Akka Cluster](cluster-usage.md) the `CoordinatedShutdown` will automatically run
when the cluster node sees itself as `Exiting`, i.e. leaving from another node will trigger
@ -96,10 +106,10 @@ If you have application specific JVM shutdown hooks it's recommended that you re
those shutting down Akka Remoting (Artery).
Scala
: @@snip [ActorDocSpec.scala](/akka-docs/src/test/scala/docs/actor/ActorDocSpec.scala) { #coordinated-shutdown-jvm-hook }
: @@snip [snip](/akka-docs/src/test/scala/docs/actor/typed/CoordinatedActorShutdownSpec.scala) { #coordinated-shutdown-jvm-hook }
Java
: @@snip [ActorDocTest.java](/akka-docs/src/test/java/jdocs/actor/ActorDocTest.java) { #coordinated-shutdown-jvm-hook }
: @@snip [snip](/akka-docs/src/test/java/jdocs/actor/typed/CoordinatedActorShutdownTest.java) { #coordinated-shutdown-jvm-hook }
For some tests it might be undesired to terminate the `ActorSystem` via `CoordinatedShutdown`.
You can disable that by adding the following to the configuration of the `ActorSystem` that is

42
akka-docs/src/test/java/jdocs/actor/ActorDocTest.java
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@ -847,51 +847,11 @@ public class ActorDocTest extends AbstractJavaTest {
};
}
private CompletionStage<Done> cleanup() {
return null;
}
@Test
public void coordinatedShutdown() {
final ActorRef someActor = system.actorOf(Props.create(FirstActor.class));
// #coordinated-shutdown-addTask
CoordinatedShutdown.get(system)
.addTask(
CoordinatedShutdown.PhaseBeforeServiceUnbind(),
"someTaskName",
() -> {
return akka.pattern.Patterns.ask(someActor, "stop", Duration.ofSeconds(5))
.thenApply(reply -> Done.getInstance());
});
// #coordinated-shutdown-addTask
// #coordinated-shutdown-cancellable
Cancellable cancellable =
CoordinatedShutdown.get(system)
.addCancellableTask(
CoordinatedShutdown.PhaseBeforeServiceUnbind(), "someTaskCleanup", () -> cleanup());
// much later...
cancellable.cancel();
// #coordinated-shutdown-cancellable
// #coordinated-shutdown-jvm-hook
CoordinatedShutdown.get(system)
.addJvmShutdownHook(() -> System.out.println("custom JVM shutdown hook..."));
// #coordinated-shutdown-jvm-hook
// don't run this
if (false) {
// #coordinated-shutdown-run
CompletionStage<Done> done =
CoordinatedShutdown.get(system).runAll(CoordinatedShutdown.unknownReason());
// #coordinated-shutdown-run
}
}
@Test
public void coordinatedShutdownActorTermination() {
ActorRef someActor = system.actorOf(Props.create(FirstActor.class));
someActor.tell(PoisonPill.getInstance(), ActorRef.noSender());
// https://github.com/akka/akka/issues/29056
// #coordinated-shutdown-addActorTerminationTask
CoordinatedShutdown.get(system)
.addActorTerminationTask(

133
akka-docs/src/test/java/jdocs/actor/typed/CoordinatedActorShutdownTest.java Normal file
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@ -0,0 +1,133 @@
/*
* Copyright (C) 2020 Lightbend Inc. <https://www.lightbend.com>
*/
package jdocs.actor.typed;
import akka.Done;
import akka.actor.Cancellable;
import akka.actor.CoordinatedShutdown;
import akka.actor.typed.ActorRef;
import akka.actor.typed.ActorSystem;
import akka.actor.typed.Behavior;
import akka.actor.typed.javadsl.*;
// #coordinated-shutdown-addTask
import static akka.actor.typed.javadsl.AskPattern.ask;
// #coordinated-shutdown-addTask
import java.time.Duration;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionStage;
public class CoordinatedActorShutdownTest {
// #coordinated-shutdown-addTask
public static class MyActor extends AbstractBehavior<MyActor.Messages> {
interface Messages {}
// ...
static final class Stop implements Messages {
final ActorRef<Done> replyTo;
Stop(ActorRef<Done> replyTo) {
this.replyTo = replyTo;
}
}
// #coordinated-shutdown-addTask
public static Behavior<Messages> create() {
return Behaviors.setup(MyActor::new);
}
private MyActor(ActorContext<Messages> context) {
super(context);
}
// #coordinated-shutdown-addTask
@Override
public Receive<Messages> createReceive() {
return newReceiveBuilder().onMessage(Stop.class, this::stop).build();
}
private Behavior<Messages> stop(Stop stop) {
// shut down the actor internal
// ...
stop.replyTo.tell(Done.done());
return Behaviors.stopped();
}
}
// #coordinated-shutdown-addTask
public static class Root extends AbstractBehavior<Void> {
public static Behavior<Void> create() {
return Behaviors.setup(
context -> {
ActorRef<MyActor.Messages> myActor = context.spawn(MyActor.create(), "my-actor");
ActorSystem<Void> system = context.getSystem();
// #coordinated-shutdown-addTask
CoordinatedShutdown.get(system)
.addTask(
CoordinatedShutdown.PhaseBeforeServiceUnbind(),
"someTaskName",
() ->
ask(myActor, MyActor.Stop::new, Duration.ofSeconds(5), system.scheduler()));
// #coordinated-shutdown-addTask
return Behaviors.empty();
});
}
private Root(ActorContext<Void> context) {
super(context);
}
@Override
public Receive<Void> createReceive() {
return newReceiveBuilder().build();
}
}
private CompletionStage<Done> cleanup() {
return CompletableFuture.completedFuture(Done.done());
}
public void mount() {
ActorSystem<Void> system = ActorSystem.create(Root.create(), "main");
// #coordinated-shutdown-cancellable
Cancellable cancellable =
CoordinatedShutdown.get(system)
.addCancellableTask(
CoordinatedShutdown.PhaseBeforeServiceUnbind(), "someTaskCleanup", () -> cleanup());
// much later...
cancellable.cancel();
// #coordinated-shutdown-cancellable
// #coordinated-shutdown-jvm-hook
CoordinatedShutdown.get(system)
.addJvmShutdownHook(() -> System.out.println("custom JVM shutdown hook..."));
// #coordinated-shutdown-jvm-hook
// don't run this
if (false) {
// #coordinated-shutdown-run
// shut down with `ActorSystemTerminateReason`
system.terminate();
// or define a specific reason
class UserInitiatedShutdown implements CoordinatedShutdown.Reason {
@Override
public String toString() {
return "UserInitiatedShutdown";
}
}
CompletionStage<Done> done =
CoordinatedShutdown.get(system).runAll(new UserInitiatedShutdown());
// #coordinated-shutdown-run
}
}
}

43
akka-docs/src/test/scala/docs/actor/ActorDocSpec.scala
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@ -724,34 +724,8 @@ class ActorDocSpec extends AkkaSpec("""
}
"using CoordinatedShutdown" in {
val someActor = system.actorOf(Props(classOf[Replier], this))
//#coordinated-shutdown-addTask
CoordinatedShutdown(system).addTask(CoordinatedShutdown.PhaseBeforeServiceUnbind, "someTaskName") { () =>
import akka.pattern.ask
import system.dispatcher
implicit val timeout = Timeout(5.seconds)
(someActor ? "stop").map(_ => Done)
}
//#coordinated-shutdown-addTask
{
def cleanup(): Unit = {}
import system.dispatcher
//#coordinated-shutdown-cancellable
val c = CoordinatedShutdown(system).addCancellableTask(CoordinatedShutdown.PhaseBeforeServiceUnbind, "cleanup") {
() =>
Future {
cleanup()
Done
}
}
// much later...
c.cancel()
//#coordinated-shutdown-cancellable
}
{
// other snippets moved to docs.actor.typed.CoordinatedActorShutdownSpec
{ // https://github.com/akka/akka/issues/29056
val someActor = system.actorOf(Props(classOf[Replier], this))
someActor ! PoisonPill
//#coordinated-shutdown-addActorTerminationTask
@ -762,19 +736,6 @@ class ActorDocSpec extends AkkaSpec("""
Some("stop"))
//#coordinated-shutdown-addActorTerminationTask
}
//#coordinated-shutdown-jvm-hook
CoordinatedShutdown(system).addJvmShutdownHook {
println("custom JVM shutdown hook...")
}
//#coordinated-shutdown-jvm-hook
// don't run this
def dummy(): Unit = {
//#coordinated-shutdown-run
val done: Future[Done] = CoordinatedShutdown(system).run(CoordinatedShutdown.UnknownReason)
//#coordinated-shutdown-run
}
}
}

91
akka-docs/src/test/scala/docs/actor/typed/CoordinatedActorShutdownSpec.scala Normal file
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@ -0,0 +1,91 @@
/*
* Copyright (C) 2020 Lightbend Inc. <https://www.lightbend.com>
*/
package docs.actor.typed
import akka.Done
import akka.actor.{ Cancellable, CoordinatedShutdown }
import akka.actor.typed.{ ActorRef, ActorSystem, Behavior }
import akka.actor.typed.scaladsl.Behaviors
import akka.actor.typed.scaladsl.AskPattern._
import akka.util.Timeout
import scala.concurrent.Future
import scala.concurrent.duration._
class CoordinatedActorShutdownSpec {
//#coordinated-shutdown-addTask
object MyActor {
trait Messages
case class Stop(replyTo: ActorRef[Done]) extends Messages
def behavior: Behavior[Messages] =
Behaviors.receiveMessage {
// ...
case Stop(replyTo) =>
// shut down the actor internals
// ..
replyTo.tell(Done)
Behaviors.stopped
}
}
//#coordinated-shutdown-addTask
trait Message
def root: Behavior[Message] = Behaviors.setup[Message] { context =>
implicit val system = context.system
val myActor = context.spawn(MyActor.behavior, "my-actor")
//#coordinated-shutdown-addTask
CoordinatedShutdown(context.system).addTask(CoordinatedShutdown.PhaseBeforeServiceUnbind, "someTaskName") { () =>
implicit val timeout = Timeout(5.seconds)
myActor.ask(MyActor.Stop)
}
//#coordinated-shutdown-addTask
Behaviors.empty
}
def showCancel: Unit = {
val system = ActorSystem(root, "main")
def cleanup(): Unit = {}
import system.executionContext
//#coordinated-shutdown-cancellable
val c: Cancellable =
CoordinatedShutdown(system).addCancellableTask(CoordinatedShutdown.PhaseBeforeServiceUnbind, "cleanup") { () =>
Future {
cleanup()
Done
}
}
// much later...
c.cancel()
//#coordinated-shutdown-cancellable
//#coordinated-shutdown-jvm-hook
CoordinatedShutdown(system).addJvmShutdownHook {
println("custom JVM shutdown hook...")
}
//#coordinated-shutdown-jvm-hook
// don't run this
def dummy(): Unit = {
//#coordinated-shutdown-run
// shut down with `ActorSystemTerminateReason`
system.terminate()
// or define a specific reason
case object UserInitiatedShutdown extends CoordinatedShutdown.Reason
val done: Future[Done] = CoordinatedShutdown(system).run(UserInitiatedShutdown)
//#coordinated-shutdown-run
}
}
}