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Support stop or keep of child actors when parent is restarted, #25556

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* stash messages and signals while waiting for children to be stopped
* handle watch of other actors
* exception from unstash
* exception from first setup
* merge RestartSupervisor and BackoffSupervisor
* API change: restartWithLimit => restart.withLimit
* remove unused PreStart
* docs
* move BubblingSample to separate class
* fix: fail after more than limit in restart.withLimit when deferred factory throws
* match case RestartOrBackoff instead
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Patrik Nordwall 2019-01-17 16:48:22 +01:00 • committed by GitHub
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40
akka-docs/src/main/paradox/typed/fault-tolerance.md
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@ -1,7 +1,16 @@
# Fault Tolerance
When an actor throws an unexpected exception, a failure, while processing a message or during initialization, the actor
will by default be stopped. Note that there is an important distinction between failures and validation errors:
will by default be stopped.
@@@ note
An important difference between Typed and Untyped actors is that Typed actors are by default stopped if
an exception is thrown and no supervision strategy is defined while in Untyped they are restarted.
@@@
Note that there is an important distinction between failures and validation errors:
A validation error means that the data of a command sent to an actor is not valid, this should rather be modelled as a
part of the actor protocol than make the actor throw exceptions.
@ -74,6 +83,33 @@ Java
Each returned behavior will be re-wrapped automatically with the supervisor.
## Child actors are stopped when parent is restarting
Child actors are often started in a `setup` block that is run again when the parent actor is restarted.
The child actors are stopped to avoid resource leaks of creating new child actors each time the parent is restarted.
Scala
: @@snip [SupervisionCompileOnly.scala](/akka-actor-typed-tests/src/test/scala/docs/akka/typed/supervision/SupervisionCompileOnly.scala) { #restart-stop-children }
Java
: @@snip [SupervisionCompileOnlyTest.java](/akka-actor-typed-tests/src/test/java/jdocs/akka/typed/supervision/SupervisionCompileOnlyTest.java) { #restart-stop-children }
It is possible to override this so that child actors are not influenced when the parent actor is restarted.
The restarted parent instance will then have the same children as before the failure.
If child actors are created from `setup` like in the previous example and they should remain intact (not stopped)
when parent is restarted the `supervise` should be placed inside the `setup` and using
@scala[`SupervisorStrategy.restart.withStopChildren(false)`]@java[`SupervisorStrategy.restart().withStopChildren(false)`]
like this:
Scala
: @@snip [SupervisionCompileOnly.scala](/akka-actor-typed-tests/src/test/scala/docs/akka/typed/supervision/SupervisionCompileOnly.scala) { #restart-keep-children }
Java
: @@snip [SupervisionCompileOnlyTest.java](/akka-actor-typed-tests/src/test/java/jdocs/akka/typed/supervision/SupervisionCompileOnlyTest.java) { #restart-keep-children }
That means that the `setup` block will only be run when the parent actor is first started, and not when it is
restarted.
## Bubble failures up through the hierarchy
@ -98,4 +134,4 @@ Scala
: @@snip [FaultToleranceDocSpec.scala](/akka-actor-typed-tests/src/test/scala/docs/akka/typed/FaultToleranceDocSpec.scala) { #bubbling-example }
Java
: @@snip [SupervisionCompileOnlyTest.java](/akka-actor-typed-tests/src/test/java/jdocs/akka/typed/FaultToleranceDocTest.java) { #bubbling-example }
: @@snip [SupervisionCompileOnlyTest.java](/akka-actor-typed-tests/src/test/java/jdocs/akka/typed/BubblingSample.java) { #bubbling-example }