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Refactor example to make it easier to copy-paste #29578 (#29860)

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* Refactor example to make it clear #29578

Restructure example

* Fix formatting

* Right formatting to disable format checker
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Josep Prat 2020-12-07 09:47:18 +01:00 • committed by GitHub
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30
akka-docs/src/main/paradox/typed/routers.md
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@ -16,17 +16,17 @@ To use Akka Actor Typed, you must add the following dependency in your project:
## Introduction
In some cases it is useful to distribute messages of the same type over a set of actors, so that messages can be
processed in parallel - a single actor will only process one message at a time.
In some cases it is useful to distribute messages of the same type over a set of actors, so that messages can be
processed in parallel - a single actor will only process one message at a time.
The router itself is a behavior that is spawned into a running actor that will then forward any message sent to it
to one final recipient out of the set of routees.
There are two kinds of routers included in Akka Typed - the pool router and the group router.
There are two kinds of routers included in Akka Typed - the pool router and the group router.
## Pool Router
The pool router is created with a routee `Behavior` and spawns a number of children with that behavior which it will
The pool router is created with a routee `Behavior` and spawns a number of children with that behavior which it will
then forward messages to.
If a child is stopped the pool router removes it from its set of routees. When the last child stops the router itself stops.
@ -34,6 +34,16 @@ To make a resilient router that deals with failures the routee `Behavior` must b
As actor children are always local the routees are never spread across a cluster with a pool router.
Let's first introduce the routee:
Scala
: @@snip [RouterSpec.scala](/akka-actor-typed-tests/src/test/scala/docs/akka/typed/RouterSpec.scala) { #routee }
Java
: @@snip [RouterTest.java](/akka-actor-typed-tests/src/test/java/jdocs/akka/typed/RouterTest.java) { #routee }
After having defined the routee, we can now concentrate on configuring the router itself. Note again the the router is an Actor in itself:
Scala
: @@snip [RouterSpec.scala](/akka-actor-typed-tests/src/test/scala/docs/akka/typed/RouterSpec.scala) { #pool }
@ -61,7 +71,7 @@ Since the receptionist is used this means the group router is cluster-aware out
messages to registered actors on any node in the cluster that is reachable. If no reachable actor exists the router
will fallback and route messages to actors on nodes marked as unreachable.
That the receptionist is used also means that the set of routees is eventually consistent, and that immediately when
That the receptionist is used also means that the set of routees is eventually consistent, and that immediately when
the group router is started the set of routees it knows about is empty, until it has seen a listing from the receptionist
it stashes incoming messages and forwards them as soon as it gets a listing from the receptionist.
@ -74,7 +84,6 @@ Scala
Java
: @@snip [RouterTest.java](/akka-actor-typed-tests/src/test/java/jdocs/akka/typed/RouterTest.java) { #group }
## Routing strategies
There are three different strategies for selecting which routee a message is forwarded to that can be selected
@ -84,7 +93,7 @@ Scala
: @@snip [RouterSpec.scala](/akka-actor-typed-tests/src/test/scala/docs/akka/typed/RouterSpec.scala) { #strategy }
Java
: @@snip [RouterTest.java](/akka-actor-typed-tests/src/test/java/jdocs/akka/typed/RouterTest.java) { #strategy }
: @@snip [RouterTest.java](/akka-actor-typed-tests/src/test/java/jdocs/akka/typed/RouterTest.java) { #strategy }
### Round Robin
@ -98,7 +107,6 @@ This is the default for pool routers as the pool of routees is expected to remai
An optional parameter `preferLocalRoutees` can be used for this strategy. Routers will only use routees located in local actor system if `preferLocalRoutees` is true and local routees do exist. The default value for this parameter is false.
### Random
Randomly selects a routee when a message is sent through the router.
@ -108,9 +116,9 @@ This is the default for group routers as the group of routees is expected to cha
An optional parameter `preferLocalRoutees` can be used for this strategy. Routers will only use routees located in local actor system if `preferLocalRoutees` is true and local routees do exist. The default value for this parameter is false.
### Consistent Hashing
Uses [consistent hashing](https://en.wikipedia.org/wiki/Consistent_hashing) to select a routee based
on the sent message. This [article](http://www.tom-e-white.com/2007/11/consistent-hashing.html)
on the sent message. This [article](http://www.tom-e-white.com/2007/11/consistent-hashing.html)
gives good insight into how consistent hashing is implemented.
Currently you have to define hashMapping of the router to map incoming messages to their consistent
@ -125,7 +133,7 @@ See also @ref[Akka Cluster Sharding](cluster-sharding.md) which provides stable
Note that if the routees are sharing a resource, the resource will determine if increasing the number of
actors will actually give higher throughput or faster answers. For example if the routees are CPU bound actors
it will not give better performance to create more routees than there are threads to execute the actors.
it will not give better performance to create more routees than there are threads to execute the actors.
Since the router itself is an actor and has a mailbox this means that messages are routed sequentially to the routees
where it can be processed in parallel (depending on the available threads in the dispatcher).