Merge paradox/scala/mailboxes.md and java/mailboxes.md (#23191)
This commit is contained in:
Yu Nishiyama (a.k.a Richard)
Arnout Engelen
parent
2b2923f1b6
commit
71175eaf54
4 changed files with 87 additions and 297 deletions
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@ -1,273 +0,0 @@
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# Mailboxes
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An Akka `Mailbox` holds the messages that are destined for an `Actor`.
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Normally each `Actor` has its own mailbox, but with for example a `BalancingPool`
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all routees will share a single mailbox instance.
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## Mailbox Selection
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### Requiring a Message Queue Type for an Actor
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It is possible to require a certain type of message queue for a certain type of actor
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by having that actor implement the parameterized interface `RequiresMessageQueue`. Here is
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an example:
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@@snip [MyBoundedActor.java]($code$/java/jdocs/actor/MyBoundedActor.java) { #my-bounded-untyped-actor }
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The type parameter to the `RequiresMessageQueue` interface needs to be mapped to a mailbox in
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configuration like this:
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@@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #bounded-mailbox-config #required-mailbox-config }
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Now every time you create an actor of type `MyBoundedActor` it will try to get a bounded
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mailbox. If the actor has a different mailbox configured in deployment, either directly or via
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a dispatcher with a specified mailbox type, then that will override this mapping.
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@@@ note
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The type of the queue in the mailbox created for an actor will be checked against the required type in the
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interface and if the queue doesn't implement the required type then actor creation will fail.
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@@@
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### Requiring a Message Queue Type for a Dispatcher
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A dispatcher may also have a requirement for the mailbox type used by the
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actors running on it. An example is the BalancingDispatcher which requires a
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message queue that is thread-safe for multiple concurrent consumers. Such a
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requirement is formulated within the dispatcher configuration section like
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this:
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```
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my-dispatcher {
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mailbox-requirement = org.example.MyInterface
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}
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```
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The given requirement names a class or interface which will then be ensured to
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be a supertype of the message queue’s implementation. In case of a
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conflict—e.g. if the actor requires a mailbox type which does not satisfy this
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requirement—then actor creation will fail.
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### How the Mailbox Type is Selected
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When an actor is created, the `ActorRefProvider` first determines the
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dispatcher which will execute it. Then the mailbox is determined as follows:
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1. If the actor’s deployment configuration section contains a `mailbox` key
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then that names a configuration section describing the mailbox type to be
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used.
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2. If the actor’s `Props` contains a mailbox selection—i.e. `withMailbox`
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was called on it—then that names a configuration section describing the
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mailbox type to be used.
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3. If the dispatcher’s configuration section contains a `mailbox-type` key
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the same section will be used to configure the mailbox type.
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4. If the actor requires a mailbox type as described above then the mapping for
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that requirement will be used to determine the mailbox type to be used; if
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that fails then the dispatcher’s requirement—if any—will be tried instead.
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5. If the dispatcher requires a mailbox type as described above then the
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mapping for that requirement will be used to determine the mailbox type to
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be used.
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6. The default mailbox `akka.actor.default-mailbox` will be used.
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### Default Mailbox
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When the mailbox is not specified as described above the default mailbox
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is used. By default it is an unbounded mailbox, which is backed by a
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`java.util.concurrent.ConcurrentLinkedQueue`.
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`SingleConsumerOnlyUnboundedMailbox` is an even more efficient mailbox, and
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it can be used as the default mailbox, but it cannot be used with a BalancingDispatcher.
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Configuration of `SingleConsumerOnlyUnboundedMailbox` as default mailbox:
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```
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akka.actor.default-mailbox {
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mailbox-type = "akka.dispatch.SingleConsumerOnlyUnboundedMailbox"
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}
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```
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### Which Configuration is passed to the Mailbox Type
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Each mailbox type is implemented by a class which extends `MailboxType`
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and takes two constructor arguments: a `ActorSystem.Settings` object and
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a `Config` section. The latter is computed by obtaining the named
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configuration section from the actor system’s configuration, overriding its
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`id` key with the configuration path of the mailbox type and adding a
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fall-back to the default mailbox configuration section.
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## Builtin Mailbox Implementations
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Akka comes shipped with a number of mailbox implementations:
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*
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**UnboundedMailbox** (default)
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* The default mailbox
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* Backed by a `java.util.concurrent.ConcurrentLinkedQueue`
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* Blocking: No
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* Bounded: No
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* Configuration name: `"unbounded"` or `"akka.dispatch.UnboundedMailbox"`
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*
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**SingleConsumerOnlyUnboundedMailbox**
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This queue may or may not be faster than the default one depending on your use-case—be sure to benchmark properly!
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* Backed by a Multiple-Producer Single-Consumer queue, cannot be used with `BalancingDispatcher`
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* Blocking: No
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* Bounded: No
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* Configuration name: `"akka.dispatch.SingleConsumerOnlyUnboundedMailbox"`
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*
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**NonBlockingBoundedMailbox**
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* Backed by a very efficient Multiple-Producer Single-Consumer queue
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* Blocking: No (discards overflowing messages into deadLetters)
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* Bounded: Yes
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* Configuration name: `"akka.dispatch.NonBlockingBoundedMailbox"`
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*
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**UnboundedControlAwareMailbox**
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* Delivers messages that extend `akka.dispatch.ControlMessage` with higher priority
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* Backed by two `java.util.concurrent.ConcurrentLinkedQueue`
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* Blocking: No
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* Bounded: No
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* Configuration name: "akka.dispatch.UnboundedControlAwareMailbox"
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*
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**UnboundedPriorityMailbox**
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* Backed by a `java.util.concurrent.PriorityBlockingQueue`
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* Delivery order for messages of equal priority is undefined - contrast with the UnboundedStablePriorityMailbox
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* Blocking: No
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* Bounded: No
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* Configuration name: "akka.dispatch.UnboundedPriorityMailbox"
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*
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**UnboundedStablePriorityMailbox**
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* Backed by a `java.util.concurrent.PriorityBlockingQueue` wrapped in an `akka.util.PriorityQueueStabilizer`
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* FIFO order is preserved for messages of equal priority - contrast with the UnboundedPriorityMailbox
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* Blocking: No
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* Bounded: No
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* Configuration name: "akka.dispatch.UnboundedStablePriorityMailbox"
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Other bounded mailbox implementations which will block the sender if the capacity is reached and
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configured with non-zero `mailbox-push-timeout-time`.
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@@@ note
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The following mailboxes should only be used with zero `mailbox-push-timeout-time`.
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@@@
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* **BoundedMailbox**
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* Backed by a `java.util.concurrent.LinkedBlockingQueue`
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* Blocking: Yes if used with non-zero `mailbox-push-timeout-time`, otherwise No
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* Bounded: Yes
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* Configuration name: "bounded" or "akka.dispatch.BoundedMailbox"
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* **BoundedPriorityMailbox**
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* Backed by a `java.util.PriorityQueue` wrapped in an `akka.util.BoundedBlockingQueue`
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* Delivery order for messages of equal priority is undefined - contrast with the `BoundedStablePriorityMailbox`
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* Blocking: Yes if used with non-zero `mailbox-push-timeout-time`, otherwise No
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* Bounded: Yes
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* Configuration name: `"akka.dispatch.BoundedPriorityMailbox"`
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* **BoundedStablePriorityMailbox**
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* Backed by a `java.util.PriorityQueue` wrapped in an `akka.util.PriorityQueueStabilizer` and an `akka.util.BoundedBlockingQueue`
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* FIFO order is preserved for messages of equal priority - contrast with the BoundedPriorityMailbox
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* Blocking: Yes if used with non-zero `mailbox-push-timeout-time`, otherwise No
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* Bounded: Yes
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* Configuration name: "akka.dispatch.BoundedStablePriorityMailbox"
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* **BoundedControlAwareMailbox**
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* Delivers messages that extend `akka.dispatch.ControlMessage` with higher priority
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* Backed by two `java.util.concurrent.ConcurrentLinkedQueue` and blocking on enqueue if capacity has been reached
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* Blocking: Yes if used with non-zero `mailbox-push-timeout-time`, otherwise No
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* Bounded: Yes
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* Configuration name: "akka.dispatch.BoundedControlAwareMailbox"
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## Mailbox configuration examples
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### PriorityMailbox
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How to create a PriorityMailbox:
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@@snip [DispatcherDocTest.java]($code$/java/jdocs/dispatcher/DispatcherDocTest.java) { #prio-mailbox }
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And then add it to the configuration:
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@@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #prio-dispatcher-config }
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And then an example on how you would use it:
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@@snip [DispatcherDocTest.java]($code$/java/jdocs/dispatcher/DispatcherDocTest.java) { #prio-dispatcher }
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It is also possible to configure a mailbox type directly like this:
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@@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #prio-mailbox-config-java #mailbox-deployment-config }
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And then use it either from deployment like this:
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@@snip [DispatcherDocTest.java]($code$/java/jdocs/dispatcher/DispatcherDocTest.java) { #defining-mailbox-in-config }
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Or code like this:
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@@snip [DispatcherDocTest.java]($code$/java/jdocs/dispatcher/DispatcherDocTest.java) { #defining-mailbox-in-code }
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### ControlAwareMailbox
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A `ControlAwareMailbox` can be very useful if an actor needs to be able to receive control messages
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immediately no matter how many other messages are already in its mailbox.
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It can be configured like this:
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@@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #control-aware-mailbox-config }
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Control messages need to extend the `ControlMessage` trait:
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@@snip [DispatcherDocTest.java]($code$/java/jdocs/dispatcher/DispatcherDocTest.java) { #control-aware-mailbox-messages }
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And then an example on how you would use it:
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@@snip [DispatcherDocTest.java]($code$/java/jdocs/dispatcher/DispatcherDocTest.java) { #control-aware-dispatcher }
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## Creating your own Mailbox type
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An example is worth a thousand quacks:
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@@snip [MyUnboundedMailbox.java]($code$/java/jdocs/dispatcher/MyUnboundedMailbox.java) { #mailbox-implementation-example }
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@@snip [MyUnboundedMessageQueueSemantics.java]($code$/java/jdocs/dispatcher/MyUnboundedMessageQueueSemantics.java) { #mailbox-implementation-example }
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And then you just specify the FQCN of your MailboxType as the value of the "mailbox-type" in the dispatcher
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configuration, or the mailbox configuration.
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@@@ note
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Make sure to include a constructor which takes
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`akka.actor.ActorSystem.Settings` and `com.typesafe.config.Config`
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arguments, as this constructor is invoked reflectively to construct your
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mailbox type. The config passed in as second argument is that section from
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the configuration which describes the dispatcher or mailbox setting using
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this mailbox type; the mailbox type will be instantiated once for each
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dispatcher or mailbox setting using it.
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@@@
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You can also use the mailbox as a requirement on the dispatcher like this:
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@@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #custom-mailbox-config-java }
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Or by defining the requirement on your actor class like this:
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@@snip [DispatcherDocTest.java]($code$/java/jdocs/dispatcher/DispatcherDocTest.java) { #require-mailbox-on-actor }
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## Special Semantics of `system.actorOf`
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In order to make `system.actorOf` both synchronous and non-blocking while
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keeping the return type `ActorRef` (and the semantics that the returned
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ref is fully functional), special handling takes place for this case. Behind
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the scenes, a hollow kind of actor reference is constructed, which is sent to
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the system’s guardian actor who actually creates the actor and its context and
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puts those inside the reference. Until that has happened, messages sent to the
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`ActorRef` will be queued locally, and only upon swapping the real
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filling in will they be transferred into the real mailbox. Thus,
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```scala
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final Props props = ...
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// this actor uses MyCustomMailbox, which is assumed to be a singleton
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system.actorOf(props.withDispatcher("myCustomMailbox").tell("bang", sender);
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assert(MyCustomMailbox.getInstance().getLastEnqueued().equals("bang"));
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```
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will probably fail; you will have to allow for some time to pass and retry the
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check à la `TestKit.awaitCond`.
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1
akka-docs/src/main/paradox/java/mailboxes.md
Symbolic link
1
akka-docs/src/main/paradox/java/mailboxes.md
Symbolic link
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@ -0,0 +1 @@
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../scala/mailboxes.md
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@ -9,12 +9,16 @@ all routees will share a single mailbox instance.
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### Requiring a Message Queue Type for an Actor
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It is possible to require a certain type of message queue for a certain type of actor
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by having that actor extend the parameterized trait `RequiresMessageQueue`. Here is
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by having that actor @scala[extend]@java[implement] the parameterized @scala[trait]@java[interface] `RequiresMessageQueue`. Here is
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an example:
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@@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #required-mailbox-class }
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Scala
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: @@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #required-mailbox-class }
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The type parameter to the `RequiresMessageQueue` trait needs to be mapped to a mailbox in
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Java
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: @@snip [MyBoundedActor.java]($code$/java/jdocs/actor/MyBoundedActor.java) { #my-bounded-untyped-actor }
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The type parameter to the `RequiresMessageQueue` @scala[trait]@java[interface] needs to be mapped to a mailbox in
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configuration like this:
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@@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #bounded-mailbox-config #required-mailbox-config }
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@ -26,7 +30,7 @@ a dispatcher with a specified mailbox type, then that will override this mapping
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@@@ note
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The type of the queue in the mailbox created for an actor will be checked against the required type in the
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trait and if the queue doesn't implement the required type then actor creation will fail.
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@scala[trait]@java[interface] and if the queue doesn't implement the required type then actor creation will fail.
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@@@
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@ -181,7 +185,11 @@ The following mailboxes should only be used with zero `mailbox-push-timeout-time
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How to create a PriorityMailbox:
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@@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #prio-mailbox }
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Scala
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: @@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #prio-mailbox }
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Java
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: @@snip [DispatcherDocTest.java]($code$/java/jdocs/dispatcher/DispatcherDocTest.java) { #prio-mailbox }
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And then add it to the configuration:
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@ -189,19 +197,35 @@ And then add it to the configuration:
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And then an example on how you would use it:
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@@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #prio-dispatcher }
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Scala
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: @@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #prio-dispatcher }
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Java
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: @@snip [DispatcherDocTest.java]($code$/java/jdocs/dispatcher/DispatcherDocTest.java) { #prio-dispatcher }
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It is also possible to configure a mailbox type directly like this:
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@@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #prio-mailbox-config #mailbox-deployment-config }
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Scala
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: @@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #prio-mailbox-config #mailbox-deployment-config }
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Java
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: @@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #prio-mailbox-config-java #mailbox-deployment-config }
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And then use it either from deployment like this:
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@@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #defining-mailbox-in-config }
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Scala
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: @@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #defining-mailbox-in-config }
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Java
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: @@snip [DispatcherDocTest.java]($code$/java/jdocs/dispatcher/DispatcherDocTest.java) { #defining-mailbox-in-config }
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Or code like this:
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@@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #defining-mailbox-in-code }
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Scala
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: @@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #defining-mailbox-in-code }
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Java
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: @@snip [DispatcherDocTest.java]($code$/java/jdocs/dispatcher/DispatcherDocTest.java) { #defining-mailbox-in-code }
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### ControlAwareMailbox
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|
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@ -214,17 +238,36 @@ It can be configured like this:
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Control messages need to extend the `ControlMessage` trait:
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@@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #control-aware-mailbox-messages }
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Scala
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: @@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #control-aware-mailbox-messages }
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Java
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: @@snip [DispatcherDocTest.java]($code$/java/jdocs/dispatcher/DispatcherDocTest.java) { #control-aware-mailbox-messages }
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And then an example on how you would use it:
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@@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #control-aware-dispatcher }
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Scala
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: @@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #control-aware-dispatcher }
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Java
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: @@snip [DispatcherDocTest.java]($code$/java/jdocs/dispatcher/DispatcherDocTest.java) { #control-aware-dispatcher }
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## Creating your own Mailbox type
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|
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An example is worth a thousand quacks:
|
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|
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@@snip [MyUnboundedMailbox.scala]($code$/scala/docs/dispatcher/MyUnboundedMailbox.scala) { #mailbox-implementation-example }
|
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Scala
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: @@snip [MyUnboundedMailbox.scala]($code$/scala/docs/dispatcher/MyUnboundedMailbox.scala) { #mailbox-marker-interface }
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Java
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: @@snip [MyUnboundedMessageQueueSemantics.java]($code$/java/jdocs/dispatcher/MyUnboundedMessageQueueSemantics.java) { #mailbox-marker-interface }
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Scala
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: @@snip [MyUnboundedMailbox.scala]($code$/scala/docs/dispatcher/MyUnboundedMailbox.scala) { #mailbox-implementation-example }
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Java
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: @@snip [MyUnboundedMailbox.java]($code$/java/jdocs/dispatcher/MyUnboundedMailbox.java) { #mailbox-implementation-example }
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|
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And then you just specify the FQCN of your MailboxType as the value of the "mailbox-type" in the dispatcher
|
||||
configuration, or the mailbox configuration.
|
||||
|
|
@ -247,7 +290,11 @@ You can also use the mailbox as a requirement on the dispatcher like this:
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|||
|
||||
Or by defining the requirement on your actor class like this:
|
||||
|
||||
@@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #require-mailbox-on-actor }
|
||||
Scala
|
||||
: @@snip [DispatcherDocSpec.scala]($code$/scala/docs/dispatcher/DispatcherDocSpec.scala) { #require-mailbox-on-actor }
|
||||
|
||||
Java
|
||||
: @@snip [DispatcherDocTest.java]($code$/java/jdocs/dispatcher/DispatcherDocTest.java) { #require-mailbox-on-actor }
|
||||
|
||||
## Special Semantics of `system.actorOf`
|
||||
|
||||
|
|
@ -260,12 +307,25 @@ puts those inside the reference. Until that has happened, messages sent to the
|
|||
`ActorRef` will be queued locally, and only upon swapping the real
|
||||
filling in will they be transferred into the real mailbox. Thus,
|
||||
|
||||
```scala
|
||||
val props: Props = ...
|
||||
// this actor uses MyCustomMailbox, which is assumed to be a singleton
|
||||
system.actorOf(props.withDispatcher("myCustomMailbox")) ! "bang"
|
||||
assert(MyCustomMailbox.instance.getLastEnqueuedMessage == "bang")
|
||||
```
|
||||
Scala
|
||||
: @@@vars
|
||||
```scala
|
||||
val props: Props = ...
|
||||
// this actor uses MyCustomMailbox, which is assumed to be a singleton
|
||||
system.actorOf(props.withDispatcher("myCustomMailbox")) ! "bang"
|
||||
assert(MyCustomMailbox.instance.getLastEnqueuedMessage == "bang")
|
||||
```
|
||||
@@@
|
||||
|
||||
Java
|
||||
: @@@vars
|
||||
```java
|
||||
final Props props = ...
|
||||
// this actor uses MyCustomMailbox, which is assumed to be a singleton
|
||||
system.actorOf(props.withDispatcher("myCustomMailbox").tell("bang", sender);
|
||||
assert(MyCustomMailbox.getInstance().getLastEnqueued().equals("bang"));
|
||||
```
|
||||
@@@
|
||||
|
||||
will probably fail; you will have to allow for some time to pass and retry the
|
||||
check à la `TestKit.awaitCond`.
|
||||
|
|
@ -4,8 +4,8 @@
|
|||
|
||||
package jdocs.dispatcher;
|
||||
|
||||
//#mailbox-implementation-example
|
||||
//#mailbox-marker-interface
|
||||
// Marker interface used for mailbox requirements mapping
|
||||
public interface MyUnboundedMessageQueueSemantics {
|
||||
}
|
||||
//#mailbox-implementation-example
|
||||
//#mailbox-marker-interface
|
||||
|
|
|
|||
|
|
@ -15,9 +15,6 @@ import com.typesafe.config.Config
|
|||
import java.util.concurrent.ConcurrentLinkedQueue
|
||||
import scala.Option
|
||||
|
||||
// Marker trait used for mailbox requirements mapping
|
||||
trait MyUnboundedMessageQueueSemantics
|
||||
|
||||
object MyUnboundedMailbox {
|
||||
// This is the MessageQueue implementation
|
||||
class MyMessageQueue extends MessageQueue
|
||||
|
|
@ -58,3 +55,8 @@ class MyUnboundedMailbox extends MailboxType
|
|||
new MyMessageQueue()
|
||||
}
|
||||
//#mailbox-implementation-example
|
||||
|
||||
//#mailbox-marker-interface
|
||||
// Marker trait used for mailbox requirements mapping
|
||||
trait MyUnboundedMessageQueueSemantics
|
||||
//#mailbox-marker-interface
|
||||
Loading…
Add table
Add a link
Reference in a new issue