19 jun 2015 kl. 02:02 skrev Frederic <[email protected]
<mailto:[email protected]>>:
There's more... as context is also null in the Future's callback,
anything using context won't work, see below for an updated example
using the Akka's scheduler and dispatcher:
import akka.actor._
import scala.concurrent._
import scala.concurrent.duration._
case class Done(s: String)
case object Greet
case class Complete(p: Promise[Unit])
class Greeter extends Actor {
import context.dispatcher
def receive = {
case Done(s) => println(s"Done($s) (system still running)!")
case Complete(p) => p.success(())
case Greet =>
val p = Promise[Unit]()
val saveMyself = self
val sched = context.system.scheduler
val disp = context.dispatcher
p.future onComplete {
case _ =>
println(s"self is $self")
println(s"self is expexted to be $saveMyself")
// cannot use self to send a message, need to close on self
self ! Done("Send using self")
saveMyself ! Done("Send using saveMyself")
// are we supposed to avoid using context here?
println(s"context is $context") // outputs: context is null
// is this meant to work?
// context.system.scheduler.scheduleOnce(1.millisecond,
saveMyself, Done)
// will fail because we can't get the scheduler as context
is null
try { context.system.scheduler.scheduleOnce(1.millisecond,
saveMyself, Done("scheduler 1")) } catch { case e => println(e) }
// The following will still fail because implicit
dispatcher is context.dispatcher and context is null
try { sched.scheduleOnce(1.millisecond, saveMyself,
Done("scheduler 2")) } catch { case e => println(e) }
// that will work...
sched.scheduleOnce(1.millisecond, saveMyself, Done("scheduler
3"))(disp, saveMyself)
}
self ! Complete(p)
throw new Exception("Messing with onComplete callback, self
will be dead letters")
}
}
object HelloAkkaScala extends App {
val system = ActorSystem("helloakka")
val greeter = system.actorOf(Props[Greeter], "greeter")
greeter ! Greet
}
Program output :
Running HelloAkkaScala
self is Actor[akka://helloakka/deadLetters]
[ERROR] [06/18/2015 16:47:50.464]
[helloakka-akka.actor.default-dispatcher-3]
[akka://helloakka/user/greeter] Messing with onComplete callback,
self will be dead letters
java.lang.Exception: Messing with onComplete callback, self will be
dead letters
at Greeter$anonfun$receive$1.applyOrElse(HelloAkkaScala.scala:40)
at akka.actor.Actor$class.aroundReceive(Actor.scala:467)
at Greeter.aroundReceive(HelloAkkaScala.scala:9)
at akka.actor.ActorCell.receiveMessage(ActorCell.scala:516)
at akka.actor.ActorCell.invoke(ActorCell.scala:487)
at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:238)
at akka.dispatch.Mailbox.run(Mailbox.scala:220)
at
akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(AbstractDispatcher.scala:397)
at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
at
scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
at
scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
at
scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)
self is expexted to be Actor[akka://helloakka/user/greeter#-1327535750]
context is null
java.lang.NullPointerException
java.lang.NullPointerException
Done(Send using saveMyself) (system still running)!
[INFO] [06/18/2015 16:47:50.480]
[helloakka-akka.actor.default-dispatcher-4]
[akka://helloakka/deadLetters] Message [Done] from
Actor[akka://helloakka/deadLetters] to
Actor[akka://helloakka/deadLetters
<akka://helloakka/deadLetters]%20Message%20[Done]%20from%20Actor[akka://helloakka/deadLetters]%20to%20Actor[akka://helloakka/deadLetters>]
was not delivered. [1] dead letters encountered. This logging can be
turned off or adjusted with configuration settings
'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
Done(scheduler 3) (system still running)!
On Thursday, June 18, 2015 at 2:37:35 PM UTC-7, Frederic wrote:
Hello,
I found a quite specific case involving Actors, Future callbacks
and exceptions where self becomes deadLetters.
I have the feeling I'm using self the way it is meant to be used,
as described here:
http://doc.akka.io/docs/akka/2.3.11/general/jmm.html#jmm-shared-state
<http://doc.akka.io/docs/akka/2.3.11/general/jmm.html#jmm-shared-state>
Am I doing something wrong or is it a bug?
Please see code and output below to reproduce/illustrate the issue.
Thanks, Fred
import akka.actor._
import scala.concurrent._
case object Done
case object Greet
case class Complete(p: Promise[Unit])
class Greeter extends Actor {
import context.dispatcher
def receive = {
case Done => println("Done (system still running)!")
case Complete(p) => p.success(())
case Greet =>
val p = Promise[Unit]()
val saveMyself = self
p.future onComplete {
case _ =>
println(s"self is $self")
println(s"self is expexted to be $saveMyself")
// cannot use self to send a message, bug?
self ! Done
saveMyself ! Done
}
self ! Complete(p)
throw new Exception("Messing with onComplete callback, self
will be dead letters")
}
}
object HelloAkkaScala extends App {
val system = ActorSystem("helloakka")
val greeter = system.actorOf(Props[Greeter], "greeter")
greeter ! Greet
}
Program output :
Running HelloAkkaScala
self is Actor[akka://helloakka/deadLetters]
[ERROR] [06/18/2015 14:25:41.510]
[helloakka-akka.actor.default-dispatcher-4]
[akka://helloakka/user/greeter] Messing with onComplete callback,
self will be dead letters
java.lang.Exception: Messing with onComplete callback, self will
be dead letters
at Greeter$anonfun$receive$1.applyOrElse(HelloAkkaScala.scala:27)
at akka.actor.Actor$class.aroundReceive(Actor.scala:467)
at Greeter.aroundReceive(HelloAkkaScala.scala:8)
at akka.actor.ActorCell.receiveMessage(ActorCell.scala:516)
at akka.actor.ActorCell.invoke(ActorCell.scala:487)
at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:238)
at akka.dispatch.Mailbox.run(Mailbox.scala:220)
at
akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(AbstractDispatcher.scala:397)
at
scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
at
scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
at
scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
at
scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)
self is expexted to be Actor[akka://helloakka/user/greeter#990239115]
Done (system still running)!
[INFO] [06/18/2015 14:25:41.516]
[helloakka-akka.actor.default-dispatcher-3]
[akka://helloakka/deadLetters] Message [Done$
<akka://helloakka/deadLetters]%20Message%20[Done$>] from
Actor[akka://helloakka/deadLetters] to
Actor[akka://helloakka/deadLetters] was not delivered. [1] dead
letters encountered. This logging can be turned off or adjusted
with configuration settings 'akka.log-dead-letters' and
'akka.log-dead-letters-during-shutdown'.
--
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>>>>>>>>>> Check the FAQ:
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