Thanks for reporting! On Mon, Jun 22, 2015 at 11:35 PM, Michael Frank <[email protected]> wrote:
> the current documentation appears to be incorrect, which i believe was > the source of confusion. on line 20 of the code block of the section > "Actors and shared mutable state" on page > http://doc.akka.io/docs/akka/2.3.11/general/jmm.html#jmm-shared-state it > specifically states: > > 18 // Completely safe, "self" is OK to close over > 19 // and it's an ActorRef, which is thread-safe > 20 Future { expensiveCalculation() } onComplete { f => self ! > f.value.get } > > i opened an issue for it: https://github.com/akka/akka/issues/17805 > > -Michael > > > On 06/20/15 01:45, Roland Kuhn wrote: > > Hi Frederic, > > you violate the first rule of Actors: never call *any* of their methods > from outside of their context of execution. This is true for all of them, > including context() and self(). While the result of calling self() can then > safely be shared afterwards (an ActorRef is thread-safe), the result of > context() cannot (because ActorContext is not thread-safe). > > What happens in your sample is that the Actor is destroyed due to the > Exception (that triggers a restart), so anything referencing the old Actor > instance will see a dead entity with nulls in it (in order to minimize > memory leaks in case someone does something wrong). > > Regards, > > Roland > > 19 jun 2015 kl. 02:02 skrev Frederic <[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] 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 >> >> 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$] 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'. >> > > -- > >>>>>>>>>> Read the docs: http://akka.io/docs/ > >>>>>>>>>> Check the FAQ: > http://doc.akka.io/docs/akka/current/additional/faq.html > >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user > --- > You received this message because you are subscribed to the Google Groups > "Akka User List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/akka-user. > For more options, visit https://groups.google.com/d/optout. > > > > > *Dr. Roland Kuhn* > *Akka Tech Lead* > Typesafe <http://typesafe.com/> – Reactive apps on the JVM. > twitter: @rolandkuhn > <http://twitter.com/#%21/rolandkuhn> > > -- > >>>>>>>>>> Read the docs: http://akka.io/docs/ > >>>>>>>>>> Check the FAQ: > http://doc.akka.io/docs/akka/current/additional/faq.html > >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user > --- > You received this message because you are subscribed to the Google Groups > "Akka User List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/akka-user. > For more options, visit https://groups.google.com/d/optout. > > > -- > >>>>>>>>>> Read the docs: http://akka.io/docs/ > >>>>>>>>>> Check the FAQ: > http://doc.akka.io/docs/akka/current/additional/faq.html > >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user > --- > You received this message because you are subscribed to the Google Groups > "Akka User List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/akka-user. > For more options, visit https://groups.google.com/d/optout. > -- Patrik Nordwall Typesafe <http://typesafe.com/> - Reactive apps on the JVM Twitter: @patriknw -- >>>>>>>>>> Read the docs: http://akka.io/docs/ >>>>>>>>>> Check the FAQ: >>>>>>>>>> http://doc.akka.io/docs/akka/current/additional/faq.html >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user --- You received this message because you are subscribed to the Google Groups "Akka User List" group. 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