On 05.02.15 16:38, Roland Kuhn wrote:
Hi Martin,
I’m hesitant to do this since this method is not “safe” from a message
ordering standpoint: if the unstashed message ends up being re-stashed
(due to faulty logic) then it will go from the head to the tail of the
stash. It does seem like an “expert feature” to me.
As long as the documentation is clear about that, why not just let the
user decide if it should be used or not? You have potential re-ordering
issues also in another place of Akka's public API: AtLeastOnceDelivery,
for example.
The context I considered this is (very recently) is Akka Typed: I have
not yet figured out how or even if to provide this feature. The only
difference between The Stash and a normal linear buffer within the
actor itself is that the former is retained across a restart while the
latter is not. Since the Actor obviously was faulty (otherwise there
would be no restart), how much can we trust the stash? If the stashing
and the function of the Actor are not related, then we can easily
express these two in separate Actors, with the stash being the parent
of the real recipient.
But in this case the child has to pull the messages from the parent's
internal buffer when ready for the next message. Otherwise, you'd
introduce ordering issues again. We had this pattern implemented in
early development stages of akka-persistence but then switched to
unstash() for efficiency reasons (and because it was a lot simpler).
Furthermore, I don't think my use case is that uncommon:
- actor state machine with states s1 and s2
- if in s1, process message and switch to s2
- if in s2, stash message(s) and do some async processing
- if async processing completes, switch back to s1 and process next message
Using unstashAll() in the last step copies the all stashed messages
back, only for processing the next one and redundantly stashing the
others -> this is O(n*n) where n = number of messages in the mailbox.
This is very painful for a large number of messages in the mailbox.
Making unstash() public would be a simple and IMO clean solution to this
problem.
Regards,
Roland
5 feb 2015 kl. 16:29 skrev Martin Krasser <[email protected]
<mailto:[email protected]>>:
Hi,
does anything speak against making unstash()
<https://github.com/akka/akka/blob/v2.3.9/akka-actor/src/main/scala/akka/actor/Stash.scala#L186>
public (currently private[akka])? In my use case, it would help me to
avoid redundantly moving messages between the stash and the actor
mailbox using stash()/unstashAll().
Thanks,
Martin
--
Martin Krasser
blog:http://krasserm.github.io
code:http://github.com/krasserm
twitter:http://twitter.com/mrt1nz
--
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*Dr. Roland Kuhn*
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Typesafe <http://typesafe.com/> – Reactive apps on the JVM.
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Martin Krasser
blog: http://krasserm.github.io
code: http://github.com/krasserm
twitter: http://twitter.com/mrt1nz
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