Hmm, I guess I wasn't very clear... What I was trying to say is, let's say
I have something like this:
preStart {
allocate resource
something that can fail
}
I can wrap the part that can fail with a try catch, and release the
resource that was allocated. Because I am still in preStart I have the
context of what was and wasn't initialized. But if preStart finished
successfully, then I know for sure all the resources were acquired and have
to be released.
Granted, this isn't the most elegant code (takes me back to my C days, all
that's missing are goto's), but I really dislike the double-failure
solution.
Tal
On Thursday, March 31, 2016 at 4:23:19 PM UTC+3, drewhk wrote:
>
>
>
> On Thu, Mar 31, 2016 at 3:10 PM, Tal Pressman <kir...@gmail.com
> <javascript:>> wrote:
>
>>
>> Here's my (unimportant and unsolicited ^_^) opinion.
>> I think this should be left as is for a couple of reasons.
>> 1. In the case you mentioned where a file is opened in the c'tor,
>>
>
> But what I was arguing is if you allocate the file in preStart(). We
> cannot do anything with ctor failures.
>
>
>> the file could have been opened during preStart. That way if you allocate
>> the resource, you will get to postStop
>>
>
> But this is exactly what is not true here. If preStart fails, you don't
> get to postStop.
>
> Basically there is no contention on that once an actor is considered
> running, postStop should be called. The contention is when should an actor
> considered to be running, just before the invocation of preStart, of after
> the successful invocation of preStart.
>
>
>> , and if you fail in preStart you haven't allocated resources (or you
>> know how far along the initialization you are so you can clean up the
>> resources that were actually allocated).
>> 2. I generally think of preStart and postStop as being associated, like a
>> constructor and destructor (in languages that have them). In such cases, if
>> the constructor fails the destructor isn't called, and I think this case is
>> similar.
>>
>
> Interesting, for me preStart is being associated in my head in a
> completely different way: if preStart has been called, then postStop will
> be called, too, independently of exceptions thrown.
>
>
>> 3. And finally, of course, there's the backwards-compatibility issue that
>> was already mentioned here. I doubt it'll cause many issues, but the ones
>> it will cause will probably be fairly hard to detect (most projects don't
>> have tests for every object failing initialization).
>>
>
> This wouldn't be in a minor anyway as we discussed before, and majors can
> and do break semantics from time to time.
>
> Anyway, seems like apart from the original poster and me, noone is
> interested in this change. Stream stages do call postStop even after
> preStart failures though, so be aware of it.
>
> Also, consider that after an actor restart postRestart() is called, which
> will call preStart(), which, if fails will cause postStop to be called if
> the actor is stopped - unlike the normal startup scenario. This is
> inconsistent in a sense.
>
>
>>
>> Tal
>>
>>
>> On Thursday, March 31, 2016 at 3:50:00 PM UTC+3, drewhk wrote:
>>>
>>> That is an orthogonal concern in my eyes. The following options are
>>> possible now
>>> - init fails
>>> - init; preStart fails
>>> - init; preStart; postStop (fails)?
>>>
>>> The above contract is basically: "If any initialization fails, postStop
>>> is never called"
>>>
>>> It can be changed to
>>> - init fails
>>> - init; preStart (fails)?; postStop (fails)?
>>>
>>> The above contract is basically: "If initialization succeeds, preStart
>>> and postStop are attempted to be called eventually, independently of thrown
>>> exceptions"
>>>
>>> I proposed the second as it makes postStop a new line of defense which
>>> it hasn't been before. For example stream stages *do* attempt to call
>>> postStop even if preStart throws.
>>>
>>> -Endre
>>>
>>>
>>>
>>> On Thu, Mar 31, 2016 at 2:41 PM, Viktor Klang <viktor...@gmail.com>
>>> wrote:
>>>
>>>> PostStop would never be called if the constructor fails. Which could be
>>>> said to be similar to preStart?
>>>>
>>>> --
>>>> Cheers,
>>>> √
>>>> On Mar 31, 2016 2:39 PM, "Endre Varga" <endre...@lightbend.com> wrote:
>>>>
>>>>
>>>>>
>>>>> On Thu, Mar 31, 2016 at 2:36 PM, Guido Medina <oxy...@gmail.com>
>>>>> wrote:
>>>>>
>>>>>> it gets worse if I failed starting "b" because now "a" is started
>>>>>> and it won't be stopped,
>>>>>>
>>>>>
>>>>> I don't understand this question. If we failed starting "b" then it
>>>>> will not be running, this is not changed by calling postStop() on the
>>>>> retreat before nulling out the actor.
>>>>>
>>>>>
>>>>>> such cases IMHO should be handled by the user
>>>>>>
>>>>> and
>>>>>> instead just stick to the contract which is, "stop if was started"
>>>>>> which will lead to less
>>>>>>
>>>>>
>>>>> The contract will be here just as simple first preStart and eventually
>>>>> postStop will be attempted to be called, after which the actor is
>>>>> GC-able.
>>>>> This is also a simple contract.
>>>>>
>>>>>
>>>>>> confusion and easier to maintain the exceptional cases.
>>>>>>
>>>>>>
>>>>>> On Thursday, March 31, 2016 at 1:23:39 PM UTC+1, Guido Medina wrote:
>>>>>>>
>>>>>>> so, say:
>>>>>>>
>>>>>>> Object a = null, Object b = null;
>>>>>>>
>>>>>>> preStart():
>>>>>>>
>>>>>>> a = new something(); a.start(); *<= say I failed here.*
>>>>>>> b = new somethingElse(); b start();
>>>>>>>
>>>>>>> postStop():
>>>>>>>
>>>>>>> b.stop(); boom NPE.
>>>>>>> a.stop();
>>>>>>>
>>>>>>> That's why the word transaction exist right? A unit is considered
>>>>>>> started or valid of all its parts are valid and started...
>>>>>>> But go ahead, make legacy code life miserable...the decision is
>>>>>>> yours.
>>>>>>>
>>>>>>> Try catch is there for a reason but somehow magic exists.
>>>>>>>
>>>>>>> Guido.
>>>>>>>
>>>>>>> On Thursday, March 31, 2016 at 1:15:27 PM UTC+1, drewhk wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> On Thu, Mar 31, 2016 at 2:10 PM, Guido Medina <oxy...@gmail.com>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> I haven't seen any system stopping something consciously that it
>>>>>>>>> was unable to start, the created instance is just an instance like
>>>>>>>>> another
>>>>>>>>> other object which will be GCed.
>>>>>>>>>
>>>>>>>>
>>>>>>>> I don't agree, you might have opened a file or socket in the
>>>>>>>> constructor or parts of preStart() before the exception.
>>>>>>>>
>>>>>>>>
>>>>>>>>> If you look at it from a state machine perspective Status: CREATED
>>>>>>>>> => CALL START (or preStart don't worry about details) => Status:
>>>>>>>>> Started
>>>>>>>>>
>>>>>>>>> It is more destructive to call postStop if it didn't actually
>>>>>>>>> started because then you will get NPE for stopping things that are
>>>>>>>>> part of
>>>>>>>>> the actor that weren't instantiated.
>>>>>>>>>
>>>>>>>> Now I have to protect my code from Akka calling postStop...see my
>>>>>>>>> point?
>>>>>>>>>
>>>>>>>>
>>>>>>>> Nope, Akka should just swallow the double-fault at that point. I
>>>>>>>> still think it should at least attempt to call postStop() to mitigate
>>>>>>>> resource leaks.
>>>>>>>>
>>>>>>>> -Endre
>>>>>>>>
>>>>>>>>
>>>>>>>>>
>>>>>>>>> Guido.
>>>>>>>>>
>>>>>>>>> On Thursday, March 31, 2016 at 9:19:15 AM UTC+1, drewhk wrote:
>>>>>>>>>>
>>>>>>>>>> That description suits me ;)
>>>>>>>>>>
>>>>>>>>>> On Thu, Mar 31, 2016 at 10:18 AM, Patrik Nordwall <
>>>>>>>>>> patrik....@gmail.com> wrote:
>>>>>>>>>>
>>>>>>>>>>> From the source: "Only change this if you're very confident and
>>>>>>>>>>> lucky" :-)
>>>>>>>>>>>
>>>>>>>>>>> On Thu, Mar 31, 2016 at 9:30 AM, Endre Varga <
>>>>>>>>>>> endre...@lightbend.com> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> Shouldn't we all postStop there if preStart has been at least
>>>>>>>>>>>> invoked (i.e. there is already an instance)? It does not seem to
>>>>>>>>>>>> be hard,
>>>>>>>>>>>> just shuffling that code a bit around (famous last words?).
>>>>>>>>>>>>
>>>>>>>>>>>> On Thu, Mar 31, 2016 at 9:25 AM, Patrik Nordwall <
>>>>>>>>>>>> patrik....@gmail.com> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>> I think that is how it is implemented. Exception from preStart
>>>>>>>>>>>>> results in clearing the actor field and
>>>>>>>>>>>>> throwing ActorInitializationException:
>>>>>>>>>>>>>
>>>>>>>>>>>>> https://github.com/akka/akka/blob/master/akka-actor/src/main/scala/akka/actor/ActorCell.scala#L599
>>>>>>>>>>>>>
>>>>>>>>>>>>> Default supervision will result in stop, but postStop is not
>>>>>>>>>>>>> called because the actor field was cleared:
>>>>>>>>>>>>> https://github.com/akka/akka/blob/master/akka-actor/src/main/scala/akka/actor/dungeon/FaultHandling.scala#L210
>>>>>>>>>>>>>
>>>>>>>>>>>>> On Wed, Mar 30, 2016 at 10:59 AM, Endre Varga <
>>>>>>>>>>>>> endre...@lightbend.com> wrote:
>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> On Sun, Mar 27, 2016 at 5:52 PM, Stanislav Savulchik <
>>>>>>>>>>>>>> s.sav...@gmail.com> wrote:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Hi, everyone!
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> I've discovered that Actor's postStop method doesn't get
>>>>>>>>>>>>>>> invoked if exception occurs during actor initialization via
>>>>>>>>>>>>>>> preStart
>>>>>>>>>>>>>>> method. Does anyone know if it is the correct behavior? I
>>>>>>>>>>>>>>> expected that the
>>>>>>>>>>>>>>> failed actor could close some resources in postStop.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Do you have a reproducer for this? I would also expect
>>>>>>>>>>>>>> postStop to be at least attempted to be called.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> P.S. The behavior differs when a failure occurs during
>>>>>>>>>>>>>>> regular vs. system message processing and supervisor decides to
>>>>>>>>>>>>>>> Stop the
>>>>>>>>>>>>>>> failed child. It seems inconsistent to me.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> What do you mean here? Can you provide a small example to
>>>>>>>>>>>>>> show this?
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> --
>>>>>>>>>>>>>>> >>>>>>>>>> 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
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>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> --
>>>>>>>>>>>>>> >>>>>>>>>> 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
>>>>>>>>>>>>>> ---
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>>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> --
>>>>>>>>>>>>>
>>>>>>>>>>>>> Patrik Nordwall
>>>>>>>>>>>>> Akka Tech Lead
>>>>>>>>>>>>> Lightbend <http://www.lightbend.com/> - Reactive apps on the
>>>>>>>>>>>>> JVM
>>>>>>>>>>>>> Twitter: @patriknw
>>>>>>>>>>>>>
>>>>>>>>>>>>> [image: Lightbend] <http://www.lightbend.com/>
>>>>>>>>>>>>>
>>>>>>>>>>>>> --
>>>>>>>>>>>>> >>>>>>>>>> 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
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>>>>>>>>>>>>> Visit this group at https://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:
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>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>>
>>>>>>>>>>> Patrik Nordwall
>>>>>>>>>>> Akka Tech Lead
>>>>>>>>>>> Lightbend <http://www.lightbend.com/> - Reactive apps on the
>>>>>>>>>>> JVM
>>>>>>>>>>> Twitter: @patriknw
>>>>>>>>>>>
>>>>>>>>>>> [image: Lightbend] <http://www.lightbend.com/>
>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>> >>>>>>>>>> Read the docs: http://akka.io/docs/
>>>>>>>>>>> >>>>>>>>>> Check the FAQ:
>>>>>>>>>>> http://doc.akka.io/docs/akka/current/additional/faq.html
>>>>>>>>>>> >>>>>>>>>> Search the archives:
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>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> --
>>>>>>>>> >>>>>>>>>> Read the docs: http://akka.io/docs/
>>>>>>>>> >>>>>>>>>> Check the FAQ:
>>>>>>>>> http://doc.akka.io/docs/akka/current/additional/faq.html
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>>>>>>>>>
>>>>>>>>
>>>>>>>> --
>>>>>> >>>>>>>>>> Read the docs: http://akka.io/docs/
>>>>>> >>>>>>>>>> Check the FAQ:
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>>>>>>
>>>>>
>>>>> --
>>>>> >>>>>>>>>> Read the docs: http://akka.io/docs/
>>>>> >>>>>>>>>> Check the FAQ:
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>>>> --
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>>>
>>> --
>> >>>>>>>>>> Read the docs: http://akka.io/docs/
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>
>
--
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