среда, 30 июля 2014 г., 13:46:49 UTC+4 пользователь drewhk написал:
>
>
>
>
>>
>> Absolutely yes! But more exactly the behavior of recovery depends on
>> stream type.
>>
>> 1) When you reading from file then you have byte stream which must be
>> ordered and kill himself after exception.
>> 2) When you have stream from which you want collect elements to finite
>> Set then stream can be unordered, but must kill himself after exception.
>>
> 3) When you have stream of any linear changing state ( progress bar for
>> example) - stream must be ordered, but after exception you not must
>> killing him.
>>
>
> Killing what? If the progressbar is a Producer, and you have a map stage
> after it which throws an exception, the map will simply cancel its
> subscription to the Producer, it will not kill it -- it only propagates
> error downwards.
>
Yes, you lose your handler anyway. For example if exception will be throwed
when progressbar will be on 50% then you ever do not knows when it achieve
60%.
>
>
>> 4) And also you can have stream of state ( ping latency for example) -
>> unordered and exception do not kills him.
>>
>> Only two (stream property/flow modifiers):
>> 1) ordered / unordered
>> 2) drop after exceptions / not
>>
>> Without this properties you need to write MergeStrategy, FlattenStrategy
>> etc. Strategy depends on stream type, you not need to apply them each time
>> when you write .merge or .zip or .flatten.
>>
>> Today akka-streams has native support only (unordered + drop after
>> exception)
>>
>
> What do you mean by unordered? They are definitely ordered.
>
akka-streams does not guarantee save order of stream after join
transformers (merge, zip, flatten).
Stream will be ordered only if Flow has not such transformers. It is true.
val p = Flow(0 to 9).toProducer(materializer)
val p2 = Flow(p).filter(_%2 == 0).toProducer(materializer)
Flow(p).filter(_%2 != 0).merge(p2).fold("")(_ +
_).foreach(println).consume(materializer)
To solve that problem you need to choose applicable FlattenStrategy. But
eventually set stream type is more natively and reliable.
>
>>
>>> What would a filter emit in case of a failure? Will it drop an element?
>>> Will it emit an error marker? Also, what would filter do, if it encounters
>>> an error marker? Will it drop that? Will it emit it downstream?
>>>
>>
>> Drop an element of course - emit an marker it is same as wrap message in
>> Try - after that you got a lot of boilerplate code.
>>
>
>>
>>>
>>> And above is just one of the simpler scenarios. What would groupBy do?
>>> Which group does an error marker belong to? If it encounters an error,
>>> where should it emit that? On the master stream (the stream of groups)?
>>> All of the groups? One of the groups, then which one? Or should it open an
>>> error group?
>>>
>> What would splitWhen do? Or toFuture, especially if the stream emits only
>>> one element which fails? What would mapConcat do if it gets an error
>>> marker? What would buffer do if it is full? Drop error markers?
>>>
>>> Stream can not emit only one element if it infinite.
>>
>
> Streams can be finite or infinite.
>
Ok, if is finite stream and it not produce any element at all, what would
toFuture produce? Of course nothing. Future has no timeout. No any problems
in that case.
>
>
>> mapConcat is method which meaningless for infinite streams - that
>> supports my opinion that akka-streams is finite streams oriented.
>>
>> Or should we just drop elements silently without any error marker?
>>>
>> Yes
>>
>
>
> But wait, previously you wanted filter to emit a marker when elements are
> dropped so you do not get out of synch with zip. I am confused now.
>
Sorry about post with emitting marker, it was fast attempt to solve my
problem, forgot that please.
>
>
--
>>>>>>>>>> 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.
