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From Arinto Murdopo <ari...@gmail.com>
Subject Re: close method in ProcessingElement
Date Mon, 06 May 2013 17:17:01 GMT
Thank you Matthieu!

Arinto
www.otnira.com


On Mon, May 6, 2013 at 12:05 PM, Matthieu Morel <matthieu@yahoo-inc.com>wrote:

>
>  On May 5, 2013, at 20:33 , Arinto Murdopo wrote:
>
>  Hi Matthieu,
>
>  I'm trying to understand some existing S4 code. So, that means, by
> calling the close() method, the PE instances are still alive, just that the
> resources that allocated to the instances are freed up. Are my statements
> correct?
>
>
>  Actually, the PE instance is removed from the cache, so it actually
> disappears from the system. It's possible to add a hook on either cache
> invalidation or in the onRemove() method to checkpoint before this happens.
>
>  In any case, if a new event comes and that it targets this PE,  a new
> instance will be created if none is found in the cache. Either recovering
> previous state, if checkpointed, or with a fresh state.
>
>
>
>  What are the normal use case for this close method to be invoked? And,
> what is "poison" event?
>
>
>  It's really a convenience method for PEs to decide to be removed from
> the system. Based on some condition or some specific message that is
> received, e.g. a "poison" message. Note that there is no delivery guarantee
> in case of failure in S4 so that should be taken into account.
>
>  Hope this helps,
>
>  Matthieu
>
>
>
>  regards,
>
>
>  Arinto
>  www.otnira.com
>
>
> On Sun, May 5, 2013 at 2:48 PM, Matthieu Morel <matthieu@yahoo-inc.com>wrote:
>
>> Hi Arinto,
>>
>>  that method is for properly cleaning up a PE instance. It could be used
>> to release resources that may be allocated within PE instances, and it
>> could be triggered by some special event (some kind of "poison" event), or
>> some other condition.
>>
>>  It can be called from user code and custom behavior for releasing
>> resources can be specified in "onRemove()" method.
>>
>>  Do you have a specific usage in mind?
>>
>>  Matthieu
>>
>>
>>  On May 4, 2013, at 17:17 , Arinto Murdopo wrote:
>>
>>   Hi all,
>>
>> What does close() method means in org.apache.s4.core.ProcessingElement
>> class?
>>
>>  The documentation<https://people.apache.org/~mmorel/apache-s4-0.6.0-incubating-doc/javadoc/org/apache/s4/core/ProcessingElement.html#close%28%29>says
nothing regarding this method.
>>
>>  best regards,
>>
>>    Arinto
>>  www.otnira.com
>>
>>
>>
>
>

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