[Stackless] Issue#24: killing tasklets during thread state cleanup

[Christian Tismer]

Yeah, I just left the ticked, went to the list, and came back ;-)

I'm pretty curious about "unbind" and what it is...

cheers - chris

On 11.06.13 11:18, Kristján Valur Jónsson wrote:
> Just thought I'd let you know that due to lack of response, this discussion Is continuing in the ticket.
> Anselm made the interesting suggestion to "unbind" a tasklet.  I like that thought.
> K
>
>> -----Original Message-----
>> From: stackless-bounces at stackless.com [mailto:stackless-
>> bounces at stackless.com] On Behalf Of Anselm Kruis
>> Sent: 4. júní 2013 12:16
>> To: The Stackless Python Mailing List
>> Subject: [Stackless] Issue#24: killing tasklets during thread state cleanup
>>
>> Hi,
>>
>> I recently proposed a modification of the behaviour of Stackless Python 2.7.
>> For details see http://www.stackless.com/ticket/24.
>>
>> Problem
>>
>> Upon end of a thread Stackless Python kills every tasklet, that belongs to the
>> thread.
>>
>> This behaviour is fine except for one case: if you pickle a tasklet and later
>> unpickle and continue the tasklet, pending finally blocks will be executed
>> twice:
>> - in the original tasklet during the processing of the TaskletExit exception
>> - in the unpickled tasklet during normal processing.
>>
>> If the tasklet is deleted prior to the end of the thread, finally blocks run only
>> once.
>>
>> This behaviour is inconsistent and can cause unexpected behaviour. We
>> need a way to ensure, that the original tasklet gets deleted without being
>> revivified.
>>
>> Proposal
>>
>> I propose to exempt a tasklet from being killed, if the tasklet is restorable
>> and not scheduled (stackless.schedule_remove() or
>> tasklet.remove() was called). Such a tasklet would silently get deleted, if its
>> reference count reaches zero.
>>
>> Alternatives
>>
>> - One could add a flag to a tasklet that marks the tasklet as being serialised
>> and skip killing based on the flag.
>>
>> - Modify tasklet.bind(callable) to allow rebinding an alive tasklet.
>> Then one could use tasklet.bind(lambda :None) to effectively disable killing.
>>
>> Open questions
>>
>> Are there any known use cases, that depend on the current behaviour? Are
>> there better alternatives?
>>
>> I'd like to discuss the general way to to solve this issue on the mailing list.
>> Once there is a consensus, we can sort out implementation details in the
>> ticket.
>>
>> Regards
>>     Anselm
>>
>> --
>>    Dipl. Phys. Anselm Kruis                       science + computing ag
>>    Senior Solution Architect                      Ingolstädter Str. 22
>>    email A.Kruis at science-computing.de             80807 München, Germany
>>    phone +49 89 356386 874  fax 737               www.science-computing.de
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