[erlang-questions] msg mailbox and gen_svr shutdown

[Bob Ippolito]

Yes, it is documented that request processes continue after you stop the
listener. This is incorrect.

On Sunday, May 13, 2012, Anthony Ramine wrote:

> Paweł, from what I gather your supervisor waits 1 ms before killing its
> children; I think it's pretty normal that some messages are left
> unprocessed.
> Bob, cowboy_requests_sup' shutdown strategy is brutal_kill, is it
> documented somewhere that Cowboy waits before killing requests' processes?
>
> Regards,
>
> --
> Anthony Ramine
>
>
>
>
> Le 10 mai 2012 à 22:37, Bob Ippolito a écrit :
>
> I had the same problem with Cowboy recently, really ought to file an issue
> to at least fix the docs for that.
>
> For my app I wanted to implement a graceful shutdown that stopped
> accepting new connections but allowed existing requests to finish. The
> waiting part I implemented by adding a gproc local property to the workers
> that I wanted to wait for and then monitoring them.
>
> Looks like this:
> https://gist.github.com/2655724
>
> On Thu, May 10, 2012 at 2:53 AM, Paweł Peregud <paulperegud@REDACTED<javascript:_e({}, 'cvml', 'paulperegud@REDACTED');>
> > wrote:
>
>> I was having fun with supervisors yesterday (Cowboy seems to fail to
>> fulfill the promise of not killing request processes after listener
>> removal) and I have an example. I've only investigated the case when
>> supervisor is killed, so YMMV. Example code is attached. You may modify it
>> to check the behavior in your case.
>>
>> Start supervisor tree with exp_sup_sup:start_link(). Execute test with
>> exp_sup_sup:test() and exp_sup_sup:test_simple().
>>
>> In case of dying supervisor the answer is "no, it does not".
>>
>> When supervisor dies, your process is killed as via link mechanism, so it
>> may leave some unprocessed messages in inbox. To make sure that every
>> delivered message is served, you need to add process_flag(trap_exit, true).
>> Messages that are sent after the moment when supervisor dies are not
>> processed.
>>
>> Best regards,
>>
>> Paul.
>>
>> On May 9, 2012 11:06 AM, "Andy Richards" <
>> andy.richards.iit@REDACTED <javascript:_e({}, 'cvml',
>> 'andy.richards.iit@REDACTED');>> wrote:
>>
>>> Hi,
>>>
>>> I can't seem to see any confirmation in the documentation so was
>>> wondering if anyone could confirm if messages are still sent to a
>>> supervised gen_svr following a shutdown message?
>>>
>>> If so how do I cleanly shutdown my gen_svr without loosing messages? I
>>> read in the supervisor child spec that a shutdown can be set to infinity
>>> which i hoped would allow me to process the msg's in my mailbox but if I do
>>> this will my module continue to receive messages from other processes? Is
>>> my approach flawed and if so what other ways are there to cleanly shutting
>>> down my gen_svr without loosing messages?
>>>
>>> Many thanks,
>>>
>>> Andy.
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>>
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