[99s-extend] Cowboy handler linked processes

[Adrian Roe]

That would be perfect!  Do you want me to make the change and issue a pull request?  

--  
Dr Adrian Roe
Director


On Thursday, 18 July 2013 at 11:36, Loïc Hoguin wrote:

> I don't think the problem is that the handler is reused, we don't reuse  
> them if there's an error. However we do catch errors to print them in  
> the logs, and then the process stops normally. If you link without  
> trap_exit you receive a normal exit signal which is ignored and doesn't  
> kill your process. I suppose we should throw an exit signal when we got  
> an error, after logging everything, instead of stopping normally.
>  
> On 07/18/2013 12:31 PM, Adrian Roe wrote:
> > My issue is the other way round. My handler crashes - and terminate
> > gets called, but the linked process is NOT stopped (unless I stop it in
> > terminate having stashed any processes I need to stop in the process
> > dictionary - this is what I'm currently doing, but yuck!)
> >  
> > . My question is whether it wouldn't be better to no re-use the handler
> > process that has crashed and replace it so that handler's can use the
> > canonical erlang way of stopping related processes rather than having to
> > do it by hand.
> >  
> > Obviously if the handler does not crash there's no need to kill the
> > process, so the current efficiency saving works in the "normal" case/
> >  
> > --
> > Dr Adrian Roe
> > Director
> >  
> > On Thursday, 18 July 2013 at 11:20, Loïc Hoguin wrote:
> >  
> > > I don't know what happens but there's two things I know:
> > >  
> > > * Handlers don't trap_exit, so if the linked process crashes, they
> > > crash too
> > > * If the handler crashes, we close the connection and stop the
> > > handler; if not this is a bug
> > >  
> > > After your log message the handler should stop unless there's a bug
> > > somewhere.
> > >  
> > > On 07/18/2013 12:15 PM, Adrian Roe wrote:
> > > > We have been using spawn_linked workers to handle tasks that live for
> > > > the lifetime of a single HTTP request
> > > >  
> > > > Although in the cowboy guide it is clear that Cowboy can use "One
> > > > Process of Many Requests" I am surprised that this is the case even if
> > > > the handler crashes. For example, our use case is to copy a large file
> > > > to the server over HTTP where a worker process relays the file contents
> > > > to long term storage. The worker process is spawn_linked from the HTTP
> > > > handler and (for our use case) should die if the handler stops.
> > > >  
> > > > If the client stops the upload (for example by browsing away, or losing
> > > > connectivity) we correctly receive an error (see sample Lager trace
> > > > below), but what we are seeing is that spawn_linked processes are NOT
> > > > being killed.
> > > >  
> > > > Is this intended behaviour - I accept it makes sense to reuse the
> > > > processes but should this continue to be the case even if the previous
> > > > use of the process crashed? If it is intended behaviour I think the
> > > > docs should highlight this as we've been leaking processes for some time
> > > > now, but I've always seen it as erlang's job to look after related
> > > > process trees in the event of error. Our current workaround is to hold
> > > > a list of linked processes in process storage and then kill them in the
> > > > terminate handler which is ugly in the extreme!! We don't know the PIDS
> > > > of the linked processes until it is too late to return State to Cowboy
> > > > (i.e. we are already in our handle code)...
> > > >  
> > > > Kind regards
> > > >  
> > > > Adrian
> > > >  
> > > > 16:09:32.347 [info] Trailer upload failed with reason
> > > > {case_clause,{error,closed}}
> > > > 16:09:32.348 [error] ** Cowboy handler upload_trailer_resource
> > > > terminating in handle/2
> > > > for the reason error:{case_clause,{error,closed}}
> > > > ** Handler state was {state,undefined,0,undefined,undefined,undefined}
> > > > ** Request was
> > > > [{socket,#Port<0.11230>},{transport,ranch_tcp},{connection,keepalive},{pid,<0.1987.0>},{method,<<"POST">>},{version,'HTTP/1.1'},{peer,{{84,92,32,116},64136}},{host,<<"54.225.117.108">>},{host_info,undefined},{port,8000},{path,<<"/upload_trailer">>},{path_info,undef
> > > > ined},{qs,<<"name=linux-7.4.21.zip&size=54015414">>},{qs_vals,undefined},{bindings,[]},{headers,[{<<"host">>,<<"54.225.117.108:8000">>},{<<"connection">>,<<"keep-alive">>},{<<"content-length">>,<<"54015414">>},{<<"origin">>,<<"http://54.225.117.108:8000">>},{<<"user-agent">>,<<"M
> > > > ozilla/5.0 (Macintosh; Intel Mac OS X 10_8_4) AppleWebKit/537.36 (KHTML,
> > > > like Gecko) Chrome/28.0.1500.71
> > > > Safari/537.36">>},{<<"content-type">>,<<>>},{<<"accept">>,<<"*/*">>},{<<"referer">>,<<"http://54.225.117.108:8000/">>},{<<"accept-encoding">>,<<"gzip,deflate,sdch">>},{<<"acce
> > > > pt-language">>,<<"en-US,en;q=0.8">>},{<<"cookie">>,<<"__jwpusr=cbc133d7-1b49-443c-8a13-364660cc93e5;
> > > > id3as_manager=f4803c004d71dde3b64394f6e6f44faa54970e93">>}]},{p_headers,[{<<"connection">>,[<<"keep-alive">>]}]},{cookies,undefined},{meta,[]},{body_state,waiting},{multipart,unde
> > > > fined},{buffer,<<>>},{resp_compress,true},{resp_state,waiting},{resp_headers,[]},{resp_body,<<>>},{onresponse,undefined}]
> > > > ** Stacktrace:
> > > > [{i_cowboy,stream_body,0,[{file,"src/i_cowboy.erl"},{line,76}]},{upload_trailer_resource,stream_upload_file,4,[{file,"src/endpoints/upload_trailer_resource.erl"},{line,247}]},{upload_trailer_resource,upload_file,1,[{file,"src/endpoints/upload_trailer_resource.erl"}
> > > > ,{line,237}]},{upload_trailer_resource,head_or_post,1,[{file,"src/endpoints/upload_trailer_resource.erl"},{line,202}]},{upload_trailer_resource,sequence,2,[{file,"src/endpoints/upload_trailer_resource.erl"},{line,106}]},{upload_trailer_resource,process_request,1,[{file,"src/endpo
> > > > ints/upload_trailer_resource.erl"},{line,212}]},{i_cowboy,do,3,[{file,"src/i_cowboy.erl"},{line,29}]},{cowboy_handler,handler_handle,4,[{file,"src/cowboy_handler.erl"},{line,119}]}]
> > > >  
> > > >  
> > > > --
> > > > Dr Adrian Roe
> > > > Director
> > > >  
> > > >  
> > > >  
> > > > _______________________________________________
> > > > Extend mailing list
> > > > Extend at lists.ninenines.eu <mailto:Extend at lists.ninenines.eu>
> > > > http://lists.ninenines.eu:81/listinfo/extend
> > > >  
> > >  
> > >  
> > >  
> > > --
> > > Loïc Hoguin
> > > Erlang Cowboy
> > > Nine Nines
> > > http://ninenines.eu
> > >  
> >  
> >  
>  
>  
>  
> --  
> Loïc Hoguin
> Erlang Cowboy
> Nine Nines
> http://ninenines.eu
>  
>  


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ninenines.eu/archives/extend/attachments/20130718/79e075b8/attachment.html>