Forum OpenACS Development: Re: Image resizing, exec and server problems

27: Re: Image resizing, exec and server problems (response to 25)

Posted by russell muetzelfeldt on 05/08/08 07:45 AM

hmmm... that number scared me, but I've just run a quick test with 20 parallel clients each making 100 requests, each of which required 20 [exec] calls to service (so 40,000 exec calls in ~10 min spread across 10 connection threads)... every single one completed successfully, all my threads are still there and accepting connections, and the nsd process hasn't grown by any significant amount... perhaps the TCL threaded fork issue has been fixed? (debian etch, kernel 2.6.22-4-amd64, tcl 8.4.12-1.1, aolserver4 4.0.10-7)

28: Re: Image resizing, exec and server problems (response to 27)

Posted by Stefan Sobernig on 05/08/08 09:41 AM

Russell!

As long as it works for you and you tested (with a minimum effort) that it scales (to whatever extent) than it is apparently fine (at least).

However, another critical thing is the kind of exec call itself (redirector, background, ...) and the code surrounding it. Malte never posted the critical exec line, at least to my knowledge.

In other words, if it works for you. Go ahead!

My option referred more to use a non-blocking variant and link it to the background delivery feature (a larger picture of design).

I agree while there are resources on comp.lang.tcl etc. that report on the threaded fork() issue, I cannot find a concise statement on the issue's state (fixed, open, unsolvable).

29: Re: Image resizing, exec and server problems (response to 28)

Posted by russell muetzelfeldt on 05/08/08 12:03 PM

as I understand it the surrounding TCL code is irrelevant, as is whether the fork is the result of calling [exec], [open "|whatever"] or anything else... the problem is TCL doesn't/didn't implement pthread_atfork, so threads might lock up any time a new process is fork()/exec()'d by TCL... I understand what you're talking about with running the event loop to avoid blocking, but we don't have any problem with long-running children blocking IO for other threads so it's not related to the problem I thought I might be facing... looks interesting though...

30: Re: Image resizing, exec and server problems (response to 29)

Posted by Gustaf Neumann on 05/08/08 02:32 PM

russell, have you considered using tclmagic?
it allows image resizing, there are no forks involved, since it can be loaded into aolserver

Short intro: http://wiki.tcl.tk/9775