June 2017 - dancer-users - lists.preshweb.co.uk

How can a fork+system() Dancer app not create zombie processes?
by Shlomi Fish 29 Jun '17

29 Jun '17

Hi all! When running a simple and reduced Dancer 1 application which forks and runs perldoc -f system , I am getting many zombie processes after making requests. This does not happen with https://github.com/shlomif/shlomif-perl-snippets/blob/master/tcp-socket-ser… which does the same thing using IO::Socket and plain TCP. To reproduce, do: hg clone https://shlomif@bitbucket.org/shlomif/app-notifier cd app-notifier hg checkout zombies-processes-bug cd App-Notifier-Service/ And then run “bash run-server.bash” and in a different shell session “bash run-client.bash.” . You can run 'pstree -p' to see the zombies processes. This happens on Mageia v6 x86-64 and Fedora 25 x86-64 with perl-Dancer-1.320.200-2.mga6 . I am quoting a discussion I had on #dancer on irc.perl.org about it. Any further insights about a solution will be welcome. Regards, Shlomi Fish ``` Apr 02 16:47:21 <rindolf> Hi all! My dancer service here (run run-server.bash and then run-client.bash in the App-Notifier-Service directory and note the branch) generates many zombie processes - how can I prevent it from happening? https://bitbucket.org/shlomif/app-notifier/branch/zombies-processes-bug Apr 02 16:54:58 <racke> how do you start the dancer service? Apr 02 16:55:57 <rindolf> racke: perl -I"`pwd`/lib" bin/app.pl --port=6300 Apr 02 16:56:25 <racke> so that is Dancer 1 ? Apr 02 16:56:40 <rindolf> racke: yes, it is Apr 02 16:58:36 <racke> you start only one instance so i might not be able to handle the incoming request Apr 02 16:59:32 <rindolf> racke: it handles most requests fine Apr 02 16:59:36 <racke> better use something like plackup -s Starman --workers=5 Apr 02 17:01:13 <rindolf> racke: what do I need it for? Apr 02 17:01:38 <racke> as I explained before Apr 02 17:01:44 <racke> you need more than one instance Apr 02 17:02:33 <rindolf> racke: see https://metacpan.org/pod/App::Notifier::Service for my use case Apr 02 17:02:38 <rindolf> racke: why? Apr 02 17:03:08 <rindolf> racke: i don't need to handle moer than one request at the time Apr 02 17:03:23 <racke> hm Apr 02 17:03:30 <racke> if you think so Apr 02 17:05:01 <racke> you probably don't handle fork correctly, that is likely to cause your zombies Apr 02 17:05:27 <rindolf> racke: I followed perldoc perlipc Apr 02 17:10:42 <racke> well why not use something like IPC::RUn? Apr 02 17:16:33 <rindolf> racke: 1. I used fork+system - it is enough for my needs, 2. I provided a link to the code - did you take a look? 3. I found IPC::Run buggy when i used it in a different project Apr 02 17:17:22 <rindolf> racke: and also - this is the reduced-to-a-minimum code Apr 02 17:19:23 <racke> yeah I did take a look Apr 02 17:19:49 <rindolf> racke: ok, thanks! Apr 02 17:20:09 <racke> I am not familar with using fork so ... Apr 02 17:20:33 <racke> but it looks like it produces your army of zombies :-) Apr 02 18:01:22 <rindolf> racke: the IO-Socket-INET equivalent does not spawn any zombies - https://github.com/shlomif/shlomif-perl-snippets/blob/master/tcp-socket-ser… Apr 02 18:07:07 <rindolf> http://stackoverflow.com/questions/13614498/forking-to-run-code-in-a-child-… - there is this too ``` -- ----------------------------------------------------------------- Shlomi Fish http://www.shlomifish.org/ My Favourite FOSS - http://www.shlomifish.org/open-source/favourite/ Chuck Norris can end world hunger, but he thinks that hungry people make humanity a more challenging adversary. — http://www.shlomifish.org/humour/bits/facts/Chuck-Norris/ Please reply to list if it's a mailing list post

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Re: [dancer-users] How can a fork+system() Dancer app not create zombie processes?
by Andrew Beverley 29 Jun '17

29 Jun '17

On Thu, 29 Jun 2017 17:35:07 +1000 Nathan Bailey wrote: > > > I want to send my Dancer2 TT page as an email *and* continue to > > > generate a normal web response. > > > > > > This forking discussion seems like an excellent approach. > > > > I'm not convinced - it seems like overkill to me. > > > > How would I generate two outputs from the one process otherwise? More > specifically, how do I invoke the same route twice? Ah, I missed that bit. Nonetheless, can you not just call the template keyword directly, generate the email content and send? Then generate the page content and return that from the route handler. The template keyword doesn't actually end anything: it just produces content which normally gets returned. > Have you loaded a suitable guard module (e.g. Guard or Scope::Guard)? > > Otherwise (from memory) the application will exit before it raises an > > exception of the missing guard function. > > > > Yes, I installed Guard. I will try its debug mode to see if it tells me > more about why it's failing. Did you load it in your application as well? e.g. somewhere in your code before it's called: use Guard; Andy

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DPAE logging
by Nathan Bailey 13 Jun '17

13 Jun '17

Hi all, I'm trying to work out why my permission_denied_page_handler isn't working in Dancer2::Plugin::Auth::Extensible. However, as a separate problem I get none of DPAE's logging messages. If I write: app->log(core => "Testing 1..2..3.."); in my app, this message doesn't appear anywhere in my log files. Where should it be going/appearing? Note that this is true whether I use 'logger: File' or 'logger: LogReport' thanks, Nathan PS: Pertinent to the original problem, if I dump app, I can see that permission_denied_page_handler *has* been set to MyApp::permission_denied_page_handler but the subroutine in MyApp.pm never gets called.

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