Re^2: Ulimit makes program hang

Unfortunatelly sleeping doesn't solve the problem.

I have tested all more throughly and modified program:

#!/usr/bin/perl -w

my $x = $ARGV[0] + 1;
print STDERR "$x\n";
`./my_program $x`;
[download]

Now I ran commands:

(ulimit -u100; ./my_program)
(ulimit -u50; ./my_program)
(ulimit -u20; ./my_program)
[download]

The first one hang on 95-th iteration. The second hang on 45-th iteration. The third one hang on 15-th iteration. So wen you set maximum number or processes to N (ulimit -u<N>), then program hangs on N-5 iteration.
I want that program to fail (return nonzero code) when no processes are available...

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Re^3: Ulimit makes program hang by Hue-Bond (Priest) on Aug 13, 2008 at 14:37 UTC
`ulimit` sets the maximum number of process that your user can run. Since you are likely to be running some other processes (for instance, your shell), it comes as no surprise that there are fewer "slots" available for other processes. -- David Serrano	[reply] [d/l]
Re^4: Ulimit makes program hang by memo2005 (Initiate) on Aug 13, 2008 at 15:25 UTC
Yes -- you're right. My question is why perl hangs instead of giving up and telling user "unable to fork".	[reply]
Re^3: Ulimit makes program hang by Bloodnok (Vicar) on Aug 13, 2008 at 14:42 UTC
Hi , I strongly suspect that, if you re-insert the `sleep` before shelling out, your results will be modified since the perl process won't otherwise have enough time to complete the `print`. Have you tried the `fork`/`exec` approach ? Have you tried an even lower limit and running the program using `truss` (or is it `strace` on linux) ? As an afterthought, I do wonder if you've uncovered a bug in perl... A user level that continues to overstate my experience :-))	[reply] [d/l] [select]
Re^4: Ulimit makes program hang by memo2005 (Initiate) on Aug 13, 2008 at 15:50 UTC
After insterting `sleep` before shelling out I get exactly same results. I'm not a system programmer to analyse `strace` output...sorry. I have tried `fork` and `exec` this way: `#!/usr/bin/perl -w my $x = $ARGV[0] + 1; print STDERR "$x\n"; if (!defined($child_pid = fork())) { die "cannot fork: $!"; } elsif ($child_pid) { waitpid($child_pid, 0); } else { exec "$0 $x"; }` [download] This program never hangs -- always says `cannot fork: Resource temporarily unavailable at ./fork_wait line 7`. But I must grab output of command so I can't use this solution.	[reply] [d/l]
Re^5: Ulimit makes program hang by Bloodnok (Vicar) on Aug 13, 2008 at 16:50 UTC
...as I suspected, using the evidence of your OP and this posting, I think you've got enough to raise a perl bug against the backtick (``) operator - I think it should `die` with a similar fatal error. Section 16 of the Perl Cookbook should provide you with some background in order to progress further with capturing output from a command ... HTH , A user level that continues to overstate my experience :-))	[reply] [d/l] [select]