Hanging on backticks and ulimit -u100

[p5pRT]

Migrated from rt.perl.org#57908 (status was 'open')

Searchable as RT57908$

[p5pRT]

From memo2005@tlen.pl

Created by memo2005@tlen.pl

Please open a file named "my_program", and write three lines into it​:

#!/usr/bin/perl -w
print STDERR "$$\n";
`./my_program`;

Now open bash and execute command​:

(ulimit -u100; ./my_program)

This program hangs after reaching maximum number of child processes.
My system is​:

  Debian GNU/Linux, 2.6.18-iplus #1 SMP Wed Dec
  12 14​:35​:52 CET 2007 i686 GNU/Linux
  perl, v5.8.8 built for i486-linux-gnu-thread-multi

This bug was discussed here​:

http​://www.perlmonks.com/?node_id=704071

Perl Info

Flags:
    category=core
    severity=high

Site configuration information for perl v5.8.8:

Configured by Debian Project at Fri Apr 25 20:33:47 UTC 2008.

Summary of my perl5 (revision 5 version 8 subversion 8) configuration:
  Platform:
    osname=linux, osvers=2.6.24.4, archname=i486-linux-gnu-thread-multi
    uname='linux ninsei 2.6.24.4 #1 smp preempt fri apr 18 15:36:09 pdt 2008 i686 gnulinux '
    config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dcccdlflags=-fPIC -Darchname=i486-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.8 -Darchlib=/usr/lib/perl/5.8 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.8.8 -Dsitearch=/usr/local/lib/perl/5.8.8 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/man/man3 -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Uusesfio -Uusenm -Duseshrplib -Dlibperl=libperl.so.5.8.8 -Dd_dosuid -des'
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=define use5005threads=undef useithreads=define usemultiplicity=define
    useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
    use64bitint=undef use64bitall=undef uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS -DDEBIAN -fno-strict-aliasing -pipe -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS -DDEBIAN -fno-strict-aliasing -pipe -I/usr/local/include'
    ccversion='', gccversion='4.1.2 20061115 (prerelease) (Debian 4.1.1-21)', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=4, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
    perllibs=-ldl -lm -lpthread -lc -lcrypt
    libc=/lib/libc-2.3.6.so, so=so, useshrplib=true, libperl=libperl.so.5.8.8
    gnulibc_version='2.3.6'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib'

Locally applied patches:
    


@INC for perl v5.8.8:
    /etc/perl
    /usr/local/lib/perl/5.8.8
    /usr/local/share/perl/5.8.8
    /usr/lib/perl5
    /usr/share/perl5
    /usr/lib/perl/5.8
    /usr/share/perl/5.8
    /usr/local/lib/site_perl
    .


Environment for perl v5.8.8:
    HOME=/home/memo
    LANG=pl_PL
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games
    PERL_BADLANG (unset)
    SHELL=/bin/bash

[p5pRT]

From alexm@cpan.org

Note that "ulimit -u100" works on bash, but may be different in other
shells; e.g. it's "ulimit -p100" in dash (/bin/sh is dash in latest
GNU+Linux distros).

[p5pRT]

From @iabyn

On Wed, Aug 13, 2008 at 10​:08​:26AM -0700, memo2005 wrote​:

Please open a file named "my_program", and write three lines into it​:

#!/usr/bin/perl -w
print STDERR "$$\n";
`./my_program`;

Now open bash and execute command​:

(ulimit -u100; ./my_program)

This program hangs after reaching maximum number of child processes.
My system is​:

Debian GNU/Linux\, 2\.6\.18\-iplus \#1 SMP Wed Dec 
12 14​:35​:52 CET 2007 i686 GNU/Linux
perl\, v5\.8\.8 built for i486\-linux\-gnu\-thread\-multi

This bug was discussed here​:

http​://www.perlmonks.com/?node_id=704071

The behaviour appears intentional​:

util.c​:

  Perl_my_popen(pTHX_ const char *cmd, const char *mode)
  ...
  while ((pid = PerlProc_fork()) < 0) {
  if (errno != EAGAIN) {
  ....
  return NULL;
  }
  sleep(5);
  }

and has been that way since perl 3. Whether the behaviour is desirable, or
needs to be changed or documented, is another matter.

--
I before E. Except when it isn't.

[p5pRT]

The RT System itself - Status changed from 'new' to 'open'