I am writing a script that will fork a controlled number of subprocesses. Each subprocess will execute a command line via system so that I can reap the logs created by that process. It is possible for the executable to stop itself or so it seems. The problem is when the subprocess stops like this the parent also stops. I can force them to complete by sending SIGCONT to the child pid and then the parent pid. I thought that WNOHANG would keep the parent from hanging. I tried to capture the stop in both the parent and child but no luck. Any ideas how to get around this? I have read perlipc and have written other similar scripts that are working.

Included is some code that shows what I am attempting to do. It only forks one child but the real one will fork multiple. Perl 5.8.2 on AIX 5.3.

#!/usr/bin/perl
use strict;

use lib '/homegrown/lib';

use MY_Logging;
use MY_File qw(slurp);
use POSIX qw(:signal_h :errno_h :sys_wait_h);

select STDERR;
$|=1;

our ($me) = $0 =~ m/\/?([^\/]+)$/;

my %children;
my $child;

$SIG{CHLD} = \&REAPER;
sub REAPER {
  my $reaped_pid = waitpid(-1, &WNOHANG);
  if ($reaped_pid == -1) {
  }
  elsif (WIFEXITED($?)) {
    delete $children{$reaped_pid};
    print STDERR slurp("$me.$reaped_pid.log");
  }
  else {
    logMsg("False alarm on $reaped_pid");
  }
  $SIG{CHLD} = \&REAPER;
}

if ($child = fork()) {
  $children{$child} = 'TEST';
  logMsg("spawned pid $child");
}
else {
  close(STDERR);

  my $LOG = "$me.$$.log";
  open (STDERR, ">>$LOG") or dieScreaming("$LOG open failure: $!");

  select STDERR;
  $|=1;
  foreach my $host ('eidspstd01', 'eiqspstd01') {
    my $cmd = "...";

    logMsg("executing $cmd");

    my $CMD_LOG = "$me.$$.load.log";
    system("$cmd >$CMD_$LOG 2>&1");

    logLog($CMD_LOG); # pull in cmd log contents to STDERR
  }

  logMsg("completed TEST");
  close(STDERR);

  exit(0);
}

# wait for any children that may be running still
while (%children) {
  logMsg("WATING FOR: ", join(',', values %children));
  sleep(5);
}

logMsg("$me complete");

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In reply to Stopped child hangs parent by jafoba

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