First, the reaping code has a couple of flaws. (1) there are multiple places where you do a waitpid(), (2) the reaper routine can miss some SIGCHLD's., (3) no need to set $SIG{CHLD} within REAPER

So I would suggest: 

sub REAPER 
{
   my $pid;
   while ($pid = waitpid(-1, WNOHANG) > 0)
   {
      print "Process $pid exited.\n";
      push @dead_kids, $pid;
   }
}

[download]
You are not guaranteed to get a separate SIGCHLD for each child who exits! Basically interpret SIGCHLD to mean that one or more children have exited. Use a while loop to service everybody who is ready within the signal handler. There is not going to be a "false alarm", so I took that stuff out.

Also, to "reap" a child basically means to read its exit status from the process table. The function that does this read is waitpid(). When you have this in two places, somebody may get reaped and yet not go through the reaper. I recommend letting REAPER do all of the reaping and do not call waitpid() anywhere else. Maybe this issue is why you had the "false alarm" code, a race condition? Anyway, only reap in one place and you will not miss any and won't wind up in the signal handler with somebody mysteriously disappearing!

Update: temporarily don't have access to a unix box, so can't test, but here is a suggestion..

1. I see why you had the waitpid in the parent (so see if all children have finished). You need another test, perhaps, (@dead_kids < 10) with some wait delay. I think this test will be ok in Perl without further adieu. In C I would need to protect this critical section with some procmask() voodoo. But I think that due to the way Perl >=5.8 delivers deferred signals, that this is not necessary to prevent the REAPER and parent main program from tripping over each other.

In reply to Re: Monitoring Child Process by Marshall
in thread Monitoring Child Process by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.