Dear Monks,

I have the following problem. I have 24 subprocesses I wish to start on 24 different remote nodes computers. I can successfully do this using a perl fork command. However, for debugging purposes I wish to see the commands that the child processes are issued to start. I try and do this by issuing a simple 'print' statement with the issued command to a log file. The problem is this, I do 24 forks, yet a maximum of 18 commands are printed to the log file... I thought there should be 24 commands printed, since I do 24 forks! Even more surprising to me, is that all 24 processes still run correctly.

What is going on? Here is my forking code, you can see the 'print' statement in the 'child process' section: 

  if($phase==1) # Setup phase
    {
    # set up child signal handler
    $SIG{'CHLD'} = \&$sub;
    $|++;
    %fhlist;
    %fhlist2;
    %fhlist3;
    }
  elsif($phase==2) # Spawn the jobs phase
    {
    # Create an anonymous file handle
    $pid = fork();
    if($pid < 0 or not defined $pid)
      {
      print LOG "$#-> Can't fork! Bad kernel!";
      close LOG;
      die "$#-> Can't fork! Bad kernel!";
      }
    elsif($pid == 0)
      {
      # child process
print JUNKD "/usr/bin/rsh $proc $cmd\n";
      system("/usr/bin/rsh $proc $cmd");
      exit(0);
      }
    else
      {
      # Parent process, toss child file handle into the hash and move 
+on with
      # our lives.
      $fhlist{"$pid"} = $nt;
      $fhlist2{"$pid"} = $mc;
      $fhlist3{"$pid"} = $um;
      }  
    }
  elsif($phase==3) # Wait till the children are done phase
    {
    while(1)
      {
      @kl = keys(%fhlist);
      if($#kl >= 0)
        {
        # mo' to do...
        sleep($sleep);
        }
      else
        {
        last;
        }
      }
    }

[download]
Any ideas or suggestions would be greatly appreciated! Thanks!

In reply to Cannot print child process command during fork by whatwhat

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.