in reply to Fork and wait question

You wait in the child instead of in the parent. You might want to look at something like Parallel::ForkManager to handle this kind of thing for you. Otherwise, the easiest thing to do is wait 16 times outside the loop to collect all the children.

You might also want to keep track of all the child PIDs so you can tell which you've reaped and which are still hanging around. If something is taking too long, it might be helpful to be able to kill it.

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Re^2: Fork and wait question
by pc88mxer (Vicar) on Jun 12, 2008 at 16:24 UTC
    kyle is right - your call to wait is in the child and it should be in the parent. Actually, since it is right after the exec it will never get called under normal circumstances.

    To spawn a new child process, use: 

      die "unable to fork: $!" unless (defined(my $id = fork());
  if ($id == 0) {
    exec($testpath) or die "unable to exec $testpath: $!\n";
  }

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    and after the spawning loop, use: 
    while (wait > -1) {};

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    to wait for all of your children to terminate.
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      ok, I I added what you requested. However it still will continue the program and finish. I can pull up process on my linux and it shows the two instances of the chirp_md5sum program running. 
      $index=0;

my $inputfile="perloutput";
my $endfile=".txt ";
my $smb="> ";
my $outputfile="output";
my $smb2="&";

while ($index<2)
{
   my $testpath="chirp_md5sum ";
   $testpath=$testpath.$inputfile.$index.$endfile.$smb.$outputfile.$in
+dex.$endfile.$smb2;
   chomp $testpath;
   print ("$testpath \n");

   $id=fork();

   if ($id == 0) {
    exec($testpath) or die "unable to exec $testpath: $!\n";

  }

 $index++;
}

while (wait > -1) {};

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