Spawning parallel processes

[mwhamilton]

I am essentially trying to create a job queing system. We use a simulator to simulate all of our new hardware designs, and the vhdl simulator is quite slow. The simulator is called with a perl script. I have created a script that checks for machine availability, and also inputs the different test names that should be simulated. I am having one problem when using fork() to spawn processes. Each time I fork, I need to rsh into a different machine on the network. I am not sure when to use system or exec. The simulation takes a long time, so I need multiple simulations running on different machines at the same time. Also, I need to send all of the output back to the original xterm window. Please help! Thanks so much!

# START A NEW CHILD
if ( ( $pid = fork()) == 0 )
{
# CHILD
#Here is where I need to rsh into a new machine
#here is where I need to change directories on the remote machine
#Here is where I need to run the simulation on the remote machine
exit(1);
}
else
{
# PARENT
$children{$pid} = $command_to_execute; #hash links command line to the pid
$count++; #increment number of processes running
}
}

 

[goBoating]

I think using 'open' with '-|' will do what you are looking
for. The open(HANDLE,"-|&quot syntax forks a new child
process that is identical to the parent except that in the
parent $pid is set by that 'open' statement.
- Immediately after the 'open' statement, you have two
process, a parent and a child.
- The parent has $pid set and the child does not. Control your
flow base on $pid. If $pid is set, do parent stufff. If
$pid is null, do child stuff.
- The child picks up executing where the the fork occurs. It
does not start over at the beginning of the code.
- STDOUT from the child goes back to the handle in the parent.
- Make sure you turn on autoflush or you may loose output from
you child processes. They can exit and leave stuff in their
buffers if autoflush is not on.

# Set autoflush on to make sure the children 
# get all their output back to the parent.
$| = 1; 
# In the parent, fire off a child for each rsh
foreach $req (@list_of_requests) {
  last if (!($pid = open($req,"-|"))); 
  # the 'last if' bails out if child process
}
if ($pid)  { 
  # $pid is populated - this must be the parent
  # - listen to each handle previously forked
  # - This is not fully parallel.  Note that in
  #   this example the listening is done in serial
  # 
  foreach $i (@list_of_requests) {
    while (<$i>) { print &quot;$i&quot;; }
  }
}
if (!($pid)) {
  # No pid set, therefore this is a child
  # Do child stuff, print output to parent via STDOUT
  # and exit when finished.
  print &quot;Something back to the parent process
         via STDOUT.\n&quot;;
  exit;   # the child does its work and bails out.
  }
$| = 0; # set AutoFlush back to its default.

See 'Programming Perl' published by OReilly by Wall, Christiansen,
and Schwartz for lots more detail on playing with this stuff.
This example leaves a lot of detail out in favor or brevity, but
hopefully it illustrates an approach. 'hope this helps

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