jeffthewookiee has asked for the wisdom of the Perl Monks concerning the following question:

I've written a program specifically to keep batches of X processes running concurrently. My company uses this program to automate long-running tasks and keep our servers running as many at a time as possible without overrunning the system. To do this, my perl script periodically checks the status of its child processes (kicked off with a call to open()) using the waitpid() function. This works like a charm in the Linux world but doesn't perform as expected in the Windows world. The code I think is the problem is the following: 
sub check_for_completed_processes
{
   my @completed;
   my @temp;
 #  print "Checking for completed procs...\n";
   while(my $running = pop @running)
   {
      if(waitpid($running -> {process_id} ,&WNOHANG))
      {
         $running -> {end_time} = timestamp();
       #  print "Finished. \n";
         push @completed, $running;
         print "Process completed: " . $running -> {process} . "\n";
         print "Started at: " . $running -> {start_time} . "\n";
         print "End time: " . $running -> {end_time} . "\n";
      }
      else
      {
         push @temp, $running;
      }
   }
   @running = @temp;
   return @completed;                                                 
+                              
}

[download]
This is being run on Windows Server 2003. Is there a way in the Windows world to do a non-blocking waitpid() call or equivalent?

Replies are listed 'Best First'.
Re: waitpid and Windows
by BrowserUk (Patriarch) on May 31, 2007 at 19:50 UTC
    ... but doesn't perform as expected in the Windows world.

    That's a pretty poor description of the problem. What are you expecting and how does what you are seeing differ from that?

    The non-blocking form of waitpid seems to work fine on my system: 

    use POSIX qw[ :sys_wait_h ];;
$pid = open O, '| perl.exe -e"sleep 10; exit(123)"' or die $!;;
print waitpid( $pid, &WNOHANG ) while sleep 1;;
0
0
0
0
0
0
0
4360
-1
-1
-1
Terminating on signal SIGINT(2)

    [download]

    So how is it "not performing as expected" for you?

    Also, showing the open being used woudl be a good idea as that can influence things.

    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
      It seems to hang on the waitpid() call instead of returning immediately and moving on to the next loop step.
[reply]
        It seems to hang on the waitpid()

        It's not hanging - you're just not seeing the output.

        To see the output you'll need to run BrowserUK's code as perl -l script.pl. Alternatively, you could change the third line of the code to: 
        print waitpid( $pid, &WNOHANG ), "\n" while sleep 1;;

        [download]
        Cheers,
        Rob
[reply]
[d/l]
[select]

        Did you try running the snippet I posted above?

        Here it is as a one-liner in case you couldn't see how to run it. (You'll need to enter it as a single line.) 

        C:\test>perl -MPOSIX=:sys_wait_h 
-le"$pid=open O, q[perl -esleep(10)|];print waitpid $pid,&WNOHANG whil
+e sleep 1"
0
0
0
0
0
0
0
0
0
3204
-1
-1
Terminating on signal SIGINT(2)

        [download]

        You'll need ^C to terminate it. What results did you see?

        If you can eliminate your installation and platform as a source of the problem, then you might look more closely at your implementation. Maybe post a bit more code? Including the open as I requested?

        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
Re: waitpid and Windows ($])
by tye (Sage) on Jun 01, 2007 at 00:32 UTC

    Perhaps you are just using too old of a version of Perl, one from before async waitpid was supported on Win32.

    - tye        

[reply]
      I'm using ActiveState perl v.5.8.8
[reply]

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