Exec command running in background after a fork

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

Hi All, How can i make the code below to run in background (windows xp) until the command ends?

The command is similar to "perl main.pl a b c d e". If i put this command at #child place, the script (main.pl) runs until it terminates but the html page (#parent place) is only loaded after the script ends. I want to display the html page as soon as the script starts.

If i change the code between #child and #parent fields, the html is displayed instantly but the script (main.pl) is killed and is not executed to the end.

use warnings;
use strict;

$| = 1; # need either this or to explicitly flush stdout, etc.
# before forking
print "Content-type: text/plain\n\n";
print "Going to start the fork now\n";
if ( !defined(my $pid = fork())) {
print STDERR "fork error\n";
exit(1);
} elsif ($pid == 0) {
# child
close(STDOUT);close(STDIN);close(STDERR);
exec('perl main.pl a b c d e'); # lengthy processing
} else {
# parent
print "forked child \$pid= $pid\n";
exit 0;
}
__END__
[download]

This script main.pl takes at least 5 minutes running. This is the reason that i can't wait the script terminates.

My main.pl script will receive a huge file from a form and parse the file into a database. After this process, some configurations from the database that the user has just populated will appear on screen to the user..

Thanks!

Comment on Exec command running in background after a fork Download Code

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Re: Exec command running in background after a fork by 1Nf3 (Pilgrim) on May 22, 2009 at 14:19 UTC
A while ago, I wrote some chessgame-analysis-related program. The analysis process took a looong while, so I had to find a way to execute the external analysis utility in the background. I'm not sure whether the same solution will be used here, but here is the command execution part: `system 1, 'perl main.pl a b c d e';` [download] The Documentation advises against the use of exec (see http://perldoc.perl.org/functions/exec.html), so I'd use system instead. Hope that halps. Regards, Luke	[reply] [d/l]
Re: Exec command running in background after a fork by Bloodnok (Vicar) on May 22, 2009 at 14:30 UTC
Hmmm , The problem would appear to be that you spawned a child, told it to go away and do something and then neglected to hang around waiting for your child to finish e.g. `. . } else { # parent print "forked child \$pid= $pid\n"; wait(); # Added exit 0; } . .` [download] A user level that continues to overstate my experience :-))	[reply] [d/l]