Perl Background Process - Finshed Yet?

Shell Programming and Scripting
1

I have a perl process I want to run in background in a cgi, but do not
want to continue until process finished code looks like this.

sub calc(){
do calculations
return value
}

In another Perl program I call above function such as

&calc();

I want to continue after process finishes.

Any Ideas on how to do this.

Thanks

2

for finer control over processes, check out Proc::Simple
Please note that sub calc () is a subroutine, and not a process.

If you are calling this subroutine from some other place, then the regular behavior is what you have described:

#!/usr/bin/perl
# sub_trial.pl
use strict;
sub calc ()
{
    print "in calc() now ... \n";
    sleep 10;  # wait for 10 seconds
      # or do something here
}
print "we're in main script ... \n";
calc ();
print "and continued ... \n";
3

actually it is a little more complicated then my simple example, but
basically by the time the background process &calc finishes my page
has loaded, so I have to keep refreshing the page until &calc() finishes.

The reason for this is, once &calc enters values
into database, then final page can be reloaded only once instead of
multiple times.

Obviously, I will have to run it in a

unless(my $pid = fork()){&calc();}

or
something like that. When &calc() finishes reload page once.

4

Does this help (I mean the non-blocking wait example shown)?

waitpid - perldoc.perl.org

Of course, as a CGI script is executed once for each HTTP request, you must keep the process ID you are monitoring somewhere, say on the filesystem or session.

5

Its funny none of the perl books I have had anything on waitpid. I had to go to the Stevens book, but waitpid is the solution I came up with too.
.

defined(my $pid = fork()) or die "Cannot fork: $!";
if($pid){
    ## waitpid($pid, 0);
    ## or if you want the pid
    do{
        $kid = waitpid(-1, WNOHANG);
        $count_pid = $kid;
    }until $kid > 0;

    $out .= qq|<hidden type="count_pid" value="$count_pid">|;
    ## javascript redirect here
}else{
    &calc();
    CORE::exit(0);
}

It works good, but still looking for a way to improve. I may have to use AJAX or something to get rid of reloads.