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

Hello Monks,
Want to know about CGI. I have a script burn.pl, which creates a web page using CGI.pm. Simple enough. Now, inside this, it should fork another perl script, called sleep.pl, which should sleep until I send it a SIGALRM. This all works, but the web page continues to have the hour glass (like the page is waiting for input from the CGI) until I send my sleeping process the SIGALRM. How would I get the web page to do the complete job (i.e. not wait with the hourglass) while still running the sleep.pl in the background?

#!/usr/bin/perl -w #Create initial feedback page
use CGI ':standard';

my $query=new CGI;

print $query->header("text/html");
print $query->start_html(-title => "This is my first web page generate
+d via CGI");
print $query->h1('This is the header document');
print <<EOF;
This is the body of the document<br/>
What goes in here is really anything you wish to put in here<br/>
EOF
if ( my $pid = fork() ) {
   system ("./sleepme.pl");
   exit; # This current process
} else {
   print $query->end_html;
}

[download]

My sleep.pl is simple: 
#!/usr/bin/perl -w
sleep;
exit;

[download]
I know little about CGI, so this is all a bit new to me.
Thanks
H

20040504 Edit by broquaint: Changed title from 'CGI question - getting rid of the hour glass'

Replies are listed 'Best First'.
Re: Closing parent CGI after fork()
by tinita (Parson) on May 04, 2004 at 11:57 UTC
    try: close STDOUT; before the system call.

    update: just trying it out and i'm not getting it to work, but i remember it used to work by closing STDOUT... update2: works. you might also want to do exec() instead of system().

[reply]
[d/l]
[select]
      You probably want to close STDIN and STDERR too
[reply]

        You probably want to close STDIN and STDERR too

        You probably don't want to do any of this stuff, but you'll find you have to... :(

        Even though the valuable information found by following links to merlyn's nodes/articles elsewhere in this thread only talk about closing STDOUT, I found I had to close STDIN and STDERR, as well. This is for Apache 2. I had to jump through some hoops to redirect the child's STDERR to a file and later send anything found there to the apache error_log, rather than lose any STDERR output produced by the child... a bit ugly, but it works.

        Also, I found I had to reopen all 3 filehandles (to/from /dev/null for STDOUT and STDIN, to a file for STDERR) as well, since my child is opening other files, and if you just close STD(IN|OUT|ERR), the next time you open a file it will get file descriptor 0, 1, or 2, which is essentially reopening STD(IN|OUT|ERR), and I found this causes apache to hang again! Ugh. forker beware!

        HTH

        --
        edan

[reply]
Re: Closing parent CGI after fork()
by b10m (Vicar) on May 04, 2004 at 13:03 UTC
[reply]
Re: Closing parent CGI after fork()
by pelagic (Priest) on May 04, 2004 at 13:02 UTC
[reply]

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