This problem can be demonstrated much more simply with this code:

#!/usr/bin/perl -wT

use strict;
use CGI ':standard';

die "Could not fork()\n" unless defined (my $kidpid = fork);
if ($kidpid) {
    print header;
    print "done\n";
    print STDERR "Parent exited\n";
    exit;

}
else
{
    sleep 20;
    print STDERR "Child exited \n";
}

[download]

If you run this CGI at a command prompt, it does what you would expect - the parent exits and you get the command prompt again. 20s later, the child exits and you see the output broadcast in the terminal.

Now run it as a CGI, and although you see "done" printed straight away in the browser, the page still appears to be loading until the 20s is up (the server appears to still be holding the connection open). A clue I found at http://coding.derkeiler.com/Archive/Perl/perl.beginners/2003-11/1136.html implies this could be to do with Apache. I found this issue running with mod_cgid in Apache 2.2.9 on Linux kernel 2.6.27.

My application is AJAX and is experiencing this problem; AJAX cannot solve it directly. My AJAX call cannot determine if the task started successfully, because it does not get the result until it ends. I am going to see if I can work around it by making the call and ignoring the response; hopefully the FF JS engine is multithreaded enough to let me do that.

I would love to hear from anyone who has managed to make Apache let perl fork properly in this scenario. Having said all that, if you read http://www.xav.com/perl/lib/Pod/perlfork.html, it says "the parent and every pseudo-child created by it that is also a pseudo-parent will only exit after their pseudo-children have exited.", so I'm not sure the command prompt example should work as it does.

In reply to Re: PERL CGI - waiting page is hanging by realflash
in thread PERL CGI - waiting page is hanging by chanklaus

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.