Using File::Cache seemed to produce strange behaviour which I attribute to file locking or sharing issues and race conditions between the two processes. I've updated the code to use CGI::Session instead which not only seems to have fixed the problem, but also removes the need to generate an ID explicitely.

Not however the use of flush () in the main loop of the long process to ensure the data is flushed through to the monitoring process.

#!Perl -w
use strict;
use CGI::Pretty qw(:standard :cgi-lib);
use CGI::Carp qw(fatalsToBrowser); # Remove for production code
use CGI::Session;

$CGI::DISABLE_UPLOADS = 1;         # Disable uploads
$CGI::POST_MAX        = 10240; # Maximum number of bytes per post

$| = 1; # Unbuffered output

if (param('Spawn')) {
    # setup monitoring page then spawn the monitored process
    my $cache = CGI::Session->new ();
    my $session = $cache->id();
   
    $cache->param ('status', "wait ..."); # no data yet
    Delete_all();
   
    # parent redirects browser to monitor session
    param('session', $session);
    print redirect (self_url());
    close STDOUT;

    # Rest of this block alters in *nix context to spawn monitored pro
+cess
    use Win32::Process;
   
    my $job;
   
    Win32::Process::Create (
        $job,
        'c:/Perl/bin/perl.exe', "perl.exe spawned.pl \"$session\"",
        0,
        NORMAL_PRIORITY_CLASS | DETACHED_PROCESS,
        '.'
        );

    exit 0; # all done
 
} elsif (my $session = param('session')) {
    # display monitored data
    my $cache = CGI::Session->new ($session);
    my $data = $cache->param ('status');
   
    if (! $data) { # something is wrong
        showError ("Cache data not available");
        exit 0;
    }
   
    my $headStr = $data eq 'Completed' ? '' : "<meta http-equiv=refres
+h content=5>";
    print header();
    print start_html (-title => "Spawn Results", -head => [$headStr]);
    print h1("Spawn Results");
    print pre(escapeHTML($data));
    print end_html;
 
} else {
    # display spawn form
    print header(), start_html("Spawn"), h1("Spawn");
    print start_form();
    print submit('Spawn', 'spawn');
   
    my %params = Vars ();
    for my $param (keys %params) {
        print br ("$param -> $params{$param}");
    }
   
    print end_form(), end_html();
}

exit 0;


sub showError {
    print header(), start_html("SpawnError"), h1("Spawn Error");
    print p (shift);
   
    my %params = Vars ();
    for my $param (keys %params) {
        print br ("$param -> $params{$param}");
    }
   
    print end_html();
}

[download]

The monitored (long running) process:

#!Perl -w
use strict;
use CGI::Session;

my $session = shift;
my $cache = CGI::Session->load ($session);

$cache->param('status', "configuring ..."); # no data yet

my $end = time () + 20;
my $count = 0;

while (time () < $end) {
    $cache->param ('status', "Count: $count\n");
    $cache->flush ();
    ++$count;
    sleep (1);
}

$cache->param ('status', "Completed");
$cache->flush ();
exit 0; # all done

[download]
DWIM is Perl's answer to Gödel

In reply to Re^2: Managing a long running server side process using CGI by GrandFather
in thread Managing a long running server side process using CGI by GrandFather

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.