Here is a version that works for me. Don't forget to print your header first, to get things going.

#!/usr/bin/perl
use warnings;
use strict;
use threads;
use threads::shared;

print "Content-type: text/html\n\n";
print "Starting work<br>\n";

$|++;

# set a shared value of TRUE for running the progress bar
my $keepRunningProgressBar : shared = 1;


# Set the progress bar running indefinitely
my $progressBar = threads->create( \&dot_thread )->detach;

# Now do stuff in the work thread
my $threadForSpidering = threads->new( \&workthread );

#The work thread finished
#$threadForSpidering->join; #you have 3 threads, not just one
#main, dot_thread, and workthread
#And tells the progress bar to stop running
$keepRunningProgressBar = 0;

#<>;  #without waiting here you get the thread exited error
foreach my $thread ( threads->list ) {
   $thread->join;
}

print "done<br>.\n";
exit;
##########################################################

sub dot_thread {
   $|++;
   while ( $keepRunningProgressBar == 1 ) {
      print ".\n";
      sleep( 1 );
   }
}

sub workthread {
   for ( 1 .. 10 ) {
      print "\tworking\n";
      sleep 1;
   }
}
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