Experts will tell you to use Thread::Queue. I have not much experience with queues. However this is what you can achieve with shared variables: 
use threads;
use threads::shared;

my ($global):shared;

my $handler=threads->create(\&handler)->detach;

do
    {
    
    print "Enter a value for shared global variable ( x = exit ): ";ch
+omp($global=<>);
    
    sleep(3);
    
    } while($global ne 'x');

sub handler
{

my $global_old=$global;

while(1)
    {

    if($global ne $global_old)
        {
        
        print "User changed the global variable to '$global'.\n";
        $global_old=$global;
        
        }

    sleep(1);

    }

}

[download]

In reply to Re^9: Execute a sub in the background by chessgui
in thread Execute a sub in the background by egzoti4en

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.