#in main Tk thread
my $fileno = $shash{'fileno'}; #from a shared variable set in thread
print "fileno_m $fileno\n";
open (FH, "<&=$fileno") or warn "$!\n";
           
# filevent works but may not work on win32
   $mw->fileevent(\*FH, 'readable', [\&fill_text_widget,$text]);

#in thread code block
my $pid = open(FH, "top -b |" ) or warn "$!\n";
my $fileno = fileno(FH);
$shash{'fileno'} = $fileno;