<EXAMPLE>
#!/usr/bin/perl
sub 1 {
   while(1) {
       print "in sub 1 \r\n";
   }
sub 2 {
   while(1) {
       print "in sub 2 \r \n";
   }
}
&sub1();
&sub2();

output :
in sub 1
in sub 2
(endless :p)