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while (1) {
   sleep 1;
   ...
}

while (1) {
   sleep 1;
   my $thread = threads->new(\&work_sub);
}

#!/usr/bin/perl -w

...
   my $thread = threads->new( sub { print "foo"; sleep 1; print "\n" }
+);
   $thread->detach;
}

join() does three things: it waits for a thread to exit, cleans up 
after it, and returns any data the thread may have produced.
...
In this case, you use the detach() method.  Once a thread is 
detached, it'll run until it's finished, then Perl will
clean up after it automatically.