$SIG{CHLD} = sub {while (waitpid(-1, WNOHANG) > 0){} };

##</code><code>##

 $SIG{CHLD} = 'IGNORE' # This often works with a few exceptions. 
                          # set 'IGNORE' is fastest if it does work.
                          # But there is something to be said for working
                          # all the time, albeit slower (see first solution)