sub trap_signals {
  local $SIG{CHLD} = \&handler;
  :
}

##</code><code>##

sub init {
   $SIG{CHLD} = ...;
   ... init code ...
}

{
   init()
   ... main code ...
}

##</code><code>##

sub main {
   ... main code ...
}

{
   local $SIG{CHLD} = ...;
   ... init code ...
   main();
}