Signal on process end

["Ratcliffe, Jeffrey (Peters)" <Jeffrey Ratcliffe External eads com>]

Sorry this is slightly OT, but: having started a process with:

my ($write, $read);
my $error = IO::Handle -> new;
my $pid = open3($write, $read, $error, $cmd);

How best do I see when the process has finished?

It would be nice if there were some watch like

Glib::IO -> add_watch

or event I could set up. But I can't find anything of the like.

Thanks

Jeff