You are thinking corectly. I notice it works on a newer 64 bit machine and fails on older, slower, 32 bit machines with minimum ram for Ubuntu ( 512 Mb).

Also, you are going to find that io operations will block anything if they are hung. So the solution for you, is to put the /dev/dsp read io watch into a separate thread. See Threads-w-Perl/Gtk2 demo for a simplistic example.