I think all you need to do is put a statement-ending semi-colon (;) after these two lines:

my $t1 = async { qx(perl process1); }
my $t2 = async { qx(perl process2); }
[download]

...so they look like this:

my $t1 = async { qx(perl process1); };
my $t2 = async { qx(perl process2); };
[download]

That's what it shows in the threads documentation, and works for me on one of my machines that has a threads capable perl.

-stevieb