random code snippet (cooperative threading)

[Matthijs van Duin]

I recently fiddled around a bit with how one might implement cooperative 
threading in perl 6 using call-with-current-continuation (callcc), so I 
thought I'd share it with you

(since continuations are often poorly understood, more examples is always 
better :-)

This is assuming callcc exists and that the continuation is topic inside it; 
if that's not a built-in then callcc can no doubt be defined using whatever 
is available to make continuations.

Enjoy!

my @queue;

sub thread_exit () {
        shift(@queue)(undef);
        exit;
}
sub thread_new (&code) {
        push @queue, callcc {
                unshift @queue, $_;
                code;
                thread_exit;
        }
}
sub thread_yield () {
        if @queue {
                my $prev = callcc shift @queue;
                push @queue, $prev  if $prev;
        }
}


thread_new {
        for 1..10 -> $i {
                print "foo: $i\n";
                thread_yield;
        }
}
thread_new {
        for 1..10 -> $i {
                print "bar: $i\n";
                thread_yield;
        }
}
thread_new {
        for 1..10 -> $i {
                print "baz: $i\n";
                thread_yield;
        }
}
thread_exit;

--
Matthijs van Duin  --  May the Forth be with you!