gistfile1.rs

spawn(proc(){    
    let (port,chan): (comm::Port<Message>, comm::Chan<Message>) = comm::Chan::new();
    let mut chan = ~chan;
    set_c_callback(c_callback, cast::transmute(&mut *chan));
    loop{
       //...
    }
});

extern "C" fn c_callback (data: *c_void){
    unsafe{
	let channel = data as *mut comm::Chan<Message>;
        (*channel).send(MessageType);
    }
}