tty_yield?

#1
What sort of message will cause tty_yield() to return?
Code:
void WINAPI tty_yield( int nWait );
/*
   Retrieve messages & give some time to other apps.
   If nWait != 0, wait for a message to arrive before returning
*/
I'd like to implement a "BPAUSE" (or something like that, for batch files) that will do nothing other than pause until a key is pressed. Any suggestions?