AH 4 Dec 2005:
Tcl_DoOneEvent is a public C function exported by the Tcl library.
Tcl_DoOneEvent processes the first event in the event queue. If the queue is empty, it waits for one to occur, then processes it (but see the documentation for exceptions to this rule).
Also see Interaction of the Tcl I/O system with the Tcl Notifier [L1 ] for an in-depth look at Tcl's event loop in action.
Tcl_DoOneEvent is useful if you need to enter Tcl's event loop in C.