Asserts that error.Canceled was returned from a prior cancelation point, and "re-arms" the
cancelation request, so that error.Canceled will be returned again from the next cancelation
point.
For a description of cancelation and cancelation points, see Future.cancel.
pub fn recancel(io: Io) void
pub fn recancel(io: Io) void {
io.vtable.recancel(io.userdata);
}