Function twz_rt_fd_waitpoint 

pub unsafe extern "C-unwind" fn twz_rt_fd_waitpoint(
    fd: descriptor,
    ek: wait_kind,
    point: *mut *mut u64,
    val: *mut u64,
    ready: *mut bool,
) -> twz_error

Get a word and value to wait on for determining if reads or writes are available.