/// Send a signal to a thread.
///
/// # Examples
///
/// ```
/// let pid = unsafe { nc::fork() };
/// assert!(pid.is_ok());
/// let pid = pid.unwrap();
/// assert!(pid >= 0);
///
/// if pid == 0 {
/// // child process.
/// let mask = nc::sigset_t::default();
/// let ret = unsafe { nc::rt_sigsuspend(&mask) };
/// assert!(ret.is_ok());
/// } else {
/// // parent process.
/// let t = nc::timespec_t {
/// tv_sec: 1,
/// tv_nsec: 0,
/// };
/// let ret = unsafe { nc::nanosleep(&t, None) };
/// assert!(ret.is_ok());
///
/// let ret = unsafe { nc::tgkill(pid, pid, nc::SIGTERM) };
/// assert!(ret.is_ok());
/// }
/// ```
pub unsafe fn tgkill(tgid: i32, tid: i32, sig: i32) -> Result<(), Errno> {
let tgid = tgid as usize;
let tid = tid as usize;
let sig = sig as usize;
syscall3(SYS_TGKILL, tgid, tid, sig).map(drop)
}