Function wait

pub fn wait<P>(pid: P) -> Result<WaitStatus>
where
    P: Into<Option<pid_t>>,

Wait for one of the children of the calling process to terminate and return a WaitStatus. Note that is function will block until a child termination status becomes available.

If pid is greater than 0, wait for the child whose process ID equals pid. In case pid is None, wait for any child of the calling process