VMS Help TCPIP Services, Programming Interfaces, Sockets API, select(), Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    This function determines the I/O status of the sockets specified
    in the various mask arguments. It returns when a socket is ready
    to be read or written, when the timeout period expires, or when
    exceptions occur. If timeout is a non-null pointer, it specifies
    a maximum interval to wait for the selection to complete.
    If the timeout argument is null, the select() function blocks
    indefinitely until a selected event occurs. To effect a poll,
    the value for timeout should be non-null, and should point to a
    zero-value structure.
    If a process is blocked on a select() function while waiting for
    input for a socket and the sending process closes the socket,
    then the select() function notes this as an event and unblocks
    the process. The descriptors are always modified on return if the
    select() function returns because of the timeout.
                                   NOTE
       When the socket option SO_OOBINLINE is set on the device
       socket, the select() function on both read and exception
       events returns the socket mask that is set on both the read
       and the exception mask. Otherwise, only the exception mask
       is set.
    Related Functions
    See also accept(), connect(),  read(), recv(), recvfrom(),
    recvmsg(), send(),  sendmsg(), sendto(), and write().