NTSTATUS
NtReplyWaitReplyPort(
  IN  HANDLE PortHandle,
  IN OUT PPORT_MESSAGE ReplyMessage
  );

Routine Description:

    A client and server process can send a reply to a previous message and
    block waiting for a reply using the NtReplyWaitReplyPort service:

    This service works the same as NtReplyPort, except that after delivering
    the reply message, it blocks waiting for a reply to a previous message.
    When the reply is received, it will be placed in the location specified
    by the ReplyMessage parameter.

Arguments:

    PortHandle - Specifies the handle of the communication port that the
        original message was received from.

    ReplyMessage - Specifies a pointer to the reply message to be sent.
        The ClientId and MessageId fields determine which thread will
        get the reply.  This buffer also receives any reply that comes
        back from the wait.

Return Value:

    Status code that indicates whether or not the operation was
    successful.