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From: adelman@LBL-CSA2.ARPA (Kenneth Adelman)
Newsgroups: comp.os.vms
Subject: Re: Dynamic "SYS$ANNOUNCE" (or Sys$Welcome) display
Message-ID: <870807042134.03k@Lbl-Csa2.Arpa>
Date: Fri, 7-Aug-87 07:21:34 EDT
Article-I.D.: Lbl-Csa2.870807042134.03k
Posted: Fri Aug  7 07:21:34 1987
Date-Received: Sun, 9-Aug-87 13:06:49 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: Adelman@Lbl-Csa2.Arpa (Kenneth Adelman)
Distribution: world
Organization: The ARPA Internet
Lines: 20


	I've been using the trick of redirectly SYS$ANNOUNCE to
a mailbox with an attention AST for some time.	Some comments:

    1) Have your program set up an exit handler to restore the
logical SYS$ANNOUNCE to something NOT pointing at a mailbox.
Otherwise if the program dies no one can log in because LOGINOUT
blocks reading the mailbox.

    2) Be aware that it is best to write everything to the mailbox in
one $QIO and include your own carriage-control. If there are two
simultaneous readers the output can become somewhat garbled.  Even
using one $QIO to write the mailbox, the IO$_WRITEOF is not atomic
with the IO$_WRITEVBLK and it possible that one user gets the banner
displayed twice and the other gets none at all. (DEC; are you
listening? How about an IO$M_WRITEOF modifier for IO$_WRITEVBLK to
make this operation atmoic?).

					Kenneth Adelman
					LBL