Article 166953 of comp.os.vms:
At 00:03 03-04-1997 GMT, mathog@seqaxp.bio.caltech.edu wrote:
>Mailboxes are great for communicating with one process at a time,
>or for collecting input from a bunch of processes if they can stamp their
>identification inside the records they write, or if you don't care which 
>process wrote which record, but mailboxes can be a pain when you
>have to deal with a bunch of (sub)processes all writing records to a single
>process AND you care who writes what.  In that case, you generally need one
>mailbox per line of communication, and often, many, many mailboxes.
>
>Wouldn't it be nice if there was a special "fan in" mailbox?  Every time it
>was read the result would be both a record AND the PID of the
>process that wrote it.

Check the second longword of the IOSB. It contains the PID of the sender!
=======================================================
Nigel White  (nigel@synergex.com)
Systems Programmer, Synergex (Formerly DISC)
2330 Gold Meadow Way; Gold River, CA 95670
Phone: 916/8530366; Fax: 916/635-6549; WWW: http://www.synergex.com