Subject: order preservation

From: [email-masked] (Ambuj Singh)
Date: Fri, 5 Feb 93 14:42:13 PST

Hello:

The issue of order preservation of messages when there
are multiple threads at the sender was not clarified
at the January meeting.  What do people have to say about
this?  It seems that there is no need to require message
orderings across different threads.  In other words,
the order that the messages are received should be
consistent with the ``program order'' which is defined
by the order in which statements get executed.  Thus
messages in different threads may not be related and
there should not be a need to preserve their order.

On a different note, there was some question regarding
the need for a synchronous send operation.  One reason
that they may be useful is that they might be the only
means to ensure true portability.  As illustrated by the
following program that we discussed at the January
meeting, asynchronous send operations are not portable
across  CM-5 and Intel.

                    Process 1      Process 2
                    ---------      ---------
                    send to 2      send to 1
                    recv           recv

In other words, the standard could inquire that programs
employing synchronous send/receive operations be portable
across machines.  It would be difficult to meet the
same requirement for the asynchronous operations.

--Ambuj Singh
Dept. of CS, UCSB