J3/07-127
To: J3
Date: 24 January 2007
From: Bill Long and John Reid
Subject: UTI 86: image-team value
References: J3/07-007

Discussion

UTI 86 (page 200) asks if it would be better to have the SYNC TEAM statement
verify that the executing image is part of the image-team, as opposed
to making the program non-conforming if that is not the case. We
believe the answer is no.  The point of teams is high performance.
Adding this required check into the execution of a SYNC TEAM statement
is counter to that goal. Furthermore, the check burden gets increasing
large as the number of images grows, potentially hurting scaling as
well.

A programmer can extract the list of images from an image-team
variable with the TEAM_IMAGES intrinsic function and perform a check
if desired. In addition, an implementation is allowed to have a debug
mode that would link in slower versions of the sync statements that
could do checking of this sort.  But requiring this check all the time
is undesirable.

If a check to validate the value of an image-team variable is seen as
a requirement, it should be done in the FORM_TEAM intrinsic
subroutine, where the check's affect on performance would be less
significant.  Assuming a team is cleanly formed, it should not later
become defective, so checks in later usage would be a unnecessary.


Edits to J3/07-007

(none)