Jeff paraphrased an unnamed source as suggesting that: "any MPI program that relies on a barrier for correctness is an incorrect MPI application." . That is probably too strong.
How about this assertion?
If there are no wildcard receives - every MPI_Barrier call is semantically irrelevant.
It is the exception that tests the rule.
If someone can provide an example of an MPI_Barrier that is required by an application based on MPI communication and that does not use wildcard receive I am interested in seeing it. I do not know of a counter example but also do not have proof of the assertion I place before the group.
No fair using examples with non-MPI interactions among tasks or with job steering by asynchronous triggers from outside the job. I can construct them myself.
MPI_WIN_FENCE is semantically required in some situations and examples that show a semantic need for MPI_WIN_FENCE do not count against the assertion.
I have appreciated the descriptions from Gus, Asjley and others of some non-symantic justifications for an MPI_Barrier.
Dick Treumann - MPI Team
IBM Systems & Technology Group
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