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Subject: [OMPI devel] Inherent limit on #communicators?
From: Ralph Castain (rhc_at_[hidden])
Date: 2009-04-30 14:12:27


Hi folks

We seem to have hit a problem here - it looks like we are seeing a built-in
limit on the number of communicators one can create in a program. The
program basically does a loop, calling MPI_Comm_split each time through the
loop to create a sub-communicator, does a reduce operation on the members of
the sub-communicator, and then calls MPI_Comm_free to release it (this is a
minimized reproducer for the real code). After 64k times through the loop,
the program fails.

This looks remarkably like a 16-bit index that hits a max value and then
blocks.

I have looked at the communicator code, but I don't immediately see such a
field. Is anyone aware of some other place where we would have a limit that
would cause this problem?

Thanks
Ralph