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Subject: Re: [OMPI devel] hcoll destruction via MPI attribute
From: Jeff Squyres (jsquyres) (jsquyres_at_[hidden])
Date: 2014-01-10 09:31:39

On Jan 10, 2014, at 9:19 AM, George Bosilca <bosilca_at_[hidden]> wrote:

> However, one should keep in mind that MPI_Comm_free does not have to be a collective function, thus making any type of collective assumption/communications inside the attribute destructor might lead to deadlocks in future versions.

Actually, MPI-3 defines MPI_COMM_FREE as collective (p248:23).

> In other words if the only thing you do in the attribute descriptor is tearing down locally posted requests, then you are safe. If you send data using the communicator then you’re definitively playing dangerously with the safety line.

I still agree with this point, though -- even though COMM_FREE is collective, you could still get into ordering / deadlock issues if you're (effectively) doing communication inside it.

Jeff Squyres
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