> Actually I think it is really not so good idea manage reference counter
> across OOB communication.

But this is exactly what the current API *requires* that users of XRC do!!!  
And I agree, it's not a good idea. :)

> IMHO, I don't see a good reason to redefine existing API.
> I afraid, that such API change will encourage MPI developers to abandon XRC
> support.

I'm suggesting that most apps don't need to do anything special.  No OOB 
connections, no special message exchanges carrying XRC numbers, no reference 
counting, no new verbs for xrc recv qps that do the same thing as the existing 
verbs.  Using XRC becomes easier!  The lifetime of the XRC receive QP is simply 
tied to the lifetime of the XRC domain, unless the creating process wants to 
destroy it sooner.

The only reason reference counting was added at all was to support a 
questionable usage model of sharing an xrc domain across jobs.  I'm suggesting 
that *only those apps* that want that usage model can implement it over the 
provided APIs.  They can continue to use OOB connections, pass XRC numbers, 
replace ibv_reg_recv_xrv() with atomic_inc(), and let the persistent server 
destroy the xrc recv qp when those processes are done.  For everyone else (and 
it sounds like this is really everyone at this point), there's simply no need 
for any of that.

- Sean
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