[OMPI devel] v1.2 branch mpi_preconnect_all

[Don Kerr]

All,

I have noticed an issue in the 1.2 branch when mpi_preconnect_all=1. The 
one way communication pattern (ranks either send or receive from each 
other) may not fully establish connection with peers. Example, if I have 
a 3 process mpi job and rank 0 does not do any mpi communication after 
MPI_Init() the other ranks attempts to connect will not be progressed (I 
have seen this with tcp and udapl).  
The preconnect pattern has changed slightly in the trunk but essentially 
it is still a one way communication, either send or receive with each 
rank. So although the issue I see in the 1.2 branch does not appear in 
the trunk I wonder if this will show up again.

An alternative to the preconnect pattern that comes to mind would be to 
perform a send and receive between all ranks to ensure that connections 
have been fully established.

Does anyone have thoughts or comments on this, or reasons not to have 
all ranks send and receive from all?

-DON