Basically: since usnic is a connectionless transport, we do not get
OS-provided services "for free" that connection-oriented transports
get, namely: "hey, I wasn't able to make a connection to peer X", and
"hey, your connection to peer X has died."
This connectivity-checker runs in a separate progress thread in the
usnic BTL in local rank 0 on each server. Upon first send in any
process, the connectivty-checker agent will send some UDP pings to the
peer to ensure that we can reach it. If we can't, we'll abort the job
with a nice show_help message.
There's a lengthy comment in btl_usnic_connectivity.h explains the
scheme and how it works.
Reviewed by Dave Goodell.
cmr=v1.7.5:ticket=trac:4253
This commit was SVN r30860.
The following Trac tickets were found above:
Ticket 4253 --> https://svn.open-mpi.org/trac/ompi/ticket/4253
7440f21b75