Changing the client to leave its socket as blocking during the connect doesn't solve the problem by itself - you also have to introduce a sleep delay once the backlog is hit to avoid simply machine-gunning your way thru retries. This gets somewhat difficult to adjust as you don't want to unnecessarily prolong startup time.
We've solved this before by adding a listening thread that simply reaps accepts and shoves them into the event library for subsequent processing. This would resolve the problem, but meant yet another daemon-level thread. So I centralized the listening thread support and let multiple elements register listeners on it. Thus, each daemon now has a single listening thread that reaps accepts from multiple sources - for now, the orte/pmix server and the oob/usock support are using it. I'll add in the oob/tcp component later.
This still didn't fully resolve the SMP problem, especially on coprocessor cards (e.g., KNC). Removing the shared memory dstore support helped further improve the behavior - it looks like there is some kind of memory paging issue there that needs further understanding. Given that the shared memory support was about to be lost when I bring over the PMIx integration (until it is restored in that library), it seemed like a reasonable thing to just remove it at this point.
So we need all the routing code for dealing with cross-job communications, lifelines, etc. The HNP will be directly connected to all daemons as they must callback at startup, and so we need to track those children correctly so we know when it is okay to terminate.
We still have to support direct launch, though, as this is the only component we can use in that scenario. So if the app doesn't have daemon URI info, then it must fall back to directly connecting to everything.
VERY tentatively schedule this for 1.7.5 - only to be applied if we see no troubles AND the branch is ready in advance.
cmr=v1.7.5:reviewer=rhc:subject=Add unix socket component to OOB
This commit was SVN r30742.
