[ofiwg] help analyzing ring buffer implementation

[Hefty, Sean]

There is an open issue that is reporting a possible threading problem with the ring buffer implementation in libfabric:

https://github.com/ofiwg/libfabric/issues/3303

In analyzing the code, I suspect that this is a false warning, though I can see how a thread analyzer would report a problem with the code.  At the same time, additional locking does quiet the warning.  If you're a multi-threaded coding expert, please take a look at the open issue and/or ring buffer implementation and help determine if there is a real issue.

For reference, the ring buffer is written to allow simultaneous access reading and writing to the ring buffer.  Serialization of readers and writers is left up to the caller.

https://github.com/ofiwg/libfabric/blob/master/include/fi_rbuf.h#L105

- Sean