In the original code, the position key stored in the TT is used to probe&store TT entries after message passing. Since we only store part of the bits in the TT, this leads to incorrect rehashing. This is fixed in this patch storing also the full key in the send buffers, and using that for hashing after message arrival.
Short testing with 4 ranks (old vs new) shows this is effective:
Score of mpiold vs mpinew: 84 - 275 - 265 [0.347] 624
Elo difference: -109.87 +/- 20.88
This reverts my earlier change that only the root node gets to output best move after fixing problem with MPI_Allreduce by our custom operator(BestMoveOp). This function is not commutable and we must ensure that its output is consistent among all nodes.
Previous behavior was to wait on all nodes to finish their search on their own TM and aggregate to root node via a blocking MPI_Allreduce call. This seems to be problematic.
In this commit a proper non-blocking signalling barrier was implemented to use TM from root node to control the cluster search, and disable TM on all non-root nodes.
Also includes some cosmetic fix to the nodes/NPS display.
Based on Peter Österlund's "Lazy Cluster" algorithm,
but with some simplifications.
To compile, point COMPCXX to the MPI C++ compiler wrapper (mpicxx).
