Parallelizing Union-Find in Constraint Handling Rules Using Confluence Analysis

Constraint Handling Rules is a logical concurrent committedchoice rule-based language. Recently it was shown that the classical union-find algorithm can be implemented in CHR with optimal time complexity. Here we investigate if a parallel implementation of this algorithm is also possible in CHR. The problem is hard for several reasons: Up to now, no parallel computation model for CHR was defined. Tarjan’s optimal union-find is known to be hard to parallelize. The parallel code should be as close as possible to the sequential one. It turns out that confluence analysis of the sequential implementation gives almost all the information needed to parallelize the union-find algorithm under a rather general parallel computation model for CHR.