Disclosed is a method, system, and computer program product for implementing a costed-search approach that supports concurrent operation on a multi-CPU system that enables out-of-order search evaluation that does not affect the final outcome of the algorithm. The algorithm is guaranteed to produce identical results when run as a single-threaded application on a single-CPU system. This allows a single regression test suite to be used to test single-threaded and multi-threaded versions of the product.