Concurrent depth-first search algorithms based on Tarjan's Algorithm

We present concurrent algorithms, based on depth-first search, for three problems relevant to model checking: given a state graph, to find its strongly connected components, which states are in loops, and which states are in "lassos". Each algorithm is a variant of Tarjan's Algorithm. Our algorithms typically exhibit a three- or four-fold speed-up over the corresponding sequential algorithms on an eight-core machine.