  Numerical solutions to the Eikonal equation are computed using variants of
the fast marching method, the fast sweeping method, and the fast iterative
method. In this paper, we provide a unified view of these algorithms that
highlights their similarities and suggests a wider class of Eikonal solvers. We
then use this framework to justify applying concurrent priority scheduling
techniques to Eikonal solvers. We demonstrate that doing so results in good
parallel performance for a problem from seismology. We explain why existing
Eikonal solvers may produce different results despite using the same
differencing scheme and demonstrate techniques to address these discrepancies.
These techniques allow us to obtain deterministic output from our asynchronous
fine-grained parallel Eikonal solver.
