Today's shared-memory parallel programming models are complex and error-prone.While many parallel programs are intended to be deterministic, unanticipated thread interleavings can lead to subtle bugs and nondeterministic semantics. In this paper, we demonstrate that a practical type and effect system can simplify parallel programming by guaranteeing deterministic semantics with modular, compile-time type checking even in a rich, concurrent object-oriented language such as Java. We describe an object-oriented type and effect system that provides several new capabilities over previous systems for expressing deterministic parallel algorithms.We also describe a language called Deterministic Parallel Java (DPJ) that incorporates the new type system features, and we show that a core subset of DPJ is sound. We describe an experimental validation showing thatDPJ can express a wide range of realistic parallel programs; that the new type system features are useful for such programs; and that the parallel programs exhibit good performance gains (coming close to or beating equivalent, nondeterministic multithreaded programs where those are available).

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Not since the advent of the integrated development environment has a development tool had the impact on programmer productivity that refactoring tools have had for objectoriented developers. However, at the present time, such tools do not exist for high-performance languages such as C and Fortran; moreover, refactorings specific to highperformance and parallel computing have not yet been adequately examined. We observe that many common refactorings for object-oriented systems have clear analogs in procedural Fortran. The Fortran language itself and the introduction of object orientation in Fortran 2003 give rise to several additional refactorings. Moreover, we conjecture that many hand optimizations common in supercomputer programming can be automated by a refactoring engine but deferred until build time in order to preserve the maintainability of the original code base. Finally, we introduce Photran, an integrated development environment that will be used to implement these transformations, and discuss the impact of such a tool on legacy code reengineering.

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