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Habanero-Java (HJ) is a pedagogic parallel programming model being developed at Rice University. It includes a powerful set of task-parallel programming constructs that can be added as simple extensions to standard Java programs to take advantage of current and future multicore and heterogeneous architectures. Past implementations of HJ required language extensions to Java with special compiler support. In this tutorial, we will focus on the new library implementation of HJ called HJ-lib that can be used with any standard Java 8 implementation. HJ integrates a wide range of parallel programming constructs (e.g., async tasks, futures, data-driven tasks, forall, barriers, phasers, transactions, actors) in a single programming model that enables unique combinations of these constructs (e.g., nested combinations of task and actor parallelism). The orthogonal classes of parallel constructs enables programmers with a basic knowledge of Java to get started quickly with expressing a wide range of parallel patterns. HJ is capable of expressing many different forms of parallel patterns including data parallelism, pipeline parallelism, stream parallelism, loop parallelism, and divide-and-conquer parallelism.
HJ-lib puts a particular emphasis on the usability and safety of parallel constructs. For example, no HJ program using async, finish, isolated, and phaser constructs can create a logical deadlock cycle. Further, the future and data-driven task extensions to the async construct facilitate a functional approach to parallel programming. Finally, any HJ program written with async, finish, and phaser constructs that is data-race free is guaranteed to also be internally and externally deterministic.
HJ-lib is built using Java 8 closures and can run on any Java 8 JVM. Older JVMs can be targeted by relying on external bytecode transformations tools for compatibility. The HJ runtime is responsible for orchestrating the creation, execution, and termination of HJ tasks, and features both work-sharing and work-stealing schedulers. HJ is used at Rice University as an introductory parallel programming language for second-year undergraduate students. A wide variety of benchmarks have been ported to HJ, including a full application that was originally written in Fortran 90.
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