Introduction

In this report, we introduce HPJava language, a programming language extended from Java for parallel programming on message passing systems, such as workstation clusters.

Though its name comes directly from HPF[1], HPJava does not inherit HPF completely. The language introduces a high level SPMD programming style, HPspmd, which can be summarized as following,

• Structured SPMD programming The programming language presented here depends on a well organized process group as control threads. As in a SPMD program, only the data owners are allowed to share the current control thread when the data items are accessed. The language offerers special constructs for programs to achieve this conveniently.
• Global name space Besides local variables, the language provides variables associated with data descriptor, offering a global name space, especially, global addressed array with different distribute patterns. This helps to relieve programmers of error-prone activities like local-to-global, global-to-local translations in most data parallel applications.
• Collective communication Accessing data on different processors is through a powerful collective communication library provided with the language. With this library, data parallel applications may have dead-lock free communication. As in SPMD style, the language itself does not provide data movement semantics implicitly. This encourages the programmer to write algorithms that exploit locality and simplifies the task of compiler writers.
• Hybrid of data and task parallel programming The language provides constructs facilitating both data parallel and task parallel programming. Through language constructs, different processors can not only work simultaneously on global addressed data, but also execute independently complex procedures on their own local data. The conversion between these two phases is a seamless one.
• Flexible for future extension The language itself only provides basic concepts to organize a group of process grid. Different communication patterns are implemented as library functions. This gives the possibility that when ever a new communication pattern is needed, it is relatively easy to be integrated.

The reason we don't follow HPF directly is that during the practice of compiling HPF[2], ``run-time'' support is emphasized in our approach, and we found the level of runtime system can be effectively raised to a programming model. In fact, the new programming style introduced here is a language independent one, it also can be binded with other programming languages such as C/C++ and Fortran.

As Java language is simple, elegant, and more promising, we implemented our prototype based upon this language, and found the efforts are quite rewarding.