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The ability to debug a program at the same conceptual level as it was written is crucial to development of high-quality, high-performace parallel programs. In the case of ZPL, this requires a debug tool capable of supporting source-level debugging, but more specifically Z-Level debugging: complete support for the abstract parallel machine defined by the programming language.

As mentioned in Section gif, ZPL control flow is conceptually implemented on the CTA controller, and hence has sequential semantics. The individual statements, however, are executed by n independent threads, where n is the number of elements in the current region. (In reality, of course, these threads exist only as mloops on the nodes of the CTA.) This is the Z-Level, and is supported by ZEE , the ZPL DEBUGGER .

Steve McLaughry
Fri May 30 15:48:07 PDT 1997