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Overview

An HPF program may need to call a procedure implemented in a different programming model or in a different programming language. A procedure's programming model might provide:

• a single logical thread-of-control where one copy of the procedure is conceptually executing and there is a single locus of control within the program text; this model is called global when the underlying target hardware has (potentially) multiple processors or memories and is called serial when the underlying target hardware is treated as a uniprocessor (or a single node in a multiprocessor),
• multiple threads-of-control, one per processor, each thread executing the same procedure; this model is called local or, more generally, SPMD (Single Program, Multiple Data), or
• some other model, not discussed here, such as multiple threads-of-control, perhaps with dynamic assignment of loop iterations to processors or explicit dynamic process forking, where there is, at least initially upon invocation, one copy of the procedure that is conceptually executing but that may spawn multiple loci of control, possibly changing in number over time, within the program text.

A programming language provides a specific syntax (language features), semantics (meanings), and pragmatics (purposes). Examples of programming languages include Fortran (an ANSI and ISO standard--the most recent revision is expected to be approved by 1997), HPF (a specification of extensions and restrictions to Fortran), Fortran 77 (a previous ANSI and ISO standard), C, C++, Java, Visual Basic, and COBOL.

A program unit's language and model, when taken together, constitute its extrinsic kind. This extrinsic kind may be specified explicitly by an extrinsic-prefix or implicitly by the selection of a compiler and its invocation with a particular set of compiler options. Thus, one might view the compiler as providing a host scoping unit as defined by Fortran. For example, a program unit compiled by an HPF compiler will be of extrinsic kind HPF. Alternatively, its extrinsic kind may be specified explicitly by an extrinsic-prefix such as EXTRINSIC(HPF) or EXTRINSIC(LANGUAGE="0DHPF"0D,MODEL="0DGLOBAL"0D) .