Next: DistributionsAlignments, and Up: User Guide for Previous: Encapsulating SPMD Libraries.

Collections. Ver 1.0+

Thread environment classes provide a simple, portable mechanism for a limited form of parallelism. However, a more important abstraction is based on a structure called a concurrent aggregate, or collection.

The motivation is to describe a structure that defines a set of objects of some given type that can be distributed over the memory modules of a parallel system.

The way in which elements of a collection are distributed over processors is determined by a two-step mechanism similar to HPFF Fortran. In the first step, collection elements are mapped to a logical coordinate system. This first mapping is called an alignment and it is defined by an Align class object. A Distribution class object defines the logical coordinate system and the way in which it is mapped to Processors object threads.

The declaration of a collection is specified by a collection type name followed by a type name of the element objects enclosed in angle brackets. The arguments for the three constructors define these collections in terms of alignment and distribution objects.

  collection-name <  element-name >  object( constructor arguments )
For example, suppose we want to create a matrix, A, and two vectors, X and Y, of complex numbers and want to distribute them over processors of a parallel machine. Given a C++ class for complex numbers, Complex, we can build distributed matrix and vector collections by using the pC++ library collection classes DistributedMatrix and DistributedVector as follows:

      DistributedMatrix<Complex>  A(...constructor arguments ...);
      DistributedVector<Complex>  X(...constructor arguments ...);
      DistributedVector<Complex>  Y(...constructor arguments ...);

Mon Nov 21 09:49:54 EST 1994