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Next: 16.3.1 Invoices Up: 16 The Zipcode Message-Passing Previous: G3-Class

16.3 High-Level Primitives

In order to facilitate easier use and the possibility of heterogeneous parallel computers, Zipcode provides a mechanism to pack and unpack buffers and letters. Buffers are unstructured arrays of data provided by the user; they are applicable with buffer-oriented Zipcode commands. Letters are unstructured arrays of data provided by Zipcode based on user specification; they are tied to specific mail contexts and are dynamically allocated and freed.

Pack (gather) and unpack (scatter) are implemented with the use of Zip_Invoices. The analogy is taken from invoices or packing slips used to specify the contents of a postal package. An invoice informs Zipcode what variables are to be associated with a communication operation or communication buffer. This invoice is subsequently used when zip_pack() (zip_unpack()) is called to copy items from the variables specified into (out of) the communication buffer space to be sent (received); this implements gather-on-send- and scatter-on-receive-type semantics. In a heterogeneous environment, pack/unpacking will allow data conversions to take place without user intervention. Users who code with zip_pack()/zip_unpack() will have codes that are guaranteed to work in heterogeneous implementations of Zipcode.

Guy Robinson
Wed Mar 1 10:19:35 EST 1995