From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,83e2886f2be41271 X-Google-Attributes: gid103376,public From: John Harbaugh Subject: Re: Tasks in Gnat3.05 for Dos? Date: 1996/07/24 Message-ID: <31F69523.63AB@bunsen.ds.boeing.com>#1/1 X-Deja-AN: 169967225 sender: nntp@bcstec.ca.boeing.com (NNTP News Access) x-nntp-posting-host: 137.136.74.64 references: <4sev09$dik@masala.cc.uh.edu> <4su2km$dt4@masala.cc.uh.edu> <31F3E4E7.13E4@bunsen.ds.boeing.com> content-type: text/plain; charset=us-ascii organization: Employee Training, Boeing D&SG mime-version: 1.0 newsgroups: comp.lang.ada x-mailer: Mozilla 2.0 (Win95; I; 16bit) Date: 1996-07-24T00:00:00+00:00 List-Id: Robert A Duff wrote: > > In article <31F3E4E7.13E4@bunsen.ds.boeing.com>, > John Harbaugh wrote: > >In their excellent book "Concurrency In Ada" Burns and Welling make a useful > >distinction between parallelism and concurrency: > > > >"Two processes are said to be executing in parallel if at any instant they > >are both executing... By comparison, two processes are said to be concurrent > >if they have the potential for executing in parallel." > > Can you write a test program that can tell the difference? > > - Bob The distinction is useful but not rigorous. I do not claim to speak for the authors, but my understanding is that they want the reader to think of program structure as independent of hardware architecture. A correct concurrent design will work on one or many processors; a design which assumes a multi-processor architecture may not execute correctly on a single-processor machine (at least not without some kludge like time slicing). In a recent post, Dr. Feldman related his experience with re-hosting a transportations simulation. The portability was, I suspect, the result of understanding the inherent concurrency of the problem. In other words, concurrency is an attribute of the problem space. Parallelism is an attribute of the solution space. - John Harbaugh The Boeing Company