might be interesting. 〈Guy Steele on Parallel Programing〉 http://xahlee.org/comp/Guy_Steele_parallel_computing.html
-------------------------------------------------- Guy Steele on Parallel Programing Xah Lee, 2011-02-05 A fascinating talk by the well respected computer scientist Guy Steele. (famously known as one of the author of Scheme Lisp) How to Think about Parallel Programming: Not! (2011-01-14) By Guy Steele. @ http://www.infoq.com/presentations/Thinking-Parallel-Programming The talk is a bit long, at 70 minutes. The first 26 minutes he goes thru 2 computer programs written for 1970's machines. It's quite interesting to see how software on punch card works. For most of us, we never seen a punch card. He actually goes thru it “line by line”, actually “hole by hole”. Watching it, it gives you a sense of how computers are like in the 1970s. At 00:27, he starts talking about “automating resource management”, and quickly to the main point of his talk, as in the title, about what sort of programing paradigms that are good for parallel programing. Here, parallel programing means solving a problem by utilizing multiple CPU or nodes (as in clusters or grid). This is important today, because CPU don't get much faster anymore; instead, each our computer are getting more CPU (multi-core). In the rest 40 min of the talk, he steps thru 2 programs that solves a simple problem of splitting a sentence into words. First program is typical sequential style, using do-loop (accumulator). The second program is written in his language Fortress, using functional style. He then summarizes a few key problems with traditional programing patterns, and introduces a few critical programing patterns that he thinks is critical for programing languages to automate parallel computing. In summary, as a premise, he believes that programers should not worry about parallelism at all, but the programing language should automatically do it. Then, he illustrates that there are few programing patterns that we must stop using, because if you do write your code in such paradigm, then it would be very hard to parallelize the code, either manually or by machine AI. If you are a functional programer and read FP news in the last couple of years, his talk doesn't cover much new. However, i find it very interesting, because: * ① This is the first time i see Guy Steele talk. He talks slightly fast. Very bright guy. * ② The detailed discussion of punch card code on 1970's machine is quite a eye-opener for those of us who's not in that era. * ③ You get to see Fortress code, and its use of fancy unicode chars. * ④ Thru the latter half of talk, you get a concrete sense of some critical “do's ＆ don'ts” in coding paradigms about what makes automated parallel programing possible or impossible. In much of 2000s, i did not understand why compilers couldn't just automatically do parallelism. I thought about it in 2009, and realized why. See: Why Must Software Be Rewritten For Multi-Core Processors?. -------------------- Parallel Computing vs Concurrency Problems Note that parallel programing and concurrency problem are not the same thing. Parallel programing is about writing code that can use multiple CPU. Concurrency problems is about problems of concurrent computations using the same resource or time (e.g. race condition, file locking). See: Parallel computing ◇ Concurrency (computer science) -------------------- Fortress ＆ Unicode It's interesting that Fortress language freely uses unicode chars. For example, list delimiters are not the typical {} or [], but the unicode angle bracket 〈〉. (See: Matching Brackets in Unicode.) It also uses the circle plus ⊕ as operator. (See: Math Symbols in Unicode.) I really appreciate such use of unicode. The tradition of sticking to the 95 chars in ASCII of 1960s is extremely limiting. It creates complex problems manifested in: * String Escape mechanism (C's “\n”, widely adopted.) * Complex delimiters (Python's triple quotes and perl's variable delimiters q() q[] q{} m//, and heredoc. (See: Strings in Perl and Python ◇ Heredoc mechanism in PHP and Perl.) * Crazy leaning toothpick syndrome, especially bad in emacs regex. * Complexities in character representation (See: Emacs's Key Notations Explained (/r, ^M, C-m, RET, <return>, M-, meta) ◇ HTML entities problems. See: HTML Entities, Ampersand, Unicode, Semantics.) * URL Percent Encoding problems and complexities: Javascript Encode URL, Escape String All these problems occur because we are jamming so many meanings into about 20 symbols in ASCII. See also: * Computer Language Design: Strings Syntax * HTML6: Your JSON and SXML Simplified Was this page useful to you? Also, almost all of today's languages do not support unicode in function or variable names, so you can forget about using unicode in variable names (e.g. α=3) or function names (e.g. “lambda” as “λ” or “function” as “ƒ”), or defining your own operators (e.g. “⊕”). (Exceptions i know works well in practice are: Mathematica, Javascript, Java, Emacs Lisp. See: Unicode Support in Ruby, Perl, Python, Emacs Lisp.) Xah ∑ http://xahlee.org/ -- http://mail.python.org/mailman/listinfo/python-list
