Dr. Dobb's Journal - February 2009 - (Page 34)

d02kim_p3db 12/12/08 9:53 AM Page 34 State of the Art PARALLEL LINQ By default, the original sequence order is not maintained when you invoke a PLINQ query detract from performance speedup. The net effect is that having two or four processors do not necessarily mean that your code will run two times or four times faster, respectively. Handling Concurrency Exceptions Parallel extensions always throw a single AggregateException object. AggregateException contains an inner collection property named InnerExceptions. If individual exceptions were thrown, then it would be easier for programmers to miss one or the other possible catch blocks. However, using a single exception class makes debugging a little harder because the break happens at the location of the AggregateException catch block rather than the location of the underlying exception. The net result is that debugging exceptions require you to do some extra detective work by examining the AggregateException.InnerExceptions collection. Sometimes you can navigate the stack trace to figure out where things went wrong, but the Visual Studio call stack is not 100-percent navigable. Tips for Enhancing Performance I just finished re-reading Dan Brown’s Digital Fortress, which is about the NSA, cryptography, spies, and secrets. The book includes some examples of simple word ciphers and references to the World War II Enigma cipher machine. This led me to Listing Two (available online; see “Resource Center,” page 4), which reads the text of a book from Gutenberg.org and uses a simple cipher to encrypt the text. The sample text is from Lewis Carroll’s Alice’s Adventures in Wonderland and uses a simple substitution cipher to encrypt the text. At 29,000 words, the document is not huge, but if you run the sample code, you see the parallel encryption loop is significantly faster than the sequential loop. Listing Two uses the WebClient class to download the text of Alice in Wonderland (referring to the Cypher.Demo method). The text of the story is split into lines— characters actually resulted in poorer performance than the sequential version— and encrypted. The text is encrypted three 34 Dr. Dobb’s Journal l www.ddj.com l February 2009 http://www.Gutenberg.org http://www.programmingresearch.com http://www.programmingresearch.com http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - February 2009

Dr. Dobb's Journal - February 2009 Contents Friday Night Fish Fry Alia Vox Developer Diaries Conversations Computing in the Clouds Software Development in the Cloud Videos and Oracle Forms 10g Parallel LINQ Decoupling C Header Files Effective Concurrency Disciplined Agility Swaine’s Flames

Dr. Dobb's Journal - February 2009

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