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The Software Architecture Impact of the Multi-Core Processor Trend

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The Java Developer's Journal has a great article about how software developers are going to be impacted by the industry trend towards multi-core and massively parallel processors. From the article:

As software developers we have enjoyed a long trend of consistent performance improvement from processor technology. In fact, for the last 20 years processor performance has consistently doubled about every two years or so. What would happen in a world where these performance improvements suddenly slowed dramatically or even stopped? Could we continue to build bigger and heavier, feature-rich software? ... The truth is, single threaded performance improvement is likely to see a significant slowdown over the next one to three years. In some cases, single-thread performance may even drop. The long and sustained climb will slow dramatically.

The name of the source magazine notwithstanding, the article is an interesting read even if you aren't a Java shop. As you might guess, the authors don't just leave you with that despairing thought above. The article goes on to explain how we will need to adjust the architecture of our software to continue sustained growth:

... the industry is looking to multi-core and multithreaded processor designs to continue the performance improvement trend. These designs don't look to improve the performance of single threads of execution, but instead to run many and sometimes massive numbers of threads in parallel. ... As a developer, it will be important for you to learn the skills necessary to develop applications that can run with high performance on these increasingly parallel processors. Since single-thread performance isn't likely to improve at historical rates, the developer will have to look to concurrency to improve performance for a given task.

The rest of the article provides an introductory-level overview to strategies for parallel programming, starting with Amdahl's Law:

As you get started with parallel programming, the first rule to become familiar with is Amdahl's Law. Amdahl's Law says that speeding up your program is limited by the part that's not running in parallel. For example, if a profile reveals that 20% of the time is spent in code that can only run sequentially on one processor, then the best speed increase you can possibly get, even with perfect parallelization of the rest of your program is 5x, no matter how many processors you throw at it. Load imbalance is a similar problem. If you've divided your code into N subtasks, the time taken to execute them is not 1/N. Rather the time taken is the maximum of the execution times of the subtasks.

And then flows into concurrency issues and Thread programming, focusing on the Java language constructs for parallel programming. The article wraps up by announcing a new language developed by IBM called X10 which adds higher-level constructs to the Java language specifically for parallel application development. It seeks to simplifiy concurrent programming by providing simplified semantics for managing both concurrent operations and the distribution of data associated with those operations.

X10 can't really be considered an internal DSL because its syntax is not valid Java syntax. It is closer to AspectJ (pre version 5) in that it uses the Java language as a basis and then builds a new, distinct language from there.

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