concur1

This gives sample Java and Scala code for the first article in my JVM Concurrency series on IBM developerWorks. The project uses a Maven build, so just do the usual mvn clean install to get everything to a working state. The code is all in the com.sosnoski.concur.article1 package, but is split between main/java and main/scala trees. The core code, including the test launcher (TimedTest), is in the Scala tree.

The test/java and test/scala trees include some basic unit tests for the edit distance calculations.

The data directory contains the list of known words, and a list of misspelled words paired with the corrected spellings. The limited list of known words included does not contain all the correct spellings of the misspelled words, so many of the words will not be found - but that's fine, as long as the same ones are always either found or not found. The list of known words was generated using Spell Checking Oriented Word Lists (SCOWL) 7.1: http://wordlist.sourceforge.net/ The list of misspelled words are a randomized selection from http://en.wikipedia.org/wiki/Wikipedia:Lists_of_common_misspellings/For_machines

The timing test code in the Scala TimingTestBase class runs 10 passes over the data, with 3 second pauses between passes to let the JVM settle. It prints the elapsed time and number of correct matches found on each pass, along with the processing rate in terms of misspelled words per second. At the end of the 10 passes it ends with a summary of the test case and the best time from any pass.

To run timing tests of the two Java and four Scala edit distance code variations use mvn scala:run -Dlauncher={name} -DaddArgs={block size}, where {name} selects the test code:

1. basepool - Simple Java thread pool, with thread count set to number of available cores (ThreadPoolDistance class)
2. forkjoin - Java ForkJoinPool with recursive task splitting (ForkJoinDistance class)
3. parcol - Scala using parallel collection (ParallelCollectionDistance class)
4. dirblock - Scala using default ExecutionContext with (DirectBlockingDistance class)
5. futurefold - Scala using default ExecutionContext with Future.fold helper method (FutureFoldDistance class)
6. recursplit - Scala using Java ForkJoinPool with recursive splitting of futures (RecursiveSplitDistance class)

and {block size} is the number of known words to include in each calculation task.

You can import the project into ScalaIDE with the standard Maven project import handling.

Closure performance code

Besides the code discussed in the article, I've added ClosureTest.scala with some microbenchmark code for checking performance of Scala closures. This didn't really show much of interest, but if you want to try it out you can use the Maven launcher target closures to run it.

I also added a third variation of the Scala editDistance method, this one using a local iterate method instead of the Range.foreach used by the idiomatic Scala code (as the translation of the for (i <- 0 to x) constructs). On the Oracle Java 7 64-bit JVM this variation delivers about 85% of the performance of the tail-recursion code (vs. about 45% for the idiomatic Scala).