Question

I am using a third party library to do hand evaluation of 7 card poker hands. The method evaluate in this library is declared as public static and I believe it alters some global static arrays within the class. The problem I have is that as I am doing an enumeration algorithm of about 10m enumerations I want to parallelize it, therefore I created FutureTasks which each which evaluate a fraction of the 10m evaluations. The error I am getting is:

java.util.concurrent.ExecutionException: java.lang.ArrayIndexOutOfBoundsException: -2147483648
    at java.util.concurrent.FutureTask$Sync.innerGet(Unknown Source)
    at java.util.concurrent.FutureTask.get(Unknown Source)

Which from what I gather from Google searches is caused when attempting to retrieve the result of a task that aborted by throwing an exception.

Is there some way to make this static method thread safe, like each thread making a its own copy of the global static arrays that are being edited?

Thanks

Answer 1

Create a singleton instance wrapper for the library with a synchronized method decoration on the evaluate method

public final class SynchronizedHandEvaluator {
    private static final SynchronizedHandEvaluator INSTANCE = new SynchronizedHandEvaluator();
    public static final getInstance() {
      return INSTANCE;
    }
    private SynchronizedHandEvaluator() { }

    public synchronized int evaluate(Card[] hand) {
        return ExternalLibrary.evaluate(hand);
    }
}


// then just use the wrapper as you would expect
int result = SynchronizedHandEvaluator.getInstance().evaluate(hand);