Loop.java

package cz.cuni.lf1.lge.ThunderSTORM.util;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

/**
 * santiwk at stackoverflow.com
 */
public class Loop {

    private static final int CPUs = Runtime.getRuntime().availableProcessors();
    //private static ExecutorService executor = Executors.newCachedThreadPool();
    private static final ThreadPoolExecutor executor = new ThreadPoolExecutor(CPUs, CPUs, 30, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());

    public static ThreadPoolExecutor getExecutor() {
        return executor;
    }

    static {
        executor.allowCoreThreadTimeOut(true);
    }

    public interface BodyWithIndex {

        void run(int i);
    }

    public static void withIndex(int start, int stop, final BodyWithIndex body) {
        int chunksize = MathProxy.max((stop - start + CPUs - 1) / CPUs, 1);
        int loops = (stop - start + chunksize - 1) / chunksize;
        Future<?>[] futures = new Future<?>[loops];
        int fi = 0;
        for(int i = start; i < stop;) {
            final int lo = i;
            i += chunksize;
            final int hi = (i < stop) ? i : stop;
            futures[fi++] = executor.submit(new Runnable() {
                @Override
                public void run() {
                    for(int i = lo; i < hi; i++) {
                        body.run(i);
                    }
                }
            });
        }
        //gather any exceptions
        RuntimeException t = null;
        Error e = null;
        for(Future<?> f : futures) {
            try {
                f.get();
            } catch(InterruptedException ex) {
            } catch(ExecutionException ex) {
                if(ex.getCause() instanceof RuntimeException) {
                    t = (RuntimeException) ex.getCause();
                }
                if(ex.getCause() instanceof Error) {
                    e = (Error) ex.getCause();
                }
            }
        }
        if(t != null) {
            throw t;
        }
        if(e != null) {
            throw e;
        }
    }

    public static void shutdown() {
        executor.shutdown();
    }
}