"Parallel.For" for Java?

Question

I was wondering if there is a Parallel.For equivalent to the .net version for Java?

If there is could someone please supply an example? thanks!

Answer 1

I guess the closest thing would be:

ExecutorService exec = Executors.newFixedThreadPool(SOME_NUM_OF_THREADS); try {     for (final Object o : list) {         exec.submit(new Runnable() {             @Override             public void run() {                 // do stuff with o.             }         });     } } finally {     exec.shutdown(); } 

Based on TheLQ's comments, you would set SUM_NUM_THREADS to Runtime.getRuntime().availableProcessors();

Edit: Decided to add a basic "Parallel.For" implementation

public class Parallel {     private static final int NUM_CORES = Runtime.getRuntime().availableProcessors();      private static final ExecutorService forPool = Executors.newFixedThreadPool(NUM_CORES * 2, new NamedThreadFactory("Parallel.For"));      public static <T> void For(final Iterable<T> elements, final Operation<T> operation) {         try {             // invokeAll blocks for us until all submitted tasks in the call complete             forPool.invokeAll(createCallables(elements, operation));         } catch (InterruptedException e) {             e.printStackTrace();         }     }      public static <T> Collection<Callable<Void>> createCallables(final Iterable<T> elements, final Operation<T> operation) {         List<Callable<Void>> callables = new LinkedList<Callable<Void>>();         for (final T elem : elements) {             callables.add(new Callable<Void>() {                 @Override                 public Void call() {                     operation.perform(elem);                     return null;                 }             });         }          return callables;     }      public static interface Operation<T> {         public void perform(T pParameter);     } } 

Example Usage of Parallel.For

// Collection of items to process in parallel Collection<Integer> elems = new LinkedList<Integer>(); for (int i = 0; i < 40; ++i) {     elems.add(i); } Parallel.For(elems,   // The operation to perform with each item  new Parallel.Operation<Integer>() {     public void perform(Integer param) {         System.out.println(param);     }; }); 

I guess this implementation is really more similar to Parallel.ForEach

Edit I put this up on GitHub if anyone is interested. Parallel For on GitHub

Answer 2

MLaw's solution is a very practical Parallel.ForEach. I added a bit modification to make a Parallel.For.

public class Parallel { static final int iCPU = Runtime.getRuntime().availableProcessors();  public static <T> void ForEach(Iterable <T> parameters,                    final LoopBody<T> loopBody) {     ExecutorService executor = Executors.newFixedThreadPool(iCPU);     List<Future<?>> futures  = new LinkedList<Future<?>>();      for (final T param : parameters)     {         Future<?> future = executor.submit(new Runnable()         {             public void run() { loopBody.run(param); }         });          futures.add(future);     }      for (Future<?> f : futures)     {         try   { f.get(); }         catch (InterruptedException e) { }          catch (ExecutionException   e) { }              }      executor.shutdown();      }  public static void For(int start,                    int stop,                final LoopBody<Integer> loopBody) {     ExecutorService executor = Executors.newFixedThreadPool(iCPU);     List<Future<?>> futures  = new LinkedList<Future<?>>();      for (int i=start; i<stop; i++)     {         final Integer k = i;         Future<?> future = executor.submit(new Runnable()         {             public void run() { loopBody.run(k); }         });              futures.add(future);     }      for (Future<?> f : futures)     {         try   { f.get(); }         catch (InterruptedException e) { }          catch (ExecutionException   e) { }              }      executor.shutdown();      } }  public interface LoopBody <T> {     void run(T i); }  public class ParallelTest { int k;    public ParallelTest() {     k = 0;     Parallel.For(0, 10, new LoopBody <Integer>()     {         public void run(Integer i)         {             k += i;             System.out.println(i);                   }     });     System.out.println("Sum = "+ k); }  public static void main(String [] argv) {     ParallelTest test = new ParallelTest(); } }