ForkJoinMain.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveAction;
import java.util.function.Consumer;

public class ForkJoinMain {


	private static List<String> members 
	= Arrays.asList("a", "b", "c"
			,"d", "e", "f"
			,"g", "h", "i"
			,"j", "k", "l");



	public void test(){


		ForkJoinPool forkJoinPool = new ForkJoinPool(4);
		CustomAction<String> task = new CustomAction<>(members, (item)->{

			System.out.println("foreach : " + item + " : "+ Thread.currentThread());
		});

		forkJoinPool.invoke(task);
	}


	public static void main(String[] args) throws InterruptedException {

		new ForkJoinMain().test();

	}


	public class CustomAction<T> extends RecursiveAction {

		private List<T> members;
		private Consumer<T> consumer;

		public CustomAction(List<T> members, Consumer<T> consumer){
			this.members = members;
			this.consumer = consumer;
		}

		@Override
		protected void compute() {

			if(members.size() > 3) {
				List<CustomAction<T>> subTasks = createSubTasks();

				subTasks.forEach(subTask -> {
					subTask.fork();
				});

				
			} else {
				members.forEach(consumer);
			}
		}

		private List<CustomAction<T>> createSubTasks(){

			List<CustomAction<T>> subTasks = new ArrayList<>();


			int half = (members.size() -1 )/2;
			subTasks.add( new CustomAction<>(members.subList(0, half), consumer) );
			subTasks.add( new CustomAction<>(members.subList(half, members.size()), consumer) );

			return subTasks;
		}
	}



}