IterableBlockingQueue.java

package cj.util.collections;

import java.util.Iterator;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;

/**
 * @author dron
 * This class should be used as an "iterable" by consumers and a queue by producers.
 * Unlike a normal blocking queue, the iterator will BLOCK on hasNext rather than returning false
 * which allows this type to work like a buffer.
 * 
 * Multiple calls to iterator() will return different iterators with the same thread-safe backing data
 * Which would allow multiple consumer threads to share the work generated by any number of producers adding to this queue.
 * 
 * Consumers will continue to iterate until producers call the "done()" method.
 * 
 */
public class IterableBlockingQueue<T> implements  Iterable<T>{
    private Queue<T> queue = new ConcurrentLinkedQueue<T>();
    private boolean isDone=false;

    public void done(){
        isDone=true;
    }
    
    public void add(T object){
    	queue.add(object);
    }
    
	public Integer size() {
		return queue.size();
	}

    @Override
    public Iterator<T> iterator() {
        return new Iterator<T>() {
            @Override
            public boolean hasNext() {            	
					try {
						//TODO: Waiting 300ms is a naive solution to blocking.
						while(queue.isEmpty() && !isDone) Thread.sleep(300);
					} catch (InterruptedException e) {}
                return !(queue.isEmpty() && isDone);
            }

            @Override
            public T next() {
                return queue.remove();
            }

            @Override
            public void remove() {
                queue.remove();
            }
        };
    }


}