package edu.teco.dnd.util;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * Combines multiple FutureNotifiers. If all FutureNotifiers succeed this will succeed as well. If at least one fails this
 * will also be set to be a failure and the cause will be set to the cause of the failed FutureNotifier. If multiple FutureNotifiers
 * fail the cause is set to one of the causes of the failed FutureNotifiers without any guarantee as to which one.
 * 
 * @author Philipp Adolf
 *
 * @param <T> the type of the result of the FutureNotifiers that should be joined
 */
public class JoinedFutureNotifier<T> extends DefaultFutureNotifier<Collection<T>> implements FutureListener<FutureNotifier<T>>{
	/**
	 * The FutureNotifiers that are combined.
	 */
	private final Collection<FutureNotifier<? extends T>> futures;
	
	/**
	 * The number of FutureNotifiers that have not yet finished. Only relevant in the success case.
	 */
	private final AtomicInteger unfinished;
	
	/**
	 * Initializes a new JoinedFutureNotifier.
	 * 
	 * @param futures the FutureNotifiers that should be joined
	 */
	public JoinedFutureNotifier(final Collection<FutureNotifier<? extends T>> futures) {
		this.futures = Collections.unmodifiableSet(new HashSet<FutureNotifier<? extends T>>(futures));
		unfinished = new AtomicInteger(this.futures.size());
		for (FutureNotifier<? extends T> future : this.futures) {
			future.addListener(this);
		}
	}

	@Override
	public synchronized void operationComplete(final FutureNotifier<T> future) {
		if (!isDone()) {
			if (future.isSuccess()) {
				if (unfinished.decrementAndGet() <= 0) {
					final Collection<T> result = new ArrayList<T>();
					for (final FutureNotifier<? extends T> notifier : this.futures) {
						result.add(notifier.getNow());
					}
					setSuccess(result);
				}
			} else {
				setFailure(future.cause());
			}
		}
	}
}

package edu.teco.dnd.util;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * Combines multiple FutureNotifiers. If all FutureNotifiers succeed this will succeed as well. If at least one fails this
 * will also be set to be a failure and the cause will be set to the cause of the failed FutureNotifier. If multiple FutureNotifiers
 * fail the cause is set to one of the causes of the failed FutureNotifiers without any guarantee as to which one.
 * 
 * @author Philipp Adolf
 *
 * @param <T> the type of the result of the FutureNotifiers that should be joined
 */
public class JoinedFutureNotifier<T> extends DefaultFutureNotifier<Collection<T>> implements FutureListener<FutureNotifier<T>>{
	/**
	 * The FutureNotifiers that are combined.
	 */
	private final Collection<FutureNotifier<? extends T>> futures;
	
	/**
	 * The number of FutureNotifiers that have not yet finished. Only relevant in the success case.
	 */
	private final AtomicInteger unfinished;
	
	/**
	 * Initializes a new JoinedFutureNotifier.
	 * 
	 * @param futures the FutureNotifiers that should be joined
	 */
	public JoinedFutureNotifier(final Collection<FutureNotifier<? extends T>> futures) {
		this.futures = Collections.unmodifiableSet(new HashSet<FutureNotifier<? extends T>>(futures));
		final int unfinished = this.futures.size();
		this.unfinished = new AtomicInteger(unfinished);
		if (unfinished <= 0) {
			setSuccess(new ArrayList<T>());
		} else {
			for (FutureNotifier<? extends T> future : this.futures) {
				future.addListener(this);
			}
		}
	}

	@Override
	public synchronized void operationComplete(final FutureNotifier<T> future) {
		if (!isDone()) {
			if (future.isSuccess()) {
				if (unfinished.decrementAndGet() <= 0) {
					final Collection<T> result = new ArrayList<T>();
					for (final FutureNotifier<? extends T> notifier : this.futures) {
						result.add(notifier.getNow());
					}
					setSuccess(result);
				}
			} else {
				setFailure(future.cause());
			}
		}
	}
}

Fix bug with zero FutureNotifiers