ListenableFutureCallbackRegistry.java

/*
 * Copyright 2002-2013 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.xiongyingqi.util.concurrent;

import com.xiongyingqi.util.Assert;

import java.util.LinkedList;
import java.util.Queue;

/**
 * Registry for {@link ListenableFutureCallback} instances.
 * <p>
 * <p>Inspired by {@code com.google.common.util.concurrent.ExecutionList}.
 *
 * @author Arjen Poutsma
 * @since 4.0
 */
public class ListenableFutureCallbackRegistry<T> {

    private final Queue<ListenableFutureCallback<? super T>> callbacks =
            new LinkedList<ListenableFutureCallback<? super T>>();

    private State state = State.NEW;

    private Object result = null;

    private final Object mutex = new Object();


    /**
     * Adds the given callback to this registry.
     *
     * @param callback the callback to add
     */
    @SuppressWarnings("unchecked")
    public void addCallback(ListenableFutureCallback<? super T> callback) {
        Assert.notNull(callback, "'callback' must not be null");

        synchronized (mutex) {
            switch (state) {
                case NEW:
                    callbacks.add(callback);
                    break;
                case SUCCESS:
                    callback.onSuccess((T) result);
                    break;
                case FAILURE:
                    callback.onFailure((Throwable) result);
                    break;
            }
        }
    }

    /**
     * Triggers a {@link ListenableFutureCallback#onSuccess(Object)} call on all added
     * callbacks with the given result
     *
     * @param result the result to trigger the callbacks with
     */
    public void success(T result) {
        synchronized (mutex) {
            state = State.SUCCESS;
            this.result = result;

            while (!callbacks.isEmpty()) {
                callbacks.poll().onSuccess(result);
            }
        }
    }

    /**
     * Triggers a {@link ListenableFutureCallback#onFailure(Throwable)} call on all added
     * callbacks with the given {@code Throwable}.
     *
     * @param t the exception to trigger the callbacks with
     */
    public void failure(Throwable t) {
        synchronized (mutex) {
            state = State.FAILURE;
            this.result = t;

            while (!callbacks.isEmpty()) {
                callbacks.poll().onFailure(t);
            }
        }
    }

    private enum State {NEW, SUCCESS, FAILURE}

}