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Async Http Client library purpose is to allow Java applications to easily execute HTTP requests and asynchronously process the HTTP responses.

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/*
 * Copyright (c) 2014 AsyncHttpClient Project. All rights reserved.
 *
 * This program is licensed to you under the Apache License Version 2.0,
 * and you may not use this file except in compliance with the Apache License Version 2.0.
 * You may obtain a copy of the Apache License Version 2.0 at
 *     http://www.apache.org/licenses/LICENSE-2.0.
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the Apache License Version 2.0 is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the Apache License Version 2.0 for the specific language governing permissions and limitations there under.
 */
package com.ning.http.client.providers.netty.channel;

import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelFuture;
import org.jboss.netty.channel.group.ChannelGroup;
import org.jboss.netty.channel.group.ChannelGroupFuture;
import org.jboss.netty.channel.group.DefaultChannelGroup;
import org.jboss.netty.channel.group.DefaultChannelGroupFuture;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.ArrayList;
import java.util.Collection;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * Extension of {@link DefaultChannelGroup} that's used mainly as a cleanup container, where {@link #close()} is only
 * supposed to be called once.
 *
 * @author Bruno de Carvalho
 */
public class CleanupChannelGroup extends DefaultChannelGroup {

    private final static Logger logger = LoggerFactory.getLogger(CleanupChannelGroup.class);

    // internal vars --------------------------------------------------------------------------------------------------

    private final AtomicBoolean closed;
    private final ReentrantReadWriteLock lock;

    // constructors ---------------------------------------------------------------------------------------------------

    public CleanupChannelGroup() {
        this.closed = new AtomicBoolean(false);
        this.lock = new ReentrantReadWriteLock();
    }

    public CleanupChannelGroup(String name) {
        super(name);
        this.closed = new AtomicBoolean(false);
        this.lock = new ReentrantReadWriteLock();
    }

    // DefaultChannelGroup --------------------------------------------------------------------------------------------

    @Override
    public ChannelGroupFuture close() {
        this.lock.writeLock().lock();
        try {
            if (!this.closed.getAndSet(true)) {
                // First time close() is called.
                return super.close();
            } else {
                Collection futures = new ArrayList<>();
                logger.debug("CleanupChannelGroup Already closed");
                return new DefaultChannelGroupFuture(ChannelGroup.class.cast(this), futures);
            }
        } finally {
            this.lock.writeLock().unlock();
        }
    }

    @Override
    public boolean add(Channel channel) {
        // Synchronization must occur to avoid add() and close() overlap (thus potentially leaving one channel open).
        // This could also be done by synchronizing the method itself but using a read lock here (rather than a
        // synchronized() block) allows multiple concurrent calls to add().
        this.lock.readLock().lock();
        try {
            if (this.closed.get()) {
                // Immediately close channel, as close() was already called.
                Channels.silentlyCloseChannel(channel);
                return false;
            }

            return super.add(channel);
        } finally {
            this.lock.readLock().unlock();
        }
    }
}