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Core Parts of Axis2. This includes Axis2 engine, Client API, Addressing support, etc.,
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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you 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 org.apache.axis2.transport.nhttp;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.http.HttpHost;
import org.apache.http.nio.NHttpClientConnection;
import org.apache.http.protocol.ExecutionContext;

import java.io.IOException;
import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

public class ConnectionPool {

    private static final Log log = LogFactory.getLog(ConnectionPool.class);

    /** A map of available connections for reuse. The key selects the host+port of the
     * connection and the value contains a List of available connections to destination
     */
    private static Map connMap = Collections.synchronizedMap(new HashMap());

    public static NHttpClientConnection getConnection(String host, int port) {

        String key = host + ":" + Integer.toString(port);
        List connections = (List) connMap.get(key);

        if (connections == null || connections.isEmpty()) {
            if (log.isDebugEnabled()) {
                log.debug("No connections available for reuse");
            }
            return null;

        } else {
            NHttpClientConnection conn = null;

            synchronized (connections) {
                while (!connections.isEmpty()) {
                    conn = (NHttpClientConnection) connections.remove(0);

                    if (conn.isOpen()) {
                        if (log.isDebugEnabled()) {
                            log.debug("A connection to host : " + host + " on port : " +
                                port + " is available in the pool, and will be reused");
                        }
                        return conn;
                    } else {
                        if (log.isDebugEnabled()) {
                            log.debug("closing stale connection");
                        }
                        try {
                            conn.close();
                        } catch (IOException ignore) {
                        }
                    }
                }
            }
            return null;
        }
    }

    public static void release(NHttpClientConnection conn) {

        HttpHost host = (HttpHost) conn.getContext().getAttribute(
            ExecutionContext.HTTP_TARGET_HOST);
        String key = host.getHostName() + ":" + Integer.toString(host.getPort());

        List connections = (List) connMap.get(key);
        if (connections == null) {
            synchronized(connMap) {
                // use double locking to make sure
                connections = (List) connMap.get(key);
                if (connections == null) {
                    connections = Collections.synchronizedList(new LinkedList());
                    connMap.put(key, connections);
                }
            }
        }

        connections.add(conn);

        log.debug("Released a connection to host: " + host.getHostName() + " on port : " +
            host.getPort() + " to the connection pool of current size : " + connections.size());
    }
}