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package com.openexchange.ajp13.stable;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.atomic.AtomicBoolean;
import com.openexchange.ajp13.AJPv13Config;

/**
 * {@link AJPv13ConnectionPool} - The AJP connection pool
 * 
 * @author <a href="mailto:thorben.betten@open-xchange.com">Thorben Betten</a>
 */
final class AJPv13ConnectionPool {

    private static final org.apache.commons.logging.Log LOG = org.apache.commons.logging.LogFactory.getLog(AJPv13ConnectionPool.class);

    private static final AtomicBoolean initialized = new AtomicBoolean();

    private static BlockingQueue<AJPv13ConnectionImpl> CONNECTION_QUEUE;

    private AJPv13ConnectionPool() {
        super();
    }

    /**
     * Initializes the AJP connection pool by creating the specified amount of connection instances given through property
     * {@link AJPv13Config#getAJPConnectionPoolSize()}
     */
    static void initConnectionPool() {
        if (!initialized.get()) {
            synchronized (initialized) {
                if (null == CONNECTION_QUEUE) {
                    final int poolSize = AJPv13Config.getAJPConnectionPoolSize();
                    CONNECTION_QUEUE = new ArrayBlockingQueue<AJPv13ConnectionImpl>(poolSize);
                    for (int i = 0; i < poolSize; i++) {
                        CONNECTION_QUEUE.add(new AJPv13ConnectionImpl());
                    }
                    if (LOG.isInfoEnabled()) {
                        LOG.info(new StringBuilder(50).append(poolSize).append(" AJPv13Connection instances created in advance").toString());
                    }
                    initialized.set(true);
                }
            }
        }
    }

    /**
     * Resets the AJP connection pool
     */
    static void resetConnectionPool() {
        if (initialized.get()) {
            synchronized (initialized) {
                if (null != CONNECTION_QUEUE) {
                    CONNECTION_QUEUE.clear();
                    CONNECTION_QUEUE = null;
                    initialized.set(false);
                }
            }
        }
    }

    /**
     * Fetches an existing connection from pool or creates a new instance if none available in pool
     * 
     * @param l The AJP listener which is assigned to returned AJP connection
     * @return A pooled or newly created AJP connection
     */
    static AJPv13ConnectionImpl getAJPv13Connection(final AJPv13Listener l) {
        final AJPv13ConnectionImpl ajpCon = CONNECTION_QUEUE.poll();
        if (ajpCon == null) {
            return new AJPv13ConnectionImpl(l);
        }
        return ajpCon.setListener(l);
    }

    /**
     * Puts given AJP Connection back in pool if there's enough space in queue otherwise the instance is going to be discarded
     * 
     * @param ajpCon The AJP connection which shall be put into pool
     * @return <code>true</code> if AJP connection was successfully put into pool; otherwise <code>false</code>
     */
    static boolean putBackAJPv13Connection(final AJPv13ConnectionImpl ajpCon) {
        if (ajpCon == null) {
            return false;
        }
        return CONNECTION_QUEUE.offer(ajpCon);
    }

}
