# SourceConnections.java

    /**
     *  Copyright (c) 2009, WSO2 Inc. (http://www.wso2.org) All Rights Reserved.
     *
     *  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 org.apache.synapse.transport.passthru.connections;

    import org.apache.commons.logging.Log;
    import org.apache.commons.logging.LogFactory;
    import org.apache.http.nio.NHttpServerConnection;
    import org.apache.http.protocol.HttpContext;
    import org.apache.synapse.transport.passthru.PassThroughConstants;
    import org.apache.synapse.transport.passthru.SourceContext;

    import java.io.IOException;
    import java.util.ArrayList;
    import java.util.List;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;

    /**
     * Keeps track of the connections coming in to the transport.
     */
    public class SourceConnections {
        private static Log log = LogFactory.getLog(SourceConnections.class);

        /** The pool of connections in use */
        private volatile List<NHttpServerConnection> busyConnections = new ArrayList<NHttpServerConnection>();

        /** The pool of connections that are not being used */
        private volatile List<NHttpServerConnection> freeConnections = new ArrayList<NHttpServerConnection>();

        /** Lock for synchronizing the access to the pools */
        private final Lock lock = new ReentrantLock();

        /**
         * Add a connection to the pool.
         *
         * @param conn connection to be added
         */
        public void addConnection(NHttpServerConnection conn) {
            lock.lock();
            try {
                freeConnections.add(conn);
            } finally {
                lock.unlock();
            }
        }

        /**
         * This method should be called when ever a connection being used for processing
         * a request-response.
         *
         * @param conn the connection to be used
         */
        public void useConnection(NHttpServerConnection conn) {
            lock.lock();
            try {
                boolean freeConnection = freeConnections.remove(conn);
                if (freeConnection) {
                    busyConnections.add(conn);
                } else {
                    if (busyConnections.contains(conn)) {
                        throw new IllegalStateException("The connection is busy. " +
                                "Cannot use it for new request");
                    } else {
                        throw new IllegalStateException("Trying to use a connection " +
                                "which is not in free connections " + conn);
                    }
                }
            } finally {
                lock.unlock();
            }
        }

        /**
         * This method should be called after a connection is being used for a request-response.
         *
         * @param conn the connection being used
         */
        public void releaseConnection(NHttpServerConnection conn) {

            removeAttributes(conn);
            lock.lock();
            try {
                SourceContext.get(conn).reset();

                if (busyConnections.remove(conn)) {
                    freeConnections.add(conn);
                } else {
                    if (log.isDebugEnabled()) {
                        log.debug("Trying to finish using a connection " +
                                "which is not in busy connections " + conn);
                    }
                }
            } finally {
                lock.unlock();
            }
        }

        /**
         * Removes the attributes from the http context of the connection
         *
         * @param connection connection object
         */
        private void removeAttributes(NHttpServerConnection connection) {

            HttpContext ctx = connection.getContext();
            ctx.removeAttribute(PassThroughConstants.REQUEST_MESSAGE_CONTEXT);
            ctx.removeAttribute(PassThroughConstants.RESPONSE_MESSAGE_CONTEXT);
        }

    	/**
    	 * Shutdown a connection
    	 *
    	 * @param conn the connection that needs to be shut down
    	 */
    	public void shutDownConnection(NHttpServerConnection conn) {
    		shutDownConnection(conn, false);
    	}

        /**
         * Shutdown a connection
         *
         * @param conn the connection that needs to be shut down
         * @param isError whether an error is causing this shutdown of the connection
         *                It is very important to set this flag correctly.
         *                When an error causing the shutdown of the connections we should not
         *                release associated writer buffer to the pool as it might lead into
         *                situations like same buffer is getting released to both source and target
         *                buffer factories
         */
        public void shutDownConnection(NHttpServerConnection conn, boolean isError) {
            if (log.isDebugEnabled()) {
                log.debug("Shutting down connection forcefully " + conn);
            }
            lock.lock();
            try {
                SourceContext.get(conn).reset(isError);

                if (!busyConnections.remove(conn)) {
                    freeConnections.remove(conn);
                }

                try {
                    conn.shutdown();
                } catch (IOException ignored) {
                }
            } finally {
                lock.unlock();
            }
        }

        /**
         * Close a connection gracefully.
         *
         * @param conn the connection that needs to be closed.
         */
        public void closeConnection(NHttpServerConnection conn) {
            closeConnection(conn, false);
        }

        /**
         * Close a connection gracefully.
         *
         * @param conn the connection that needs to be closed.
         * @param isError  whether an error is causing the shutdown of the connection.
         *                 When as error is causing a close of a connection we should
         *                 not release the associated buffers into the pool.
         */
        public void closeConnection(NHttpServerConnection conn, boolean isError) {
            if (log.isDebugEnabled()) {
                log.debug("Shutting down connection forcefully " + conn);
            }
            lock.lock();
            try {
                SourceContext.get(conn).reset(isError);

                if (!busyConnections.remove(conn)) {
                    freeConnections.remove(conn);
                }

                try {
                    conn.close();
                } catch (IOException ignored) {
                }
            } finally {
                lock.unlock();
            }
        }

        public void destroy() {
            for (NHttpServerConnection conn : freeConnections) {
                shutDownConnection(conn);
            }

            // for all the busy connections we have to notify that their cannot
            // be anymore requests over them
            for (NHttpServerConnection conn : busyConnections) {
                SourceContext.get(conn).setShutDown(true);
            }
        }
    }