# HostConnections.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.conn.routing.HttpRoute;
    import org.apache.http.nio.NHttpClientConnection;
    import org.apache.http.protocol.ExecutionContext;
    import org.apache.http.protocol.HttpContext;
    import org.apache.synapse.transport.http.conn.SynapseHTTPRequestFactory;
    import org.apache.synapse.transport.passthru.PassThroughConstants;
    import org.apache.synapse.transport.passthru.config.ConnectionTimeoutConfiguration;

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

    /**
     * This stores connections for a particular host + port.
     */
    public class HostConnections {
        private static final Log log = LogFactory.getLog(HostConnections.class);
        /**
         * route
         */
        private final HttpRoute route;
        /**
         * maximum number of connections allowed for this host + port
         */
        private final int maxSize;
        /**
         * number of awaiting connections
         */
        private int pendingConnections;
        /**
         * connection idle time for connection removal
         */
        private int connectionIdleTime;
        /**
         * maximum life span of a connection
         */
        private int maximumConnectionLifeSpan;

        /**
         * time allocated to avoid a connection being used at the moment it is being closed or timed out
         */
        private int connectionGraceTime;

        /**
         * list of free connections available
         */
        private List<NHttpClientConnection> freeConnections = new ArrayList<NHttpClientConnection>();
        /**
         * list of connections in use
         */
        private List<NHttpClientConnection> busyConnections = new ArrayList<NHttpClientConnection>();

        private Lock lock = new ReentrantLock();

        public HostConnections(HttpRoute route, int maxSize) {
            if (log.isDebugEnabled()) {
                log.debug("Creating new connection pool: " + route);
            }
            this.route = route;
            this.maxSize = maxSize;
        }

        public HostConnections(HttpRoute route, int maxSize, ConnectionTimeoutConfiguration
                connectionTimeoutConfiguration) {

            if (log.isDebugEnabled()) {
                log.debug("Creating new connection pool: " + route);
            }
            this.route = route;
            this.maxSize = maxSize;

            this.connectionIdleTime = connectionTimeoutConfiguration.getConnectionIdleTime();
            this.maximumConnectionLifeSpan = connectionTimeoutConfiguration.getMaximumConnectionLifeSpane();
            this.connectionGraceTime = connectionTimeoutConfiguration.getConnectionGraceTime();
        }

        /**
         * Get a connection for the host:port
         *
         * @return a connection
         */
        public NHttpClientConnection getConnection() {
            lock.lock();
            try {
                while (!freeConnections.isEmpty()) {
                    if (log.isDebugEnabled()) {
                        log.debug("Returning an existing free connection " + route);
                    }
                    NHttpClientConnection conn = freeConnections.get(0);
                    long currentTime = System.currentTimeMillis();
                    long connectionInitTime = (Long) conn.getContext().getAttribute(PassThroughConstants.
                                                                                            CONNECTION_INIT_TIME);
                    long expiryTime = (Long) conn.getContext().getAttribute(PassThroughConstants.
                            CONNECTION_EXPIRY_TIME);
                    if (isMaximumLifeSpanExceeded(currentTime, connectionInitTime) ||  currentTime >= expiryTime
                            || conn.isStale()) {
                        freeConnections.remove(conn);
                        try {
                            conn.shutdown();
                        } catch (IOException io) {
                            log.error("Error occurred while shutting down connection." + io.getMessage(), io);
                        }
                    } else {
                        freeConnections.remove(conn);
                        busyConnections.add(conn);
                        return conn;
                    }
                }
            } finally {
                lock.unlock();
            }
            return null;
        }

        private boolean isMaximumLifeSpanExceeded(long currentTime, long connectionInitTime) {
            if (maximumConnectionLifeSpan > 0 && currentTime > maximumConnectionLifeSpan + connectionInitTime) {
                if (log.isDebugEnabled()) {
                    log.debug("Connection has been persisted for " + (currentTime - connectionInitTime)
                                      + " milliseconds where the maximum connection life span is " +
                                      maximumConnectionLifeSpan + " milliseconds.");
                }
                return true;
            }
            return false;
        }

        public void release(NHttpClientConnection conn) {
            conn.getMetrics().reset();
            HttpContext ctx = conn.getContext();
            ctx.removeAttribute(ExecutionContext.HTTP_REQUEST);
            ctx.removeAttribute(ExecutionContext.HTTP_RESPONSE);
            ctx.setAttribute(PassThroughConstants.CONNECTION_EXPIRY_TIME, getExpiryTime(conn));
            ctx.removeAttribute(SynapseHTTPRequestFactory.ENDPOINT_URL);
            ctx.removeAttribute(PassThroughConstants.REQUEST_MESSAGE_CONTEXT);
            ctx.removeAttribute(PassThroughConstants.RESPONSE_MESSAGE_CONTEXT);
            lock.lock();
            try {
                if (busyConnections.remove(conn)) {
                    freeConnections.add(conn);
                } else {
                    log.error("Attempted to releaseConnection connection not in the busy list");
                }
            } finally {
                lock.unlock();
            }
        }

        private long getExpiryTime(NHttpClientConnection connection) {

            long expiryTime = System.currentTimeMillis();

            Object keepAlive = connection.getContext().
                    getAttribute(PassThroughConstants.CONNECTION_KEEP_ALIVE_TIME_OUT);
            if (keepAlive != null) {
                int keepAliveTimeout = (int) keepAlive;
                expiryTime = expiryTime + keepAliveTimeout - this.connectionGraceTime;
            } else {
                expiryTime = expiryTime + this.connectionIdleTime;
            }
            if (log.isDebugEnabled()) {
                log.debug("Expiry time set for connection: " + expiryTime + " milliseconds");
            }
            return expiryTime;
        }

        public void forget(NHttpClientConnection conn) {
            lock.lock();
            try {
                if (!freeConnections.remove(conn)) {
                    busyConnections.remove(conn);
                }
            } finally {
                lock.unlock();
            }
        }

        public void addConnection(NHttpClientConnection conn) {
            if (log.isDebugEnabled()) {
                log.debug("New connection " + route + " is added to the free list");
            }
            lock.lock();
            try {
                pendingConnections--;
                conn.getContext().setAttribute(PassThroughConstants.CONNECTION_INIT_TIME, System.currentTimeMillis());
                busyConnections.add(conn);
            } finally {
                lock.unlock();
            }
        }

        /**
         * Indicates that a connection has been successfully established with a remote server
         * as notified by the session request call back.
         */
        public synchronized void pendingConnectionSucceeded() {
            lock.lock();
            try {
                pendingConnections--;
            } finally {
                lock.unlock();
            }
        }

        /**
         * Keep track of the number of times connections to this host:port has failed
         * consecutively
         */
        public void pendingConnectionFailed() {
            lock.lock();
            try {
                pendingConnections--;
            } finally {
                lock.unlock();
            }
        }

        public HttpRoute getRoute() {
            return route;
        }

        public boolean checkAndIncrementPendingConnections() {
            lock.lock();
            int totalConnections = busyConnections.size() + pendingConnections;
            try {
                if (totalConnections < maxSize) {
                    //We are expecting that this check is made if and only if in the state where new connection is added
                    pendingConnections++;
                }
                return totalConnections < maxSize;
            } finally {
                lock.unlock();
            }
        }
    }