Java tutorial
/* * Copyright 2012-2014 Amazon.com, Inc. or its affiliates. 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. * A copy of the License is located at * * http://aws.amazon.com/apache2.0 * * or in the "license" file accompanying this file. This file 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 com.amazonaws.http; import java.util.ArrayList; import java.util.List; import java.util.concurrent.TimeUnit; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.http.conn.ClientConnectionManager; /** * Daemon thread to periodically check connection pools for idle connections. * <p> * Connections sitting around idle in the HTTP connection pool for too long will * eventually be terminated by the AWS end of the connection, and will go into * CLOSE_WAIT. If this happens, sockets will sit around in CLOSE_WAIT, still * using resources on the client side to manage that socket. Many sockets stuck * in CLOSE_WAIT can prevent the OS from creating new connections. * <p> * This class closes idle connections before they can move into the CLOSE_WAIT * state. * <p> * This thread is important because by default, we disable Apache HttpClient's * stale connection checking, so without this thread running in the background, * cleaning up old/inactive HTTP connections, we'd see more IO exceptions when * stale connections (i.e. closed on the AWS side) are left in the connection * pool, and requests grab one of them to begin executing a request. */ public final class IdleConnectionReaper extends Thread { /** The period between invocations of the idle connection reaper. */ private static final int PERIOD_MILLISECONDS = 1000 * 60 * 1; /** * The list of registered connection managers, whose connections * will be periodically checked and idle connections closed. */ private static final ArrayList<ClientConnectionManager> connectionManagers = new ArrayList<ClientConnectionManager>(); /** * Set to true when shutting down the reaper; Once set to true, this * flag is never set back to false. */ private volatile boolean shuttingDown; /** Singleton instance of the connection reaper. */ private static IdleConnectionReaper instance; /** Shared log for any errors during connection reaping. */ static final Log log = LogFactory.getLog(IdleConnectionReaper.class); /** Private constructor - singleton pattern. */ private IdleConnectionReaper() { super("java-sdk-http-connection-reaper"); setDaemon(true); } /** * Registers the given connection manager with this reaper; * * @return true if the connection manager has been successfully registered; * false otherwise. */ public static synchronized boolean registerConnectionManager(ClientConnectionManager connectionManager) { if (instance == null) { instance = new IdleConnectionReaper(); instance.start(); } return connectionManagers.add(connectionManager); } /** * Removes the given connection manager from this reaper, * and shutting down the reaper if there is zero connection manager left. * * @return true if the connection manager has been successfully removed; * false otherwise. */ public static synchronized boolean removeConnectionManager(ClientConnectionManager connectionManager) { boolean b = connectionManagers.remove(connectionManager); if (connectionManagers.isEmpty()) shutdown(); return b; } private void markShuttingDown() { shuttingDown = true; } @SuppressWarnings("unchecked") @Override public void run() { while (true) { if (shuttingDown) { log.debug("Shutting down reaper thread."); return; } try { Thread.sleep(PERIOD_MILLISECONDS); // Copy the list of managed ConnectionManagers to avoid possible // ConcurrentModificationExceptions if registerConnectionManager or // removeConnectionManager are called while we're iterating (rather // than block/lock while this loop executes). List<ClientConnectionManager> connectionManagers = null; synchronized (IdleConnectionReaper.class) { connectionManagers = (List<ClientConnectionManager>) IdleConnectionReaper.connectionManagers .clone(); } for (ClientConnectionManager connectionManager : connectionManagers) { // When we release connections, the connection manager leaves them // open so they can be reused. We want to close out any idle // connections so that they don't sit around in CLOSE_WAIT. try { connectionManager.closeIdleConnections(60, TimeUnit.SECONDS); } catch (Exception t) { log.warn("Unable to close idle connections", t); } } } catch (Throwable t) { log.debug("Reaper thread: ", t); } } } /** * Shuts down the thread, allowing the class and instance to be collected. * <p> * Since this is a daemon thread, its running will not prevent JVM shutdown. * It will, however, prevent this class from being unloaded or garbage * collected, in the context of a long-running application, until it is * interrupted. This method will stop the thread's execution and clear its * state. Any use of a service client will cause the thread to be restarted. * * @return true if an actual shutdown has been made; false otherwise. */ public static synchronized boolean shutdown() { if (instance != null) { instance.markShuttingDown(); instance.interrupt(); connectionManagers.clear(); instance = null; return true; } return false; } /** * For testing purposes. * Returns the number of connection managers currently monitored by this * reaper. */ static synchronized int size() { return connectionManagers.size(); } }