Java tutorial
/** * 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.curator; import com.google.common.annotations.VisibleForTesting; import org.apache.curator.utils.CloseableUtils; import org.apache.curator.drivers.EventTrace; import org.apache.curator.drivers.OperationTrace; import org.apache.curator.drivers.TracerDriver; import org.apache.curator.ensemble.EnsembleProvider; import org.apache.curator.utils.DebugUtils; import org.apache.curator.utils.ThreadUtils; import org.apache.curator.utils.ZookeeperFactory; import org.apache.zookeeper.KeeperException; import org.apache.zookeeper.WatchedEvent; import org.apache.zookeeper.Watcher; import org.apache.zookeeper.ZooKeeper; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import java.io.Closeable; import java.io.IOException; import java.util.Queue; import java.util.concurrent.ConcurrentLinkedQueue; import java.util.concurrent.atomic.AtomicBoolean; import java.util.concurrent.atomic.AtomicLong; import java.util.concurrent.atomic.AtomicReference; class ConnectionState implements Watcher, Closeable { private static final int MAX_BACKGROUND_EXCEPTIONS = 10; private static final boolean LOG_EVENTS = Boolean.getBoolean(DebugUtils.PROPERTY_LOG_EVENTS); private static final Logger log = LoggerFactory.getLogger(ConnectionState.class); private final HandleHolder zooKeeper; private final AtomicBoolean isConnected = new AtomicBoolean(false); private final EnsembleProvider ensembleProvider; private final int sessionTimeoutMs; private final int connectionTimeoutMs; private final AtomicReference<TracerDriver> tracer; private final Queue<Exception> backgroundExceptions = new ConcurrentLinkedQueue<Exception>(); private final Queue<Watcher> parentWatchers = new ConcurrentLinkedQueue<Watcher>(); private final AtomicLong instanceIndex = new AtomicLong(); private volatile long connectionStartMs = 0; @VisibleForTesting volatile boolean debugWaitOnExpiredEvent = false; ConnectionState(ZookeeperFactory zookeeperFactory, EnsembleProvider ensembleProvider, int sessionTimeoutMs, int connectionTimeoutMs, Watcher parentWatcher, AtomicReference<TracerDriver> tracer, boolean canBeReadOnly) { this.ensembleProvider = ensembleProvider; this.sessionTimeoutMs = sessionTimeoutMs; this.connectionTimeoutMs = connectionTimeoutMs; this.tracer = tracer; if (parentWatcher != null) { parentWatchers.offer(parentWatcher); } zooKeeper = new HandleHolder(zookeeperFactory, this, ensembleProvider, sessionTimeoutMs, canBeReadOnly); } ZooKeeper getZooKeeper() throws Exception { if (SessionFailRetryLoop.sessionForThreadHasFailed()) { throw new SessionFailRetryLoop.SessionFailedException(); } Exception exception = backgroundExceptions.poll(); if (exception != null) { new EventTrace("background-exceptions", tracer.get()).commit(); throw exception; } boolean localIsConnected = isConnected.get(); if (!localIsConnected) { checkTimeouts(); } return zooKeeper.getZooKeeper(); } boolean isConnected() { return isConnected.get(); } void start() throws Exception { log.debug("Starting"); ensembleProvider.start(); reset(); } @Override public void close() throws IOException { log.debug("Closing"); CloseableUtils.closeQuietly(ensembleProvider); try { zooKeeper.closeAndClear(); } catch (Exception e) { ThreadUtils.checkInterrupted(e); throw new IOException(e); } finally { isConnected.set(false); } } void addParentWatcher(Watcher watcher) { parentWatchers.offer(watcher); } void removeParentWatcher(Watcher watcher) { parentWatchers.remove(watcher); } long getInstanceIndex() { return instanceIndex.get(); } @Override public void process(WatchedEvent event) { if (LOG_EVENTS) { log.debug("ConnectState watcher: " + event); } final boolean eventTypeNone = event.getType() == Watcher.Event.EventType.None; if (eventTypeNone) { boolean wasConnected = isConnected.get(); boolean newIsConnected = checkState(event.getState(), wasConnected); if (newIsConnected != wasConnected) { isConnected.set(newIsConnected); connectionStartMs = System.currentTimeMillis(); } } // only wait during tests if (debugWaitOnExpiredEvent && event.getState() == Event.KeeperState.Expired) { waitOnExpiredEvent(); } for (Watcher parentWatcher : parentWatchers) { OperationTrace trace = new OperationTrace("connection-state-parent-process", tracer.get(), getSessionId()); parentWatcher.process(event); trace.commit(); } if (eventTypeNone) handleState(event.getState()); } // only for testing private void waitOnExpiredEvent() { log.debug("Waiting on Expired event for testing"); try { Thread.sleep(1000); } catch (InterruptedException e) { } log.debug("Continue processing"); } EnsembleProvider getEnsembleProvider() { return ensembleProvider; } private synchronized void checkTimeouts() throws Exception { int minTimeout = Math.min(sessionTimeoutMs, connectionTimeoutMs); long elapsed = System.currentTimeMillis() - connectionStartMs; if (elapsed >= minTimeout) { if (zooKeeper.hasNewConnectionString()) { handleNewConnectionString(); } else { int maxTimeout = Math.max(sessionTimeoutMs, connectionTimeoutMs); if (elapsed > maxTimeout) { if (!Boolean.getBoolean(DebugUtils.PROPERTY_DONT_LOG_CONNECTION_ISSUES)) { log.warn(String.format( "Connection attempt unsuccessful after %d (greater than max timeout of %d). Resetting connection and trying again with a new connection.", elapsed, maxTimeout)); } reset(); } else { KeeperException.ConnectionLossException connectionLossException = new CuratorConnectionLossException(); if (!Boolean.getBoolean(DebugUtils.PROPERTY_DONT_LOG_CONNECTION_ISSUES)) { log.error(String.format( "Connection timed out for connection string (%s) and timeout (%d) / elapsed (%d)", zooKeeper.getConnectionString(), connectionTimeoutMs, elapsed), connectionLossException); } new EventTrace("connections-timed-out", tracer.get(), getSessionId()).commit(); throw connectionLossException; } } } } /** * Return the current session id */ public long getSessionId() { long sessionId = 0; try { ZooKeeper zk = zooKeeper.getZooKeeper(); if (zk != null) { sessionId = zk.getSessionId(); } } catch (Exception e) { // Ignore the exception } return sessionId; } private synchronized void reset() throws Exception { log.debug("reset"); instanceIndex.incrementAndGet(); isConnected.set(false); connectionStartMs = System.currentTimeMillis(); zooKeeper.closeAndReset(); zooKeeper.getZooKeeper(); // initiate connection } private boolean checkState(Event.KeeperState state, boolean wasConnected) { boolean isConnected = wasConnected; switch (state) { default: case Disconnected: case Expired: { isConnected = false; break; } case SyncConnected: case ConnectedReadOnly: { isConnected = true; break; } case AuthFailed: { isConnected = false; log.error("Authentication failed"); break; } case SaslAuthenticated: { // NOP break; } } // the session expired is logged in handleExpiredSession, so not log here if (state != Event.KeeperState.Expired) { new EventTrace(state.toString(), tracer.get(), getSessionId()).commit(); } return isConnected; } private void handleState(Event.KeeperState state) { if (state == Event.KeeperState.Expired) { handleExpiredSession(); } else if (zooKeeper.hasNewConnectionString()) { handleNewConnectionString(); } } private void handleNewConnectionString() { log.info("Connection string changed"); new EventTrace("connection-string-changed", tracer.get(), getSessionId()).commit(); try { reset(); } catch (Exception e) { ThreadUtils.checkInterrupted(e); queueBackgroundException(e); } } private void handleExpiredSession() { log.warn("Session expired event received"); new EventTrace("session-expired", tracer.get(), getSessionId()).commit(); try { reset(); } catch (Exception e) { ThreadUtils.checkInterrupted(e); queueBackgroundException(e); } } @SuppressWarnings({ "ThrowableResultOfMethodCallIgnored" }) private void queueBackgroundException(Exception e) { while (backgroundExceptions.size() >= MAX_BACKGROUND_EXCEPTIONS) { backgroundExceptions.poll(); } backgroundExceptions.offer(e); } }