001 /**
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017 package org.apache.activemq.store.jdbc.adapter;
018
019 import java.io.IOException;
020 import java.sql.PreparedStatement;
021 import java.sql.ResultSet;
022 import java.sql.SQLException;
023
024 import org.apache.activemq.store.jdbc.DefaultDatabaseLocker;
025 import org.apache.activemq.store.jdbc.JDBCPersistenceAdapter;
026 import org.slf4j.Logger;
027 import org.slf4j.LoggerFactory;
028
029 /**
030 * Represents an exclusive lock on a database to avoid multiple brokers running
031 * against the same logical database.
032 *
033 * @org.apache.xbean.XBean element="transact-database-locker"
034 *
035 */
036 public class TransactDatabaseLocker extends DefaultDatabaseLocker {
037 private static final Logger LOG = LoggerFactory.getLogger(TransactDatabaseLocker.class);
038
039 public TransactDatabaseLocker() {
040 }
041
042 public TransactDatabaseLocker(JDBCPersistenceAdapter persistenceAdapter) throws IOException {
043 setPersistenceAdapter(persistenceAdapter);
044 }
045
046 @Override
047 public void start() throws Exception {
048 stopping = false;
049
050 LOG.info("Attempting to acquire the exclusive lock to become the Master broker");
051 PreparedStatement statement = null;
052 while (true) {
053 try {
054 connection = dataSource.getConnection();
055 connection.setAutoCommit(false);
056 String sql = statements.getLockCreateStatement();
057 statement = connection.prepareStatement(sql);
058 if (statement.getMetaData() != null) {
059 ResultSet rs = statement.executeQuery();
060 // if not already locked the statement below blocks until lock acquired
061 rs.next();
062 } else {
063 statement.execute();
064 }
065 break;
066 } catch (Exception e) {
067 if (stopping) {
068 throw new Exception("Cannot start broker as being asked to shut down. Interrupted attempt to acquire lock: " + e, e);
069 }
070
071 if (exceptionHandler != null) {
072 try {
073 exceptionHandler.handle(e);
074 } catch (Throwable handlerException) {
075 LOG.error("The exception handler " + exceptionHandler.getClass().getCanonicalName() + " threw this exception: " + handlerException
076 + " while trying to handle this excpetion: " + e, handlerException);
077 }
078
079 } else {
080 LOG.error("Failed to acquire lock: " + e, e);
081 }
082 } finally {
083
084 if (null != statement) {
085 try {
086 statement.close();
087 } catch (SQLException e1) {
088 LOG.warn("Caught while closing statement: " + e1, e1);
089 }
090 statement = null;
091 }
092 }
093
094 LOG.debug("Sleeping for " + lockAcquireSleepInterval + " milli(s) before trying again to get the lock...");
095 try {
096 Thread.sleep(lockAcquireSleepInterval);
097 } catch (InterruptedException ie) {
098 LOG.warn("Master lock retry sleep interrupted", ie);
099 }
100 }
101
102 LOG.info("Becoming the master on dataSource: " + dataSource);
103 }
104
105 }