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.apache.commons.logging.Log;
027    import org.apache.commons.logging.LogFactory;
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     * @version $Revision: 818910 $
035     */
036    public class TransactDatabaseLocker extends DefaultDatabaseLocker {
037        private static final Log LOG = LogFactory.getLog(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    }