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        @Override
040        public void doStart() throws Exception {
041            stopping = false;
042    
043            LOG.info("Attempting to acquire the exclusive lock to become the Master broker");
044            PreparedStatement statement = null;
045            while (true) {
046                try {
047                    connection = dataSource.getConnection();
048                    connection.setAutoCommit(false);
049                    String sql = statements.getLockCreateStatement();
050                    statement = connection.prepareStatement(sql);
051                    if (statement.getMetaData() != null) {
052                        ResultSet rs = statement.executeQuery();
053                        // if not already locked the statement below blocks until lock acquired
054                        rs.next();
055                    } else {
056                        statement.execute();
057                    }
058                    break;
059                } catch (Exception e) {
060                    if (stopping) {
061                        throw new Exception("Cannot start broker as being asked to shut down. Interrupted attempt to acquire lock: " + e, e);
062                    }
063    
064                    if (exceptionHandler != null) {
065                        try {
066                            exceptionHandler.handle(e);
067                        } catch (Throwable handlerException) {
068                            LOG.error("The exception handler " + exceptionHandler.getClass().getCanonicalName() + " threw this exception: " + handlerException
069                                    + " while trying to handle this excpetion: " + e, handlerException);
070                        }
071    
072                    } else {
073                        LOG.error("Failed to acquire lock: " + e, e);
074                    }
075                } finally {
076    
077                    if (null != statement) {
078                        try {
079                            statement.close();
080                        } catch (SQLException e1) {
081                            LOG.warn("Caught while closing statement: " + e1, e1);
082                        }
083                        statement = null;
084                    }
085                }
086    
087                LOG.debug("Sleeping for " + lockAcquireSleepInterval + " milli(s) before trying again to get the lock...");
088                try {
089                    Thread.sleep(lockAcquireSleepInterval);
090                } catch (InterruptedException ie) {
091                    LOG.warn("Master lock retry sleep interrupted", ie);
092                }
093            }
094    
095            LOG.info("Becoming the master on dataSource: " + dataSource);
096        }
097    
098    }