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 }