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;
018    
019    import java.io.IOException;
020    import java.sql.Connection;
021    import java.sql.PreparedStatement;
022    import java.sql.SQLException;
023    
024    import javax.sql.DataSource;
025    
026    import org.apache.activemq.util.Handler;
027    import org.slf4j.Logger;
028    import org.slf4j.LoggerFactory;
029    
030    /**
031     * Represents an exclusive lock on a database to avoid multiple brokers running
032     * against the same logical database.
033     * 
034     * @org.apache.xbean.XBean element="database-locker"
035     * 
036     */
037    public class DefaultDatabaseLocker implements DatabaseLocker {
038        public static final long DEFAULT_LOCK_ACQUIRE_SLEEP_INTERVAL = 1000;
039        private static final Logger LOG = LoggerFactory.getLogger(DefaultDatabaseLocker.class);
040        protected DataSource dataSource;
041        protected Statements statements;
042        protected long lockAcquireSleepInterval = DEFAULT_LOCK_ACQUIRE_SLEEP_INTERVAL;
043    
044        protected Connection connection;
045        protected boolean stopping;
046        protected Handler<Exception> exceptionHandler;
047        
048        public DefaultDatabaseLocker() {
049        }
050        
051        public DefaultDatabaseLocker(JDBCPersistenceAdapter persistenceAdapter) throws IOException {
052            setPersistenceAdapter(persistenceAdapter);
053        }
054    
055        public void setPersistenceAdapter(JDBCPersistenceAdapter adapter) throws IOException {
056            this.dataSource = adapter.getLockDataSource();
057            this.statements = adapter.getStatements();
058        }
059        
060        public void start() throws Exception {
061            stopping = false;
062    
063            LOG.info("Attempting to acquire the exclusive lock to become the Master broker");
064            String sql = statements.getLockCreateStatement();
065            LOG.debug("Locking Query is "+sql);
066            
067            PreparedStatement statement = null;
068            while (true) {
069                try {
070                    connection = dataSource.getConnection();
071                    connection.setAutoCommit(false);
072                    statement = connection.prepareStatement(sql);
073                    statement.execute();
074                    break;
075                } catch (Exception e) {
076                    try {
077                        if (stopping) {
078                            throw new Exception(
079                                    "Cannot start broker as being asked to shut down. " 
080                                            + "Interrupted attempt to acquire lock: "
081                                            + e, e);
082                        }
083                        if (exceptionHandler != null) {
084                            try {
085                                exceptionHandler.handle(e);
086                            } catch (Throwable handlerException) {
087                                LOG.error( "The exception handler "
088                                        + exceptionHandler.getClass().getCanonicalName()
089                                        + " threw this exception: "
090                                        + handlerException
091                                        + " while trying to handle this exception: "
092                                        + e, handlerException);
093                            }
094    
095                        } else {
096                            LOG.debug("Lock failure: "+ e, e);
097                        }
098                    } finally {
099                        // Let's make sure the database connection is properly
100                        // closed when an error occurs so that we're not leaking
101                        // connections 
102                        if (null != connection) {
103                            try {
104                                connection.close();
105                            } catch (SQLException e1) {
106                                LOG.error("Caught exception while closing connection: " + e1, e1);
107                            }
108                            
109                            connection = null;
110                        }
111                    }
112                } finally {
113                    if (null != statement) {
114                        try {
115                            statement.close();
116                        } catch (SQLException e1) {
117                            LOG.debug("Caught while closing statement: " + e1, e1);
118                        }
119                        statement = null;
120                    }
121                }
122    
123                LOG.info("Failed to acquire lock.  Sleeping for " + lockAcquireSleepInterval + " milli(s) before trying again...");
124                try {
125                    Thread.sleep(lockAcquireSleepInterval);
126                } catch (InterruptedException ie) {
127                    LOG.warn("Master lock retry sleep interrupted", ie);
128                }
129            }
130    
131            LOG.info("Becoming the master on dataSource: " + dataSource);
132        }
133    
134        public void stop() throws Exception {
135            stopping = true;
136            try {
137                if (connection != null && !connection.isClosed()) {
138                    try {
139                        connection.rollback();
140                    } catch (SQLException sqle) {
141                        LOG.warn("Exception while rollbacking the connection on shutdown", sqle);
142                    } finally {
143                        try {
144                            connection.close();
145                        } catch (SQLException ignored) {
146                            LOG.debug("Exception while closing connection on shutdown", ignored);
147                        }
148                    }
149                }
150            } catch (SQLException sqle) {
151                LOG.warn("Exception while checking close status of connection on shutdown", sqle);
152            }
153        }
154    
155        public boolean keepAlive() {
156            PreparedStatement statement = null;
157            boolean result = false;
158            try {
159                statement = connection.prepareStatement(statements.getLockUpdateStatement());
160                statement.setLong(1, System.currentTimeMillis());
161                int rows = statement.executeUpdate();
162                if (rows == 1) {
163                    result=true;
164                }
165            } catch (Exception e) {
166                LOG.error("Failed to update database lock: " + e, e);
167            } finally {
168                if (statement != null) {
169                    try {
170                        statement.close();
171                    } catch (SQLException e) {
172                        LOG.error("Failed to close statement",e);
173                    }
174                }
175            }
176            return result;
177        }
178     
179        public long getLockAcquireSleepInterval() {
180            return lockAcquireSleepInterval;
181        }
182    
183        public void setLockAcquireSleepInterval(long lockAcquireSleepInterval) {
184            this.lockAcquireSleepInterval = lockAcquireSleepInterval;
185        }
186        
187        public Handler getExceptionHandler() {
188            return exceptionHandler;
189        }
190    
191        public void setExceptionHandler(Handler exceptionHandler) {
192            this.exceptionHandler = exceptionHandler;
193        }
194    
195    }