content: /**
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License.  You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.activemq.store;
  
  import java.io.File;
  import java.io.IOException;
  import java.util.concurrent.TimeUnit;
  
  import org.apache.activemq.broker.AbstractLocker;
  import org.apache.activemq.util.LockFile;
  import org.apache.activemq.util.ServiceStopper;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Represents an exclusive lock on a database to avoid multiple brokers running
   * against the same logical database.
   *
   * @org.apache.xbean.XBean element="shared-file-locker"
   *
   */
  public class SharedFileLocker extends AbstractLocker {
  
      public static final File DEFAULT_DIRECTORY = new File("KahaDB");
      private static final Logger LOG = LoggerFactory.getLogger(SharedFileLocker.class);
  
      private LockFile lockFile;
      protected File directory = DEFAULT_DIRECTORY;
  
      @Override
      public void doStart() throws Exception {
          if (lockFile == null) {
              File lockFileName = new File(directory, "lock");
              lockFile = new LockFile(lockFileName, false);
              if (failIfLocked) {
                  lockFile.lock();
              } else {
                  // Print a warning only once
                  boolean warned = false;
                  boolean locked = false;
                  while ((!isStopped()) && (!isStopping())) {
                      try {
                          lockFile.lock();
                          if (warned) {
                              // ensure lockHolder has released; wait for one keepAlive iteration
                              try {
                                  TimeUnit.MILLISECONDS.sleep(lockable != null ? lockable.getLockKeepAlivePeriod() : 0l);
                              } catch (InterruptedException e1) {
                              }
                          }
                          locked = keepAlive();
                          break;
                      } catch (IOException e) {
                          if (!warned)
                          {
                              LOG.info("Database "
                                           + lockFileName
                                           + " is locked by another server. This broker is now in slave mode waiting a lock to be acquired");
                              warned = true;
                          }
  
                          LOG.debug("Database "
                                      + lockFileName
                                      + " is locked... waiting "
                                      + (lockAcquireSleepInterval / 1000)
                                      + " seconds for the database to be unlocked. Reason: "
                                      + e);
                          try {
                              TimeUnit.MILLISECONDS.sleep(lockAcquireSleepInterval);
                          } catch (InterruptedException e1) {
                          }
                      }
                  }
                  if (!locked) {
                      throw new IOException("attempt to obtain lock aborted due to shutdown");
                  }
              }
          }
      }
  
      @Override
      public boolean keepAlive() {
          boolean result = lockFile != null && lockFile.keepAlive();
          LOG.trace("keepAlive result: " + result + (name != null ? ", name: " + name : ""));
          return result;
      }
  
      @Override
      public void doStop(ServiceStopper stopper) throws Exception {
          if (lockFile != null) {
              lockFile.unlock();
              lockFile = null;
          }
      }
  
      public File getDirectory() {
          return directory;
      }
  
      public void setDirectory(File directory) {
          this.directory = directory;
      }
  
      @Override
      public void configure(PersistenceAdapter persistenceAdapter) throws IOException {
          this.setDirectory(persistenceAdapter.getDirectory());
          if (name == null) {
              name = getDirectory().toString();
          }
      }
  }
  