Lucene example source code file (SingleInstanceLockFactory.java)

This example Lucene source code file (SingleInstanceLockFactory.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Lucene tags/keywords

hashset, hashset, io, ioexception, lock, lockfactory, override, override, singleinstancelock, singleinstancelock, singleinstancelockfactory, string, string, util

The Lucene SingleInstanceLockFactory.java source code

package org.apache.lucene.store;

/**
 * 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.
 */

import java.io.IOException;
import java.util.HashSet;

/**
 * Implements {@link LockFactory} for a single in-process instance,
 * meaning all locking will take place through this one instance.
 * Only use this {@link LockFactory} when you are certain all
 * IndexReaders and IndexWriters for a given index are running
 * against a single shared in-process Directory instance.  This is
 * currently the default locking for RAMDirectory.
 *
 * @see LockFactory
 */

public class SingleInstanceLockFactory extends LockFactory {

  private HashSet<String> locks = new HashSet();

  @Override
  public Lock makeLock(String lockName) {
    // We do not use the LockPrefix at all, because the private
    // HashSet instance effectively scopes the locking to this
    // single Directory instance.
    return new SingleInstanceLock(locks, lockName);
  }

  @Override
  public void clearLock(String lockName) throws IOException {
    synchronized(locks) {
      if (locks.contains(lockName)) {
        locks.remove(lockName);
      }
    }
  }
}

class SingleInstanceLock extends Lock {

  String lockName;
  private HashSet<String> locks;

  public SingleInstanceLock(HashSet<String> locks, String lockName) {
    this.locks = locks;
    this.lockName = lockName;
  }

  @Override
  public boolean obtain() throws IOException {
    synchronized(locks) {
      return locks.add(lockName);
    }
  }

  @Override
  public void release() {
    synchronized(locks) {
      locks.remove(lockName);
    }
  }

  @Override
  public boolean isLocked() {
    synchronized(locks) {
      return locks.contains(lockName);
    }
  }

  @Override
  public String toString() {
    return super.toString() + ": " + lockName;
  }
}