content: 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<String>();
  
    @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;
    }
  }
  