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 org.apache.lucene.util.ThreadInterruptedException;
  import java.io.IOException;
  
  /** An interprocess mutex lock.
   * <p>Typical use might look like:<pre>
   * new Lock.With(directory.makeLock("my.lock")) {
   *     public Object doBody() {
   *       <i>... code to execute while locked ...</i>
   *     }
   *   }.run();
   * </pre>
   *
   * @see Directory#makeLock(String)
   */
  public abstract class Lock {
  
    /** How long {@link #obtain(long)} waits, in milliseconds,
     *  in between attempts to acquire the lock. */
    public static long LOCK_POLL_INTERVAL = 1000;
  
    /** Pass this value to {@link #obtain(long)} to try
     *  forever to obtain the lock. */
    public static final long LOCK_OBTAIN_WAIT_FOREVER = -1;
  
    /** Attempts to obtain exclusive access and immediately return
     *  upon success or failure.
     * @return true iff exclusive access is obtained
     */
    public abstract boolean obtain() throws IOException;
  
    /**
     * If a lock obtain called, this failureReason may be set
     * with the "root cause" Exception as to why the lock was
     * not obtained.
     */
    protected Throwable failureReason;
  
    /** Attempts to obtain an exclusive lock within amount of
     *  time given. Polls once per {@link #LOCK_POLL_INTERVAL}
     *  (currently 1000) milliseconds until lockWaitTimeout is
     *  passed.
     * @param lockWaitTimeout length of time to wait in
     *        milliseconds or {@link
     *        #LOCK_OBTAIN_WAIT_FOREVER} to retry forever
     * @return true if lock was obtained
     * @throws LockObtainFailedException if lock wait times out
     * @throws IllegalArgumentException if lockWaitTimeout is
     *         out of bounds
     * @throws IOException if obtain() throws IOException
     */
    public boolean obtain(long lockWaitTimeout) throws LockObtainFailedException, IOException {
      failureReason = null;
      boolean locked = obtain();
      if (lockWaitTimeout < 0 && lockWaitTimeout != LOCK_OBTAIN_WAIT_FOREVER)
        throw new IllegalArgumentException("lockWaitTimeout should be LOCK_OBTAIN_WAIT_FOREVER or a non-negative number (got " + lockWaitTimeout + ")");
  
      long maxSleepCount = lockWaitTimeout / LOCK_POLL_INTERVAL;
      long sleepCount = 0;
      while (!locked) {
        if (lockWaitTimeout != LOCK_OBTAIN_WAIT_FOREVER && sleepCount++ >= maxSleepCount) {
          String reason = "Lock obtain timed out: " + this.toString();
          if (failureReason != null) {
            reason += ": " + failureReason;
          }
          LockObtainFailedException e = new LockObtainFailedException(reason);
          if (failureReason != null) {
            e.initCause(failureReason);
          }
          throw e;
        }
        try {
          Thread.sleep(LOCK_POLL_INTERVAL);
        } catch (InterruptedException ie) {
          throw new ThreadInterruptedException(ie);
        }
        locked = obtain();
      }
      return locked;
    }
  
    /** Releases exclusive access. */
    public abstract void release() throws IOException;
  
    /** Returns true if the resource is currently locked.  Note that one must
     * still call {@link #obtain()} before using the resource. */
    public abstract boolean isLocked() throws IOException;
  
  
    /** Utility class for executing code with exclusive access. */
    public abstract static class With {
      private Lock lock;
      private long lockWaitTimeout;
  
  
      /** Constructs an executor that will grab the named lock. */
      public With(Lock lock, long lockWaitTimeout) {
        this.lock = lock;
        this.lockWaitTimeout = lockWaitTimeout;
      }
  
      /** Code to execute with exclusive access. */
      protected abstract Object doBody() throws IOException;
  
      /** Calls {@link #doBody} while <i>lock</i> is obtained.  Blocks if lock
       * cannot be obtained immediately.  Retries to obtain lock once per second
       * until it is obtained, or until it has tried ten times. Lock is released when
       * {@link #doBody} exits.
       * @throws LockObtainFailedException if lock could not
       * be obtained
       * @throws IOException if {@link Lock#obtain} throws IOException
       */
      public Object run() throws LockObtainFailedException, IOException {
        boolean locked = false;
        try {
           locked = lock.obtain(lockWaitTimeout);
           return doBody();
        } finally {
          if (locked)
  	      lock.release();
        }
      }
    }
  
  }
  