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Lucene example source code file (Lock.java)

This example Lucene source code file (Lock.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

interruptedexception, io, ioexception, ioexception, lock, lock, lock_obtain_wait_forever, lock_obtain_wait_forever, lock_poll_interval, lockobtainfailedexception, lockobtainfailedexception, object, string, threadinterruptedexception, with

The Lucene Lock.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 org.apache.lucene.util.ThreadInterruptedException;
import java.io.IOException;

/** An interprocess mutex lock.
 * <p>Typical use might look like:
 * new Lock.With(directory.makeLock("my.lock")) {
 *     public Object doBody() {
 *       <i>... code to execute while locked ...
 *     }
 *   }.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 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();
      }
    }
  }

}

Other Lucene examples (source code examples)

Here is a short list of links related to this Lucene Lock.java source code file:



my book on functional programming

 

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