content: /*
   * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
   * (the "License"). You may not use this work except in compliance with the License, which is
   * available at www.apache.org/licenses/LICENSE-2.0
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied, as more fully set forth in the License.
   *
   * See the NOTICE file distributed with this work for information regarding copyright ownership.
   */
  
  package alluxio.resource;
  
  import com.google.common.annotations.VisibleForTesting;
  import io.netty.util.ResourceLeakDetector;
  import io.netty.util.ResourceLeakTracker;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.io.Closeable;
  import java.util.concurrent.locks.Lock;
  import java.util.concurrent.locks.LockSupport;
  import javax.annotation.Nullable;
  
  /**
   * A resource lock that makes it possible to acquire and release locks using the following idiom:
   *
   * <pre>
   *   try (LockResource r = new LockResource(lock)) {
   *     ...
   *   }
   * </pre>
   *
   * The subclasses will be tracked by the leak detector.
   * The subclasses should call super.close() in their close(), otherwise a leak will be reported.
   */
  // extends Closeable instead of AutoCloseable to enable usage with Guava's Closer.
  public class LockResource implements Closeable {
    private static final Logger LOG = LoggerFactory.getLogger(LockResource.class);
  
    private static final ResourceLeakDetector<LockResource> DETECTOR =
        AlluxioResourceLeakDetectorFactory.instance().newResourceLeakDetector(LockResource.class);
  
    // The lock which represents the resource. It should only be written or modified by subclasses
    // attempting to downgrade locks (see RWLockResource).
    protected Lock mLock;
    private final Runnable mCloseAction;
    @Nullable
    private ResourceLeakTracker<LockResource> mTracker = DETECTOR.track(this);
  
    /**
     * Creates a new instance of {@link LockResource} using the given lock.
     *
     * @param lock the lock to acquire
     */
    public LockResource(Lock lock) {
      this(lock, true, false);
    }
  
    /**
     * Creates a new instance of {@link LockResource} using the given lock.
     *
     * This method may use the {@link Lock#tryLock()} method to gain ownership of the locks. The
     * reason one might want to use this is to avoid the fairness heuristics within the
     * {@link java.util.concurrent.locks.ReentrantReadWriteLock}'s NonFairSync which may block reader
     * threads if a writer is the first in the queue.
     *
     * @param lock the lock to acquire
     * @param acquireLock whether to lock the lock
     * @param useTryLock whether or not use to {@link Lock#tryLock()}
     */
    public LockResource(Lock lock, boolean acquireLock, boolean useTryLock) {
      this(lock, acquireLock, useTryLock, null);
    }
  
    /**
     * Creates a new instance of {@link LockResource} using the given lock.
     *
     * This method may use the {@link Lock#tryLock()} method to gain ownership of the locks. The
     * reason one might want to use this is to avoid the fairness heuristics within the
     * {@link java.util.concurrent.locks.ReentrantReadWriteLock}'s NonFairSync which may block reader
     * threads if a writer is the first in the queue.
     *
     * @param lock the lock to acquire
     * @param acquireLock whether to lock the lock
     * @param useTryLock whether or not use to {@link Lock#tryLock()}
     * @param closeAction the nullable closeable that will be run before releasing the lock
     */
    public LockResource(Lock lock, boolean acquireLock, boolean useTryLock,
        @Nullable Runnable closeAction) {
      mLock = lock;
      mCloseAction = closeAction;
      if (acquireLock) {
        if (useTryLock) {
          while (!mLock.tryLock()) { // returns immediately
            // The reason we don't use #tryLock(int, TimeUnit) here is because we found there is a bug
            // somewhere in the internal accounting of the ReentrantRWLock that, even though all
            // threads had released the lock, that a final thread would never be able to acquire it.
            LockSupport.parkNanos(10000);
          }
        } else {
          mLock.lock();
        }
      }
    }
  
    /**
     * Returns true if the other {@link LockResource} contains the same lock.
     *
     * @param other other LockResource
     * @return true if the other lockResource has the same lock
     */
    @VisibleForTesting
    public boolean hasSameLock(LockResource other) {
      return mLock == other.mLock;
    }
  
    /**
     * Releases the lock.
     */
    @Override
    public void close() {
      if (mCloseAction != null) {
        mCloseAction.run();
      }
      if (mTracker != null) {
        mTracker.close(this);
      }
      mLock.unlock();
    }
  }
  