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.master.block.meta;
  
  import com.google.common.collect.Lists;
  
  import java.util.Arrays;
  import java.util.EnumSet;
  import java.util.List;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.locks.Condition;
  import java.util.concurrent.locks.Lock;
  
  /**
   * This class manages the logic of locking multiple sections in {@link MasterWorkerInfo} properly.
   *
   * As mentioned in javadoc of {@link MasterWorkerInfo}, there are multiple groups of metadata
   * that requires external locking. This class is used to provide a clean interface to manage
   * the locking logic and lock life cycles.
   *
   * When multiple {@link WorkerMetaLockSection} are specified, internally the locks will be
   * locked in order, and unlocked in the opposite order, so that deadlock is prevented.
   *
   * This class implements {@link Lock} so it can be managed by
   * {@link alluxio.resource.LockResource}. Callers do not need to lock and unlock explicitly.
   */
  // TODO(jiacheng): Make LockResource support multiple locks so we don't need this wrapper anymore
  public class WorkerMetaLock implements Lock {
    // The order for acquiring locks
    private static final List<WorkerMetaLockSection> NATURAL_ORDER =
        Arrays.asList(WorkerMetaLockSection.values());
    // The order for releasing locks
    private static final List<WorkerMetaLockSection> REVERSE_ORDER = Lists.reverse(NATURAL_ORDER);
  
    private final EnumSet<WorkerMetaLockSection> mLockTypes;
    private final boolean mIsShared;
    private final MasterWorkerInfo mWorker;
  
    /**
     * Constructor.
     *
     * @param lockTypes each {@link WorkerMetaLockSection} corresponds to one section of metadata
     * @param isShared if false, the lock is exclusive
     * @param worker the {@link MasterWorkerInfo} to lock
     */
    WorkerMetaLock(EnumSet<WorkerMetaLockSection> lockTypes, boolean isShared,
         MasterWorkerInfo worker) {
      mLockTypes = lockTypes;
      mIsShared = isShared;
      mWorker = worker;
    }
  
    @Override
    public void lock() {
      for (WorkerMetaLockSection t : NATURAL_ORDER) {
        if (mLockTypes.contains(t)) {
          if (mIsShared) {
            mWorker.getLock(t).readLock().lock();
          } else {
            mWorker.getLock(t).writeLock().lock();
          }
        }
      }
    }
  
    @Override
    public void unlock() {
      for (WorkerMetaLockSection t : REVERSE_ORDER) {
        if (mLockTypes.contains(t)) {
          if (mIsShared) {
            mWorker.getLock(t).readLock().unlock();
          } else {
            mWorker.getLock(t).writeLock().unlock();
          }
        }
      }
    }
  
    @Override
    public void lockInterruptibly() {
      throw new UnsupportedOperationException("lockInterruptibly is not supported!");
    }
  
    @Override
    public boolean tryLock() {
      throw new UnsupportedOperationException("tryLock is not supported!");
    }
  
    @Override
    public boolean tryLock(long time, TimeUnit unit) {
      throw new UnsupportedOperationException("tryLock is not supported!");
    }
  
    @Override
    public Condition newCondition() {
      throw new UnsupportedOperationException("newCondition is not supported!");
    }
  }
  