content: /*
   * 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.
   */
  package org.apache.ambari.server.orm;
  
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.locks.Condition;
  import java.util.concurrent.locks.Lock;
  import java.util.concurrent.locks.ReadWriteLock;
  import java.util.concurrent.locks.ReentrantReadWriteLock;
  
  import org.apache.ambari.annotations.TransactionalLock.LockArea;
  import org.apache.ambari.server.configuration.Configuration;
  
  import com.google.inject.Inject;
  import com.google.inject.Singleton;
  import com.google.inject.persist.Transactional;
  
  /**
   * The {@link TransactionalLocks} class is used to manage the locks associated
   * with each {@link LockArea}. It's a singlegon that shoudl always be injected.
   */
  @Singleton
  public class TransactionalLocks {
  
    /**
     * Used to lookup whether {@link LockArea}s are enabled.
     */
    private final Configuration m_configuration;
  
    /**
     * Manages the locks for each class which uses the {@link Transactional}
     * annotation.
     */
    private final ConcurrentHashMap<LockArea, ReadWriteLock> m_locks;
  
  
    /**
     * Constructor.
     *
     */
    @Inject
    private TransactionalLocks(Configuration configuration) {
      m_configuration = configuration;
      m_locks = new ConcurrentHashMap<>();
  
      for (LockArea lockArea : LockArea.values()) {
        final ReadWriteLock lock;
        if (lockArea.isEnabled(m_configuration)) {
          lock = new ReentrantReadWriteLock(true);
        } else {
          lock = new NoOperationReadWriteLock();
        }
  
        m_locks.put(lockArea, lock);
      }
    }
  
    /**
     * Gets a lock for the specified lock area. There is a 1:1 relationship
     * between a lock area and a lock.
     * <p/>
     * If the {@link LockArea} is not enabled, then this will return an empty
     * {@link Lock} implementation which doesn't actually lock anything.
     *
     * @param lockArea
     *          the lock area to get the lock for (not {@code null}).
     * @return the lock to use for the specified lock area (never {@code null}).
     */
    public ReadWriteLock getLock(LockArea lockArea) {
      return m_locks.get(lockArea);
    }
  
    /**
     * A dummy implementation of a {@link ReadWriteLock} that returns locks which
     * only NOOP. This is used for cases where dependant code doesn't want to
     * {@code if/else} all over the place.
     */
    private final static class NoOperationReadWriteLock implements ReadWriteLock {
  
      private final Lock m_readLock = new NoOperationLock();
      private final Lock m_writeLock = new NoOperationLock();
  
      /**
       * {@inheritDoc}
       */
      @Override
      public Lock readLock() {
        return m_readLock;
      }
  
      /**
       * {@inheritDoc}
       */
      @Override
      public Lock writeLock() {
        return m_writeLock;
      }
    }
  
    /**
     * A dummy implementation of a {@link Lock} that only NOOPs. This is used for
     * cases where dependant code doesn't want to {@code if/else} all over the
     * place.
     */
    private final static class NoOperationLock implements Lock {
  
      /**
       * NOOP
       * <p/>
       * {@inheritDoc}
       */
      @Override
      public void lock() {
      }
  
      /**
       * NOOP
       * <p/>
       * {@inheritDoc}
       */
      @Override
      public void lockInterruptibly() throws InterruptedException {
      }
  
      /**
       * NOOP, returns {@code true} always.
       * <p/>
       * {@inheritDoc}
       */
      @Override
      public boolean tryLock() {
        return true;
      }
  
      /**
       * NOOP, returns {@code true} always.
       * <p/>
       * {@inheritDoc}
       */
      @Override
      public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
        return true;
      }
  
      /**
       * NOOP
       * <p/>
       * {@inheritDoc}
       */
      @Override
      public void unlock() {
      }
  
      /**
       * NOOP
       * <p/>
       * {@inheritDoc}
       */
      @Override
      public Condition newCondition() {
        return null;
      }
    }
  }
  