/**
    * 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.hadoop.hbase.regionserver;
  
  import java.util.TreeSet;
  import java.util.concurrent.locks.ReentrantReadWriteLock;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.metrics.BaseSourceImpl;
  import org.apache.hadoop.metrics2.MetricsCollector;
  import org.apache.hadoop.metrics2.MetricsRecordBuilder;
  
  @InterfaceAudience.Private
  public class MetricsRegionAggregateSourceImpl extends BaseSourceImpl
      implements MetricsRegionAggregateSource {
  
    // lock to guard against concurrent access to regionSources
    private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
  
    private final TreeSet<MetricsRegionSourceImpl> regionSources =
        new TreeSet<MetricsRegionSourceImpl>();
  
    public MetricsRegionAggregateSourceImpl() {
      this(METRICS_NAME, METRICS_DESCRIPTION, METRICS_CONTEXT, METRICS_JMX_CONTEXT);
    }
  
  
    public MetricsRegionAggregateSourceImpl(String metricsName,
                                            String metricsDescription,
                                            String metricsContext,
                                            String metricsJmxContext) {
      super(metricsName, metricsDescription, metricsContext, metricsJmxContext);
    }
  
    @Override
    public void register(MetricsRegionSource source) {
      lock.writeLock().lock();
      try {
        regionSources.add((MetricsRegionSourceImpl) source);
      } finally {
        lock.writeLock().unlock();
      }
    }
  
    @Override
    public void deregister(MetricsRegionSource source) {
      lock.writeLock().lock();
      try {
        regionSources.remove(source);
      } finally {
        lock.writeLock().unlock();
      }
    }
  
    /**
     * Yes this is a get function that doesn't return anything.  Thanks Hadoop for breaking all
     * expectations of java programmers.  Instead of returning anything Hadoop metrics expects
     * getMetrics to push the metrics into the collector.
     *
     * @param collector the collector
     * @param all       get all the metrics regardless of when they last changed.
     */
    @Override
    public void getMetrics(MetricsCollector collector, boolean all) {
  
  
      MetricsRecordBuilder mrb = collector.addRecord(metricsName);
  
      if (regionSources != null) {
        lock.readLock().lock();
        try {
          for (MetricsRegionSourceImpl regionMetricSource : regionSources) {
            regionMetricSource.snapshot(mrb, all);
          }
        } finally {
          lock.readLock().unlock();
        }
      }
  
      metricsRegistry.snapshot(mrb, all);
    }
  }