/**
    * 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.Collections;
  import java.util.Set;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.TimeUnit;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.metrics.BaseSourceImpl;
  import org.apache.hadoop.hbase.metrics.Interns;
  import org.apache.hadoop.metrics2.MetricsCollector;
  import org.apache.hadoop.metrics2.MetricsRecordBuilder;
  import org.apache.hadoop.metrics2.impl.JmxCacheBuster;
  import org.apache.hadoop.metrics2.lib.MetricsExecutorImpl;
  
  @InterfaceAudience.Private
  public class MetricsRegionAggregateSourceImpl extends BaseSourceImpl
      implements MetricsRegionAggregateSource {
  
    private static final Log LOG = LogFactory.getLog(MetricsRegionAggregateSourceImpl.class);
  
    private final MetricsExecutorImpl executor = new MetricsExecutorImpl();
  
    private final Set<MetricsRegionSource> regionSources =
        Collections.newSetFromMap(new ConcurrentHashMap<MetricsRegionSource, Boolean>());
  
    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);
  
      // Every few mins clean the JMX cache.
      executor.getExecutor().scheduleWithFixedDelay(new Runnable() {
        public void run() {
          JmxCacheBuster.clearJmxCache();
        }
      }, 5, 5, TimeUnit.MINUTES);
    }
  
    @Override
    public void register(MetricsRegionSource source) {
      regionSources.add(source);
      clearCache();
    }
  
    @Override
    public void deregister(MetricsRegionSource toRemove) {
      try {
        regionSources.remove(toRemove);
      } catch (Exception e) {
        // Ignored. If this errors out it means that someone is double
        // closing the region source and the region is already nulled out.
        LOG.info(
            "Error trying to remove " + toRemove + " from " + this.getClass().getSimpleName(),
            e);
      }
      clearCache();
    }
  
    private synchronized void clearCache() {
      JmxCacheBuster.clearJmxCache();
    }
  
    /**
     * 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) {
       for (MetricsRegionSource regionMetricSource : regionSources) {
         if (regionMetricSource instanceof MetricsRegionSourceImpl) {
           ((MetricsRegionSourceImpl) regionMetricSource).snapshot(mrb, all);
         }
       }
       mrb.addGauge(Interns.info(NUM_REGIONS, NUMBER_OF_REGIONS_DESC), regionSources.size());
       metricsRegistry.snapshot(mrb, all);
     }
   }
 }