/**
    * 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.coprocessor.example;
  
  import java.io.IOException;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.CoprocessorEnvironment;
  import org.apache.hadoop.hbase.HRegionInfo;
  import org.apache.hadoop.hbase.HTableDescriptor;
  import org.apache.hadoop.hbase.TableName;
  import org.apache.hadoop.hbase.coprocessor.BaseMasterObserver;
  import org.apache.hadoop.hbase.coprocessor.MasterCoprocessorEnvironment;
  import org.apache.hadoop.hbase.coprocessor.ObserverContext;
  import org.apache.hadoop.hbase.metrics.Counter;
  import org.apache.hadoop.hbase.metrics.Gauge;
  import org.apache.hadoop.hbase.metrics.MetricRegistry;
  import org.apache.hadoop.hbase.metrics.Timer;
  
  /**
   * An example coprocessor that collects some metrics to demonstrate the usage of exporting custom
   * metrics from the coprocessor.
   *
   * <p>
   * These metrics will be available through the regular Hadoop metrics2 sinks (ganglia, opentsdb,
   * etc) as well as JMX output. You can view a snapshot of the metrics by going to the http web UI
   * of the master page, something like http://mymasterhost:16010/jmx
   * </p>
   * @see ExampleRegionObserverWithMetrics
   */
  public class ExampleMasterObserverWithMetrics extends BaseMasterObserver {
  
    private static final Log LOG = LogFactory.getLog(ExampleMasterObserverWithMetrics.class);
  
    /** This is the Timer metric object to keep track of the current count across invocations */
    private Timer createTableTimer;
    private long createTableStartTime = Long.MIN_VALUE;
  
    /** This is a Counter object to keep track of disableTable operations */
    private Counter disableTableCounter;
  
    /** Returns the total memory of the process. We will use this to define a gauge metric */
    private long getTotalMemory() {
      return Runtime.getRuntime().totalMemory();
    }
  
    /** Returns the max memory of the process. We will use this to define a gauge metric */
    private long getMaxMemory() {
      return Runtime.getRuntime().maxMemory();
    }
  
    @Override
    public void preCreateTable(ObserverContext<MasterCoprocessorEnvironment> ctx,
                               HTableDescriptor desc, HRegionInfo[] regions) throws IOException {
      super.preCreateTable(ctx, desc, regions);
      // we rely on the fact that there is only 1 instance of our MasterObserver. We keep track of
      // when the operation starts before the operation is executing.
      this.createTableStartTime = System.currentTimeMillis();
    }
  
    @Override
    public void postCreateTable(ObserverContext<MasterCoprocessorEnvironment> ctx,
                                HTableDescriptor desc, HRegionInfo[] regions) throws IOException {
      super.postCreateTable(ctx, desc, regions);
      if (this.createTableStartTime > 0) {
        long time = System.currentTimeMillis() - this.createTableStartTime;
        LOG.info("Create table took: " + time);
  
        // Update the timer metric for the create table operation duration.
        createTableTimer.updateMillis(time);
      }
    }
  
    @Override
    public void preDisableTable(ObserverContext<MasterCoprocessorEnvironment> ctx, TableName tableName) throws IOException {
      super.preDisableTable(ctx, tableName);
  
      // Increment the Counter for disable table operations
      this.disableTableCounter.increment();
    }
  
    @Override
   public void start(CoprocessorEnvironment env) throws IOException {
     super.start(env);
 
     // start for the MasterObserver will be called only once in the lifetime of the
     // server. We will construct and register all metrics that we will track across method
     // invocations.
 
     if (env instanceof MasterCoprocessorEnvironment) {
       // Obtain the MetricRegistry for the Master. Metrics from this registry will be reported
       // at the master level per-server.
       MetricRegistry registry =
           ((MasterCoprocessorEnvironment) env).getMetricRegistryForMaster();
 
       if (createTableTimer == null) {
         // Create a new Counter, or get the already registered counter.
         // It is much better to only call this once and save the Counter as a class field instead
         // of creating the counter every time a coprocessor method is invoked. This will negate
         // any performance bottleneck coming from map lookups tracking metrics in the registry.
         createTableTimer = registry.timer("CreateTable");
 
         // on stop(), we can remove these registered metrics via calling registry.remove(). But
         // it is not needed for coprocessors at the master level. If coprocessor is stopped,
         // the server is stopping anyway, so there will not be any resource leaks.
       }
 
       if (disableTableCounter == null) {
         disableTableCounter = registry.counter("DisableTable");
       }
 
       // Register a custom gauge. The Gauge object will be registered in the metrics registry and
       // periodically the getValue() is invoked to obtain the snapshot.
       registry.register("totalMemory", new Gauge<Long>() {
         @Override
         public Long getValue() {
           return getTotalMemory();
         }
       });
 
       // Register a custom gauge (Supplier converted into Gauge)
       registry.register("maxMemory", new Gauge<Long>() {
         @Override
         public Long getValue() {
           return getMaxMemory();
         }
 
       });
     }
   }
 }