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 com.alibaba.metrics.jvm;
  
  import com.alibaba.metrics.CachedGauge;
  import com.alibaba.metrics.RatioGauge;
  import com.sun.management.UnixOperatingSystemMXBean;
  
  import java.lang.management.ManagementFactory;
  import java.lang.management.OperatingSystemMXBean;
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  import java.util.concurrent.TimeUnit;
  
  /**
   * A gauge for the ratio of used to total file descriptors.
   */
  public class FileDescriptorRatioGauge extends RatioGauge {
  
      private final OperatingSystemMXBean os;
  
      private final CachedGauge<Ratio> cachedRatio;
  
      /**
       * Creates a new gauge using the platform OS bean.
       */
      public FileDescriptorRatioGauge() {
          this(ManagementFactory.getOperatingSystemMXBean(), 1, TimeUnit.MINUTES);
      }
  
      public FileDescriptorRatioGauge(OperatingSystemMXBean os) {
          this(os, 1, TimeUnit.MINUTES);
      }
  
      /**
       * Creates a new gauge using the given OS bean.
       *
       * @param os    an {@link OperatingSystemMXBean}
       */
      public FileDescriptorRatioGauge(OperatingSystemMXBean os, long timeout, TimeUnit unit) {
          this.os = os;
          cachedRatio = new CachedGauge<Ratio>(timeout, unit) {
              @Override
              protected Ratio loadValue() {
                  return getRatioInternal();
              }
          };
      }
  
      @Override
      protected Ratio getRatio() {
          return cachedRatio.getValue();
      }
  
      private Ratio getRatioInternal() {
          if (os instanceof UnixOperatingSystemMXBean) {
              final UnixOperatingSystemMXBean unixOs = (UnixOperatingSystemMXBean) os;
              return Ratio.of(unixOs.getOpenFileDescriptorCount(), unixOs.getMaxFileDescriptorCount());
          } else {
              return Ratio.of(Double.NaN, Double.NaN);
          }
  //        try {
  //            return Ratio.of(invoke("getOpenFileDescriptorCount"),
  //                    invoke("getMaxFileDescriptorCount"));
  //        } catch (NoSuchMethodException e) {
  //            return Ratio.of(Double.NaN, Double.NaN);
  //        } catch (IllegalAccessException e) {
  //            return Ratio.of(Double.NaN, Double.NaN);
  //        } catch (InvocationTargetException e) {
  //            return Ratio.of(Double.NaN, Double.NaN);
  //        }
      }
  
      private long invoke(String name) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
          final Method method = os.getClass().getDeclaredMethod(name);
          method.setAccessible(true);
          return (Long) method.invoke(os);
      }
  }
  