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 java.lang.management.ManagementFactory;
  import java.lang.management.OperatingSystemMXBean;
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  import java.util.concurrent.TimeUnit;
  
  import com.alibaba.metrics.CachedGauge;
  
  /**
  * @author boshu
  * @version create time：2019年1月18日 上午11:38:35
  *
  */
  public class FileDescriptorGauge extends CachedGauge<Long>{
  
      private final OperatingSystemMXBean os;
  
      public FileDescriptorGauge(long timeout, TimeUnit timeoutUnit) {
          super(timeout, timeoutUnit);
          os = ManagementFactory.getOperatingSystemMXBean();
      }
  
      public FileDescriptorGauge(long timeout, TimeUnit timeoutUnit, OperatingSystemMXBean os) {
          super(timeout, timeoutUnit);
          this.os = os;
      }
  
      @Override
      protected Long loadValue() {
          try {
              return invoke("getOpenFileDescriptorCount");
          } catch (Throwable e) {
              return 0L;
          }
      }
  
      private long invoke(String name) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
          final Method method = os.getClass().getDeclaredMethod(name);
          method.setAccessible(true);
          return (Long) method.invoke(os);
      }
  }
  