/**
    * 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.util;
  
  import java.lang.management.ManagementFactory;
  import java.lang.management.OperatingSystemMXBean;
  import java.lang.management.RuntimeMXBean;
  
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  import java.lang.reflect.Method;
  
  import org.apache.hadoop.classification.InterfaceAudience;
  import org.apache.hadoop.classification.InterfaceStability;
  
  
  /**
   * This class is a wrapper for the implementation of
   * com.sun.management.UnixOperatingSystemMXBean
   * It will decide to use the sun api or its own implementation
   * depending on the runtime (vendor) used.
   */
  
  @InterfaceAudience.Public
  @InterfaceStability.Evolving
  public class JVM 
  {
    static final Logger LOG = LoggerFactory.getLogger(JVM.class);
  
    private OperatingSystemMXBean osMbean;
  
    private static final boolean ibmvendor =
      System.getProperty("java.vendor").contains("IBM");
    private static final boolean windows = 
      System.getProperty("os.name").startsWith("Windows");
    private static final boolean linux =
      System.getProperty("os.name").startsWith("Linux");
    private static final String JVMVersion = System.getProperty("java.version");
  
    /**
     * Constructor. Get the running Operating System instance
     */
    public JVM () {
      this.osMbean = ManagementFactory.getOperatingSystemMXBean();
    }
   
    /**
     * Check if the OS is unix. 
     * 
     * @return whether this is unix or not.
     */
    public static boolean isUnix() {
      if (windows) {
        return false;
      }
      return (ibmvendor ? linux : true);
    }
    
    /**
     * Check if the finish() method of GZIPOutputStream is broken
     * 
     * @return whether GZIPOutputStream.finish() is broken.
     */
    public static boolean isGZIPOutputStreamFinishBroken() {
      return ibmvendor && JVMVersion.contains("1.6.0");
    }
  
    /**
     * Load the implementation of UnixOperatingSystemMXBean for Oracle jvm
     * and runs the desired method. 
     * @param mBeanMethodName : method to run from the interface UnixOperatingSystemMXBean
     * @return the method result
     */
    private Long runUnixMXBeanMethod (String mBeanMethodName) {  
      Object unixos;
      Class<?> classRef;
      Method mBeanMethod;
  
     try {
       classRef = Class.forName("com.sun.management.UnixOperatingSystemMXBean");
       if (classRef.isInstance(osMbean)) {
         mBeanMethod = classRef.getMethod(mBeanMethodName, new Class[0]);
         unixos = classRef.cast(osMbean);
         return (Long)mBeanMethod.invoke(unixos);
       }
     }
     catch(Exception e) {
       LOG.warn("Not able to load class or method for" +
           " com.sun.management.UnixOperatingSystemMXBean.", e);
     }
     return null;
   }
 
   /**
    * Get the number of opened filed descriptor for the runtime jvm.
    * If Oracle java, it will use the com.sun.management interfaces.
    * Otherwise, this methods implements it (linux only).  
    * @return number of open file descriptors for the jvm
    */
   public long getOpenFileDescriptorCount() {
 
     Long ofdc;
     
     if (!ibmvendor) {
       ofdc = runUnixMXBeanMethod("getOpenFileDescriptorCount");
       return (ofdc != null ? ofdc.longValue () : -1);
     }
     InputStream in = null;
     BufferedReader output = null;
     try {
       //need to get the PID number of the process first
       RuntimeMXBean rtmbean = ManagementFactory.getRuntimeMXBean();
       String rtname = rtmbean.getName();
       String[] pidhost = rtname.split("@");
 
       //using linux bash commands to retrieve info
       Process p = Runtime.getRuntime().exec(
       new String[] { "bash", "-c",
           "ls /proc/" + pidhost[0] + "/fdinfo | wc -l" });
       in = p.getInputStream();
       output = new BufferedReader(new InputStreamReader(in));
       String openFileDesCount;
       if ((openFileDesCount = output.readLine()) != null)      
              return Long.parseLong(openFileDesCount);
      } catch (IOException ie) {
        LOG.warn("Not able to get the number of open file descriptors", ie);
      } finally {
        if (output != null) {
          try {
            output.close();
          } catch (IOException e) {
            LOG.warn("Not able to close the InputStream", e);
          }
        }
        if (in != null){
          try {
            in.close();
          } catch (IOException e) {
            LOG.warn("Not able to close the InputStream", e);
          }
        }
     }
     return -1;
   }
 
   /**
    * @see java.lang.management.OperatingSystemMXBean#getSystemLoadAverage
    */
   public double getSystemLoadAverage() {
     return osMbean.getSystemLoadAverage();
   }
 
   /**
    * @return the physical free memory (not the JVM one, as it's not very useful as it depends on
    *  the GC), but the one from the OS as it allows a little bit more to guess if the machine is
    *  overloaded or not).
    */
   public long getFreeMemory() {
     if (ibmvendor){
       return 0;
     }
 
     Long r =  runUnixMXBeanMethod("getFreePhysicalMemorySize");
     return (r != null ? r : -1);
   }
 
 
   /**
    * Workaround to get the current number of process running. Approach is the one described here:
    * http://stackoverflow.com/questions/54686/how-to-get-a-list-of-current-open-windows-process-with-java
    */
   public int getNumberOfRunningProcess(){
     if (!isUnix()){
       return 0;
     }
 
     BufferedReader input = null;
     try {
       int count = 0;
       Process p = Runtime.getRuntime().exec("ps -e");
       input = new BufferedReader(new InputStreamReader(p.getInputStream()));
       while (input.readLine() != null) {
         count++;
       }
       return count - 1; //  -1 because there is a headline
     } catch (IOException e) {
       return -1;
     }  finally {
       if (input != null){
         try {
           input.close();
         } catch (IOException ignored) {
         }
       }
     }
   }
 
   /**
    * Get the number of the maximum file descriptors the system can use.
    * If Oracle java, it will use the com.sun.management interfaces.
    * Otherwise, this methods implements it (linux only).  
    * @return max number of file descriptors the operating system can use.
    */
   public long getMaxFileDescriptorCount() {
     Long mfdc;
     if (!ibmvendor) {
       mfdc = runUnixMXBeanMethod("getMaxFileDescriptorCount");
       return (mfdc != null ? mfdc.longValue () : -1);
     }
     InputStream in = null;
     BufferedReader output = null;
     try {
       //using linux bash commands to retrieve info
       Process p = Runtime.getRuntime().exec(new String[] { "bash", "-c", "ulimit -n" });
       in = p.getInputStream();
       output = new BufferedReader(new InputStreamReader(in));
       String maxFileDesCount;
       if ((maxFileDesCount = output.readLine()) != null) return Long.parseLong(maxFileDesCount);
     } catch (IOException ie) {
       LOG.warn("Not able to get the max number of file descriptors", ie);
     } finally {
       if (output != null) {
         try {
           output.close();
         } catch (IOException e) {
           LOG.warn("Not able to close the reader", e);
         }
       }
       if (in != null){
         try {
           in.close();
         } catch (IOException e) {
           LOG.warn("Not able to close the InputStream", e);
         }
       }
     }
     return -1;
  }
 }