/**
    * 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.reflect.Field;
  import java.lang.reflect.Method;
  import java.security.AccessController;
  import java.security.PrivilegedAction;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  
  @InterfaceAudience.Private
  public class UnsafeAvailChecker {
  
    private static final String CLASS_NAME = "sun.misc.Unsafe";
    private static final Log LOG = LogFactory.getLog(UnsafeAvailChecker.class);
    private static boolean avail = false;
    private static boolean unaligned = false;
  
    static {
      avail = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
        @Override
        public Boolean run() {
          try {
            Class<?> clazz = Class.forName(CLASS_NAME);
            Field f = clazz.getDeclaredField("theUnsafe");
            f.setAccessible(true);
            Object theUnsafe = f.get(null);
            if (theUnsafe == null) {
              LOG.warn("Could not get static instance from sun.misc.Unsafe");
              return false;
            }
            // Check for availability of all methods used by UnsafeAccess
            Method m;
            try {
              m = clazz.getDeclaredMethod("arrayBaseOffset", Class.class);
              if (m == null) {
                LOG.warn("sun.misc.Unsafe is missing arrayBaseOffset(Class)");
                return false;
              }
              m = clazz.getDeclaredMethod("copyMemory", Object.class, long.class, Object.class,
                long.class, long.class);
              if (m == null) {
                LOG.warn("sun.misc.Unsafe is missing copyMemory(Object,long,Object,long,long)");
                return false;
              }
              m = clazz.getDeclaredMethod("getByte", Object.class, long.class);
              if (m == null) {
                LOG.warn("sun.misc.Unsafe is missing getByte(Object,long)");
                return false;
              }
              m = clazz.getDeclaredMethod("getShort", long.class);
              if (m == null) {
                LOG.warn("sun.misc.Unsafe is missing getShort(long)");
                return false;
              }
              m = clazz.getDeclaredMethod("getShort", Object.class, long.class);
              if (m == null) {
                LOG.warn("sun.misc.Unsafe is missing getShort(Object,long)");
                return false;
              }
              m = clazz.getDeclaredMethod("getInt", long.class);
              if (m == null) {
                LOG.warn("sun.misc.Unsafe is missing getInt(long)");
                return false;
              }
              m = clazz.getDeclaredMethod("getInt", Object.class, long.class);
              if (m == null) {
                LOG.warn("sun.misc.Unsafe is missing getInt(Object,long)");
                return false;
              }
              m = clazz.getDeclaredMethod("getLong", long.class);
              if (m == null) {
                LOG.warn("sun.misc.Unsafe is missing getLong(long)");
                return false;
              }
              m = clazz.getDeclaredMethod("getLong", Object.class, long.class);
              if (m == null) {
                LOG.warn("sun.misc.Unsafe is missing getLong(Object,long)");
                return false;
              }
              m = clazz.getDeclaredMethod("putByte", long.class, byte.class);
             if (m == null) {
               LOG.warn("sun.misc.Unsafe is missing putByte(long,byte)");
               return false;
             }
             m = clazz.getDeclaredMethod("putByte", Object.class, long.class, byte.class);
             if (m == null) {
               LOG.warn("sun.misc.Unsafe is missing putByte(Object,long,byte)");
               return false;
             }
             m = clazz.getDeclaredMethod("putShort", long.class, short.class);
             if (m == null) {
               LOG.warn("sun.misc.Unsafe is missing putShort(long,short)");
               return false;
             }
             m = clazz.getDeclaredMethod("putShort", Object.class, long.class, short.class);
             if (m == null) {
               LOG.warn("sun.misc.Unsafe is missing putShort(Object,long,short)");
               return false;
             }
             m = clazz.getDeclaredMethod("putInt", long.class, int.class);
             if (m == null) {
               LOG.warn("sun.misc.Unsafe is missing putInt(long,int)");
               return false;
             }
             m = clazz.getDeclaredMethod("putInt", Object.class, long.class, int.class);
             if (m == null) {
               LOG.warn("sun.misc.Unsafe is missing putInt(Object,long,int)");
               return false;
             }
             m = clazz.getDeclaredMethod("putLong", long.class, long.class);
             if (m == null) {
               LOG.warn("sun.misc.Unsafe is missing putLong(long,long)");
               return false;
             }
             m = clazz.getDeclaredMethod("putLong", Object.class, long.class, long.class);
             if (m == null) {
               LOG.warn("sun.misc.Unsafe is missing putLong(Object,long,long)");
               return false;
             }
             // theUnsafe is accessible and all methods are available
             return true;
           } catch (Throwable e) {
             LOG.warn("sun.misc.Unsafe is missing one or more required methods", e);
           }
         } catch (Throwable e) {
           LOG.warn("sun.misc.Unsafe is not available/accessible", e);
         }
         return false;
       }
     });
     // When Unsafe itself is not available/accessible consider unaligned as false.
     if (avail) {
       String arch = System.getProperty("os.arch");
       if ("ppc64".equals(arch) || "ppc64le".equals(arch)) {
         // java.nio.Bits.unaligned() wrongly returns false on ppc (JDK-8165231),
         unaligned = true;
       } else {
         try {
           // Using java.nio.Bits#unaligned() to check for unaligned-access capability
           Class<?> clazz = Class.forName("java.nio.Bits");
           Method m = clazz.getDeclaredMethod("unaligned");
           m.setAccessible(true);
           unaligned = (Boolean) m.invoke(null);
         } catch (Exception e) {
           LOG.warn("java.nio.Bits#unaligned() check failed."
               + "Unsafe based read/write of primitive types won't be used", e);
         }
       }
     }
   }
 
   /**
    * @return true when running JVM is having sun's Unsafe package available in it and it is
    *         accessible.
    */
   public static boolean isAvailable() {
     return avail;
   }
 
   /**
    * @return true when running JVM is having sun's Unsafe package available in it and underlying
    *         system having unaligned-access capability.
    */
   public static boolean unaligned() {
     return unaligned;
   }
 
   private UnsafeAvailChecker() {
     // private constructor to avoid instantiation
   }
 }