/**
    * 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.nio.ByteOrder;
  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;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  
  import sun.misc.Unsafe;
  
  @InterfaceAudience.Private
  @InterfaceStability.Evolving
  public final class UnsafeAccess {
  
    private static final Log LOG = LogFactory.getLog(UnsafeAccess.class);
  
    public static final Unsafe theUnsafe;
  
    /** The offset to the first element in a byte array. */
    public static final int BYTE_ARRAY_BASE_OFFSET;
    private static boolean unaligned = false;
  
    static {
      theUnsafe = (Unsafe) AccessController.doPrivileged(new PrivilegedAction<Object>() {
        @Override
        public Object run() {
          try {
            Field f = Unsafe.class.getDeclaredField("theUnsafe");
            f.setAccessible(true);
            return f.get(null);
          } catch (Throwable e) {
            LOG.warn("sun.misc.Unsafe is not accessible", e);
          }
          return null;
        }
      });
  
      if(theUnsafe != null){
        BYTE_ARRAY_BASE_OFFSET = theUnsafe.arrayBaseOffset(byte[].class);
        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) {
          unaligned = false;
        }
      } else{
        BYTE_ARRAY_BASE_OFFSET = -1;
      }
    }
  
    private UnsafeAccess(){}
    
    public static boolean isAvailable() {
      return theUnsafe != null;
    }
  
    /**
     * @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;
    }
  
    public static final boolean littleEndian = ByteOrder.nativeOrder()
        .equals(ByteOrder.LITTLE_ENDIAN);
  }