/**
    * 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.nio.ByteBuffer;
  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;
  import sun.nio.ch.DirectBuffer;
  
  @InterfaceAudience.Private
  @InterfaceStability.Evolving
  @edu.umd.cs.findbugs.annotations.SuppressWarnings(value="REC_CATCH_EXCEPTION",
    justification="If exception, presume unaligned")
  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 long BYTE_ARRAY_BASE_OFFSET;
  
    public static final boolean LITTLE_ENDIAN =
      ByteOrder.nativeOrder().equals(ByteOrder.LITTLE_ENDIAN);
  
    // This number limits the number of bytes to copy per call to Unsafe's
    // copyMemory method. A limit is imposed to allow for safepoint polling
    // during a large copy
    static final long UNSAFE_COPY_THRESHOLD = 1024L * 1024L;
    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);
      } else{
        BYTE_ARRAY_BASE_OFFSET = -1;
      }
    }
  
    private UnsafeAccess(){}
  
    // APIs to copy data. This will be direct memory location copy and will be much faster
    /**
     * Copies the bytes from given array's offset to length part into the given buffer.
     * @param src
     * @param srcOffset
     * @param dest
     * @param destOffset
     * @param length
     */
    public static void copy(byte[] src, int srcOffset, ByteBuffer dest, int destOffset, int length) {
      long destAddress = destOffset;
      Object destBase = null;
      if (dest.isDirect()) {
        destAddress = destAddress + ((DirectBuffer) dest).address();
      } else {
        destAddress = destAddress + BYTE_ARRAY_BASE_OFFSET + dest.arrayOffset();
        destBase = dest.array();
      }
      long srcAddress = (long) srcOffset + BYTE_ARRAY_BASE_OFFSET;
      unsafeCopy(src, srcAddress, destBase, destAddress, length);
    }
  
   private static void unsafeCopy(Object src, long srcAddr, Object dst, long destAddr, long len) {
     while (len > 0) {
       long size = (len > UNSAFE_COPY_THRESHOLD) ? UNSAFE_COPY_THRESHOLD : len;
       theUnsafe.copyMemory(src, srcAddr, dst, destAddr, size);
       len -= size;
       srcAddr += size;
       destAddr += size;
     }
   }
 
   /**
    * Copies specified number of bytes from given offset of {@code src} ByteBuffer to the
    * {@code dest} array.
    *
    * @param src
    * @param srcOffset
    * @param dest
    * @param destOffset
    * @param length
    */
   public static void copy(ByteBuffer src, int srcOffset, byte[] dest, int destOffset,
       int length) {
     long srcAddress = srcOffset;
     Object srcBase = null;
     if (src.isDirect()) {
       srcAddress = srcAddress + ((DirectBuffer) src).address();
     } else {
       srcAddress = srcAddress + BYTE_ARRAY_BASE_OFFSET + src.arrayOffset();
       srcBase = src.array();
     }
     long destAddress = (long) destOffset + BYTE_ARRAY_BASE_OFFSET;
     unsafeCopy(srcBase, srcAddress, dest, destAddress, length);
   }
 
   /**
    * Copies specified number of bytes from given offset of {@code src} buffer into the {@code dest}
    * buffer.
    *
    * @param src
    * @param srcOffset
    * @param dest
    * @param destOffset
    * @param length
    */
   public static void copy(ByteBuffer src, int srcOffset, ByteBuffer dest, int destOffset,
       int length) {
     long srcAddress, destAddress;
     Object srcBase = null, destBase = null;
     if (src.isDirect()) {
       srcAddress = srcOffset + ((DirectBuffer) src).address();
     } else {
       srcAddress = (long) srcOffset +  src.arrayOffset() + BYTE_ARRAY_BASE_OFFSET;
       srcBase = src.array();
     }
     if (dest.isDirect()) {
       destAddress = destOffset + ((DirectBuffer) dest).address();
     } else {
       destAddress = (long) destOffset + BYTE_ARRAY_BASE_OFFSET + dest.arrayOffset();
       destBase = dest.array();
     }
     unsafeCopy(srcBase, srcAddress, destBase, destAddress, length);
   }
 
   // APIs to read primitive data from a byte[] using Unsafe way
   /**
    * Converts a byte array to a short value considering it was written in big-endian format.
    * @param bytes byte array
    * @param offset offset into array
    * @return the short value
    */
   public static short toShort(byte[] bytes, int offset) {
     if (LITTLE_ENDIAN) {
       return Short.reverseBytes(theUnsafe.getShort(bytes, offset + BYTE_ARRAY_BASE_OFFSET));
     } else {
       return theUnsafe.getShort(bytes, offset + BYTE_ARRAY_BASE_OFFSET);
     }
   }
 
   /**
    * Converts a byte array to an int value considering it was written in big-endian format.
    * @param bytes byte array
    * @param offset offset into array
    * @return the int value
    */
   public static int toInt(byte[] bytes, int offset) {
     if (LITTLE_ENDIAN) {
       return Integer.reverseBytes(theUnsafe.getInt(bytes, offset + BYTE_ARRAY_BASE_OFFSET));
     } else {
       return theUnsafe.getInt(bytes, offset + BYTE_ARRAY_BASE_OFFSET);
     }
   }
 
   /**
    * Converts a byte array to a long value considering it was written in big-endian format.
    * @param bytes byte array
    * @param offset offset into array
    * @return the long value
    */
   public static long toLong(byte[] bytes, int offset) {
     if (LITTLE_ENDIAN) {
       return Long.reverseBytes(theUnsafe.getLong(bytes, offset + BYTE_ARRAY_BASE_OFFSET));
     } else {
       return theUnsafe.getLong(bytes, offset + BYTE_ARRAY_BASE_OFFSET);
     }
   }
 
   // APIs to write primitive data to a byte[] using Unsafe way
   /**
    * Put a short value out to the specified byte array position in big-endian format.
    * @param bytes the byte array
    * @param offset position in the array
    * @param val short to write out
    * @return incremented offset
    */
   public static int putShort(byte[] bytes, int offset, short val) {
     if (LITTLE_ENDIAN) {
       val = Short.reverseBytes(val);
     }
     theUnsafe.putShort(bytes, offset + BYTE_ARRAY_BASE_OFFSET, val);
     return offset + Bytes.SIZEOF_SHORT;
   }
 
   /**
    * Put an int value out to the specified byte array position in big-endian format.
    * @param bytes the byte array
    * @param offset position in the array
    * @param val int to write out
    * @return incremented offset
    */
   public static int putInt(byte[] bytes, int offset, int val) {
     if (LITTLE_ENDIAN) {
       val = Integer.reverseBytes(val);
     }
     theUnsafe.putInt(bytes, offset + BYTE_ARRAY_BASE_OFFSET, val);
     return offset + Bytes.SIZEOF_INT;
   }
 
   /**
    * Put a long value out to the specified byte array position in big-endian format.
    * @param bytes the byte array
    * @param offset position in the array
    * @param val long to write out
    * @return incremented offset
    */
   public static int putLong(byte[] bytes, int offset, long val) {
     if (LITTLE_ENDIAN) {
       val = Long.reverseBytes(val);
     }
     theUnsafe.putLong(bytes, offset + BYTE_ARRAY_BASE_OFFSET, val);
     return offset + Bytes.SIZEOF_LONG;
   }
 
   // APIs to read primitive data from a ByteBuffer using Unsafe way
   /**
    * Reads a short value at the given buffer's offset considering it was written in big-endian
    * format.
    *
    * @param buf
    * @param offset
    * @return short value at offset
    */
   public static short toShort(ByteBuffer buf, int offset) {
     if (LITTLE_ENDIAN) {
       return Short.reverseBytes(getAsShort(buf, offset));
     }
     return getAsShort(buf, offset);
   }
 
   /**
    * Reads bytes at the given offset as a short value.
    * @param buf
    * @param offset
    * @return short value at offset
    */
   static short getAsShort(ByteBuffer buf, int offset) {
     if (buf.isDirect()) {
       return theUnsafe.getShort(((DirectBuffer) buf).address() + offset);
     }
     return theUnsafe.getShort(buf.array(), BYTE_ARRAY_BASE_OFFSET + buf.arrayOffset() + offset);
   }
 
   /**
    * Reads an int value at the given buffer's offset considering it was written in big-endian
    * format.
    *
    * @param buf
    * @param offset
    * @return int value at offset
    */
   public static int toInt(ByteBuffer buf, int offset) {
     if (LITTLE_ENDIAN) {
       return Integer.reverseBytes(getAsInt(buf, offset));
     }
     return getAsInt(buf, offset);
   }
 
   /**
    * Reads bytes at the given offset as an int value.
    * @param buf
    * @param offset
    * @return int value at offset
    */
   static int getAsInt(ByteBuffer buf, int offset) {
     if (buf.isDirect()) {
       return theUnsafe.getInt(((DirectBuffer) buf).address() + offset);
     }
     return theUnsafe.getInt(buf.array(), BYTE_ARRAY_BASE_OFFSET + buf.arrayOffset() + offset);
   }
 
   /**
    * Reads a long value at the given buffer's offset considering it was written in big-endian
    * format.
    *
    * @param buf
    * @param offset
    * @return long value at offset
    */
   public static long toLong(ByteBuffer buf, int offset) {
     if (LITTLE_ENDIAN) {
       return Long.reverseBytes(getAsLong(buf, offset));
     }
     return getAsLong(buf, offset);
   }
 
   /**
    * Reads bytes at the given offset as a long value.
    * @param buf
    * @param offset
    * @return long value at offset
    */
   static long getAsLong(ByteBuffer buf, int offset) {
     if (buf.isDirect()) {
       return theUnsafe.getLong(((DirectBuffer) buf).address() + offset);
     }
     return theUnsafe.getLong(buf.array(), BYTE_ARRAY_BASE_OFFSET + buf.arrayOffset() + offset);
   }
 
   /**
    * Put an int value out to the specified ByteBuffer offset in big-endian format.
    * @param buf the ByteBuffer to write to
    * @param offset offset in the ByteBuffer
    * @param val int to write out
    * @return incremented offset
    */
   public static int putInt(ByteBuffer buf, int offset, int val) {
     if (LITTLE_ENDIAN) {
       val = Integer.reverseBytes(val);
     }
     if (buf.isDirect()) {
       theUnsafe.putInt(((DirectBuffer) buf).address() + offset, val);
     } else {
       theUnsafe.putInt(buf.array(), offset + buf.arrayOffset() + BYTE_ARRAY_BASE_OFFSET, val);
     }
     return offset + Bytes.SIZEOF_INT;
   }
 
   // APIs to add primitives to BBs
   /**
    * Put a short value out to the specified BB position in big-endian format.
    * @param buf the byte buffer
    * @param offset position in the buffer
    * @param val short to write out
    * @return incremented offset
    */
   public static int putShort(ByteBuffer buf, int offset, short val) {
     if (LITTLE_ENDIAN) {
       val = Short.reverseBytes(val);
     }
     if (buf.isDirect()) {
       theUnsafe.putShort(((DirectBuffer) buf).address() + offset, val);
     } else {
       theUnsafe.putShort(buf.array(), BYTE_ARRAY_BASE_OFFSET + buf.arrayOffset() + offset, val);
     }
     return offset + Bytes.SIZEOF_SHORT;
   }
 
   /**
    * Put a long value out to the specified BB position in big-endian format.
    * @param buf the byte buffer
    * @param offset position in the buffer
    * @param val long to write out
    * @return incremented offset
    */
   public static int putLong(ByteBuffer buf, int offset, long val) {
     if (LITTLE_ENDIAN) {
       val = Long.reverseBytes(val);
     }
     if (buf.isDirect()) {
       theUnsafe.putLong(((DirectBuffer) buf).address() + offset, val);
     } else {
       theUnsafe.putLong(buf.array(), BYTE_ARRAY_BASE_OFFSET + buf.arrayOffset() + offset, val);
     }
     return offset + Bytes.SIZEOF_LONG;
   }
 
   /**
    * Put a byte value out to the specified BB position in big-endian format.
    * @param buf the byte buffer
    * @param offset position in the buffer
    * @param b byte to write out
    * @return incremented offset
    */
   public static int putByte(ByteBuffer buf, int offset, byte b) {
     if (buf.isDirect()) {
       theUnsafe.putByte(((DirectBuffer) buf).address() + offset, b);
     } else {
       theUnsafe.putByte(buf.array(),
         BYTE_ARRAY_BASE_OFFSET + buf.arrayOffset() + offset, b);
     }
     return offset + 1;
   }
 
   /**
    * Returns the byte at the given offset
    * @param buf the buffer to read
    * @param offset the offset at which the byte has to be read
    * @return the byte at the given offset
    */
   public static byte toByte(ByteBuffer buf, int offset) {
     if (buf.isDirect()) {
       return theUnsafe.getByte(((DirectBuffer) buf).address() + offset);
     } else {
       return theUnsafe.getByte(buf.array(), BYTE_ARRAY_BASE_OFFSET + buf.arrayOffset() + offset);
     }
   }
 }