content: // Protocol Buffers - Google's data interchange format
  // Copyright 2008 Google Inc.  All rights reserved.
  // https://developers.google.com/protocol-buffers/
  //
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are
  // met:
  //
  //     * Redistributions of source code must retain the above copyright
  // notice, this list of conditions and the following disclaimer.
  //     * Redistributions in binary form must reproduce the above
  // copyright notice, this list of conditions and the following disclaimer
  // in the documentation and/or other materials provided with the
  // distribution.
  //     * Neither the name of Google Inc. nor the names of its
  // contributors may be used to endorse or promote products derived from
  // this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  package com.google.protobuf;
  
  import sun.misc.Unsafe;
  
  import java.lang.reflect.Field;
  import java.nio.Buffer;
  import java.nio.ByteBuffer;
  import java.security.AccessController;
  import java.security.PrivilegedExceptionAction;
  
  /**
   * Utility class for working with unsafe operations.
   */
  // TODO(nathanmittler): Add support for Android Memory/MemoryBlock
  final class UnsafeUtil {
    private static final sun.misc.Unsafe UNSAFE = getUnsafe();
    private static final boolean HAS_UNSAFE_BYTEBUFFER_OPERATIONS =
        supportsUnsafeByteBufferOperations();
    private static final boolean HAS_UNSAFE_ARRAY_OPERATIONS = supportsUnsafeArrayOperations();
    private static final long ARRAY_BASE_OFFSET = byteArrayBaseOffset();
    private static final long BUFFER_ADDRESS_OFFSET = fieldOffset(field(Buffer.class, "address"));
  
    private UnsafeUtil() {
    }
  
    static boolean hasUnsafeArrayOperations() {
      return HAS_UNSAFE_ARRAY_OPERATIONS;
    }
  
    static boolean hasUnsafeByteBufferOperations() {
      return HAS_UNSAFE_BYTEBUFFER_OPERATIONS;
    }
  
    static long getArrayBaseOffset() {
      return ARRAY_BASE_OFFSET;
    }
  
    static byte getByte(byte[] target, long offset) {
      return UNSAFE.getByte(target, offset);
    }
  
    static void putByte(byte[] target, long offset, byte value) {
      UNSAFE.putByte(target, offset, value);
    }
  
    static void copyMemory(
        byte[] src, long srcOffset, byte[] target, long targetOffset, long length) {
      UNSAFE.copyMemory(src, srcOffset, target, targetOffset, length);
    }
  
    static long getLong(byte[] target, long offset) {
      return UNSAFE.getLong(target, offset);
    }
  
    static byte getByte(long address) {
      return UNSAFE.getByte(address);
    }
  
    static void putByte(long address, byte value) {
      UNSAFE.putByte(address, value);
    }
  
    static long getLong(long address) {
      return UNSAFE.getLong(address);
    }
  
    static void copyMemory(long srcAddress, long targetAddress, long length) {
      UNSAFE.copyMemory(srcAddress, targetAddress, length);
    }
  
    /**
     * Gets the offset of the {@code address} field of the given direct {@link ByteBuffer}.
     */
    static long addressOffset(ByteBuffer buffer) {
      return UNSAFE.getLong(buffer, BUFFER_ADDRESS_OFFSET);
    }
  
    /**
     * Gets the {@code sun.misc.Unsafe} instance, or {@code null} if not available on this platform.
     */
    private static sun.misc.Unsafe getUnsafe() {
      sun.misc.Unsafe unsafe = null;
      try {
        unsafe =
            AccessController.doPrivileged(
                new PrivilegedExceptionAction<Unsafe>() {
                  @Override
                  public sun.misc.Unsafe run() throws Exception {
                    Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
  
                    for (Field f : k.getDeclaredFields()) {
                      f.setAccessible(true);
                      Object x = f.get(null);
                      if (k.isInstance(x)) {
                        return k.cast(x);
                      }
                    }
                    // The sun.misc.Unsafe field does not exist.
                    return null;
                  }
                });
      } catch (Throwable e) {
        // Catching Throwable here due to the fact that Google AppEngine raises NoClassDefFoundError
        // for Unsafe.
      }
      return unsafe;
    }
  
    /**
     * Indicates whether or not unsafe array operations are supported on this platform.
     */
    private static boolean supportsUnsafeArrayOperations() {
      boolean supported = false;
      if (UNSAFE != null) {
        try {
          Class<?> clazz = UNSAFE.getClass();
          clazz.getMethod("arrayBaseOffset", Class.class);
          clazz.getMethod("getByte", Object.class, long.class);
          clazz.getMethod("putByte", Object.class, long.class, byte.class);
          clazz.getMethod("getLong", Object.class, long.class);
          clazz.getMethod(
              "copyMemory", Object.class, long.class, Object.class, long.class, long.class);
          supported = true;
        } catch (Throwable e) {
          // Do nothing.
        }
      }
      return supported;
    }
  
    private static boolean supportsUnsafeByteBufferOperations() {
      boolean supported = false;
      if (UNSAFE != null) {
        try {
          Class<?> clazz = UNSAFE.getClass();
          clazz.getMethod("objectFieldOffset", Field.class);
          clazz.getMethod("getByte", long.class);
          clazz.getMethod("getLong", Object.class, long.class);
          clazz.getMethod("putByte", long.class, byte.class);
          clazz.getMethod("getLong", long.class);
          clazz.getMethod("copyMemory", long.class, long.class, long.class);
          supported = true;
        } catch (Throwable e) {
          // Do nothing.
        }
      }
      return supported;
    }
  
    /**
     * Get the base offset for byte arrays, or {@code -1} if {@code sun.misc.Unsafe} is not available.
     */
    private static int byteArrayBaseOffset() {
      return HAS_UNSAFE_ARRAY_OPERATIONS ? UNSAFE.arrayBaseOffset(byte[].class) : -1;
    }
  
    /**
     * Returns the offset of the provided field, or {@code -1} if {@code sun.misc.Unsafe} is not
     * available.
     */
    private static long fieldOffset(Field field) {
      return field == null || UNSAFE == null ? -1 : UNSAFE.objectFieldOffset(field);
    }
  
    /**
     * Gets the field with the given name within the class, or {@code null} if not found. If found,
     * the field is made accessible.
     */
    private static Field field(Class<?> clazz, String fieldName) {
      Field field;
      try {
        field = clazz.getDeclaredField(fieldName);
        field.setAccessible(true);
      } catch (Throwable t) {
        // Failed to access the fields.
        field = null;
      }
      return field;
    }
  }
  