UnsafeUtil.java

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//Copyright 2012 Cloudera Inc.
//
// Licensed 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 com.cloudera.impala.util;

import java.lang.reflect.Field;
import java.security.AccessController;
import java.security.PrivilegedAction;

import sun.misc.Unsafe;

@SuppressWarnings("restriction")
public class UnsafeUtil {
  // object to allow us to use unsafe APIs. This lets us read native memory without
  // copies and not have to switch back and forth between little endian and big endian.
  public static final Unsafe UNSAFE;

  // This is the offset to the start of the array data. (There's some bytes
  // before the array data like the size and other java stuff).
  private static final int BYTE_ARRAY_DATA_OFFSET;

  static {
    UNSAFE = (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 (NoSuchFieldException e) {
              throw new Error();
            } catch (IllegalAccessException e) {
              throw new Error();
            }
          }
        });

    BYTE_ARRAY_DATA_OFFSET = UNSAFE.arrayBaseOffset(byte[].class);
  }

  // Copies src[srcOffset, srcOffset + len) into dst.
  public static void Copy(long dst, byte[] src, int srcOffset, int len) {
    UNSAFE.copyMemory(src, BYTE_ARRAY_DATA_OFFSET + srcOffset, null, dst, len);
  }

  // Copies src[0, len) into dst[dstOffset, dstOffset + len).
  public static void Copy(byte[] dst, int dstOffset, long src, int len) {
    UNSAFE.copyMemory(null, src, dst, dstOffset + BYTE_ARRAY_DATA_OFFSET, len);
  }
}