UtilUnsafe.java

/*******************************************************************************
 *  	Copyright 2014,
 *  		Luis Pina <luis@luispina.me>,
 *  		Michael Hicks <mwh@cs.umd.edu>
 *  	
 *  	This file is part of Rubah.
 *
 *     Rubah is free software: you can redistribute it and/or modify
 *     it under the terms of the GNU General Public License as published by
 *     the Free Software Foundation, either version 3 of the License, or
 *     (at your option) any later version.
 *
 *     Rubah is distributed in the hope that it will be useful,
 *     but WITHOUT ANY WARRANTY; without even the implied warranty of
 *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *     GNU General Public License for more details.
 *
 *     You should have received a copy of the GNU General Public License
 *     along with Rubah.  If not, see <http://www.gnu.org/licenses/>.
 *******************************************************************************/
package org.cliffc.high_scale_lib;
import java.lang.reflect.Field;
import sun.misc.Unsafe;

/**
 * Simple class to obtain access to the {@link Unsafe} object.  {@link Unsafe}
 * is required to allow efficient CAS operations on arrays.  Note that the
 * versions in {@link java.util.concurrent.atomic}, such as {@link
 * java.util.concurrent.atomic.AtomicLongArray}, require extra memory ordering
 * guarantees which are generally not needed in these algorithms and are also
 * expensive on most processors.
 */
class UtilUnsafe {
  private UtilUnsafe() { } // dummy private constructor
  /** Fetch the Unsafe.  Use With Caution. */
  public static Unsafe getUnsafe() {
    // Not on bootclasspath
    if( UtilUnsafe.class.getClassLoader() == null )
      return Unsafe.getUnsafe();
    try {
      final Field fld = Unsafe.class.getDeclaredField("theUnsafe");
      fld.setAccessible(true);
      return (Unsafe) fld.get(UtilUnsafe.class);
    } catch (Exception e) {
      throw new RuntimeException("Could not obtain access to sun.misc.Unsafe", e);
    }
  }
}