org.elasticsearch.util.concurrent.highscalelib.UtilUnsafe Maven / Gradle / Ivy

Show more of this group Show more artifacts with this name
Show all versions of elasticsearch Show documentation

Elasticsearch subproject :server

There is a newer version: 8.15.1

/*
 * Licensed to Elastic Search and Shay Banon under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. Elastic Search 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.elasticsearch.util.concurrent.highscalelib;

import sun.misc.Unsafe;

import java.lang.reflect.Field;

/**
 * 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);
        }
    }
}