/*
 ***** BEGIN LICENSE BLOCK *****
 * Version: EPL 2.0/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Eclipse Public
 * 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.eclipse.org/legal/epl-v20.html
 *
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
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 * either of the GNU General Public License Version 2 or later (the "GPL"),
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package org.jruby.util.unsafe;

import org.jruby.javasupport.Java;

import java.lang.reflect.Field;

public final class UnsafeHolder {
    
    private UnsafeHolder(){}
        
    /**
     * Holds a reference to Unsafe if available, null otherwise.    
     */
    public static final sun.misc.Unsafe U = loadUnsafe();
    
    private static sun.misc.Unsafe loadUnsafe() {
        try {
            Class unsafeClass = Class.forName("sun.misc.Unsafe");
            Field f = unsafeClass.getDeclaredField("theUnsafe");
            Java.trySetAccessible(f);
            return (sun.misc.Unsafe) f.get(null);
        } catch (Exception e) {
            return null;
        } catch (NoClassDefFoundError ncdfe) {
            // Google AppEngine raises NCDFE for Unsafe rather than CNFE
            return null;
        }
    }
    
    public static long fieldOffset(Class clazz, String name) {
        if(U == null)
            return -1;
        try {
            return U.objectFieldOffset(clazz.getDeclaredField(name));
        } catch (Exception e) {
            return sun.misc.Unsafe.INVALID_FIELD_OFFSET;
        }
    }
}
