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/*
 * Copyright 2011 The Netty Project
 *
 * The Netty Project 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 io.netty.util;

import java.security.AccessController;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.util.concurrent.atomic.AtomicInteger;


/**
 * Utility which checks if {@value #UNSAFE} class can be found in the classpath
 * and that it can be accessed using "theUnsafe" field which is not true for all platforms, i.e Android
 * where it is called "THE_ONE".
 */
public final class UnsafeDetectUtil {

    private static final String THE_UNSAFE = "theUnsafe";
    private static final String UNSAFE = "sun.misc.Unsafe";
    private static final boolean UNSAFE_FOUND = isUnsafeFound(AtomicInteger.class.getClassLoader());

    public static boolean isUnsafeFound(ClassLoader loader) {
        try {
            Class unsafeClazz = Class.forName(UNSAFE, true, loader);
            return hasUnsafeField(unsafeClazz);
        } catch (ClassNotFoundException e) {
            return false;
        } catch (SecurityException e) {
            return false;
        } catch (PrivilegedActionException e) {
            return false;
        }
    }
    
    private static boolean hasUnsafeField(final Class unsafeClass) throws PrivilegedActionException {
        return AccessController.doPrivileged(new PrivilegedExceptionAction() {
            public Boolean run() throws Exception {
                unsafeClass.getDeclaredField(THE_UNSAFE);
                return true;
            }
        });
    }
    
    public static boolean isUnsafeFound() {
        return UNSAFE_FOUND;
    }

    private UnsafeDetectUtil() {
        // only static method supported
    }
}