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The Netty project is an effort to provide an asynchronous event-driven network application framework and tools for rapid development of maintainable high performance and high scalability protocol servers and clients. In other words, Netty is a NIO client server framework which enables quick and easy development of network applications such as protocol servers and clients. It greatly simplifies and streamlines network programming such as TCP and UDP socket server.

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/*
 * Copyright 2012 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 org.jboss.netty.util.internal;

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

/**
 * Utility that detects various properties specific to the current runtime
 * environment, such as Java version and the availability of the
 * {@code sun.misc.Unsafe} object.
 *
 * 

 * You can disable the use of {@code sun.misc.Unsafe} if you specify
 * the System property org.jboss.netty.tryUnsafe with
 * value of {@code false}. Default is {@code true}.
 */
public final class DetectionUtil {

    private static final int JAVA_VERSION = javaVersion0();
    private static final boolean HAS_UNSAFE = hasUnsafe(AtomicInteger.class.getClassLoader());
    private static final boolean IS_WINDOWS;
    static {
        String os = SystemPropertyUtil.get("os.name", "").toLowerCase();
        // windows
        IS_WINDOWS =  os.contains("win");
    }

    /**
     * Return {@code true} if the JVM is running on Windows
     *
     */
    public static boolean isWindows() {
        return IS_WINDOWS;
    }

    public static boolean hasUnsafe() {
        return HAS_UNSAFE;
    }

    public static int javaVersion() {
        return JAVA_VERSION;
    }

    private static boolean hasUnsafe(ClassLoader loader) {
        boolean noUnsafe = SystemPropertyUtil.getBoolean("io.netty.noUnsafe", false);
        if (noUnsafe) {
            return false;
        }

        // Legacy properties
        boolean tryUnsafe;
        if (SystemPropertyUtil.contains("io.netty.tryUnsafe")) {
            tryUnsafe = SystemPropertyUtil.getBoolean("io.netty.tryUnsafe", true);
        } else {
            tryUnsafe = SystemPropertyUtil.getBoolean("org.jboss.netty.tryUnsafe", true);
        }

        if (!tryUnsafe) {
            return false;
        }

        try {
            Class unsafeClazz = Class.forName("sun.misc.Unsafe", true, loader);
            return hasUnsafeField(unsafeClazz);
        } catch (Exception e) {
            // Ignore
        }

        return false;
    }

    private static boolean hasUnsafeField(final Class unsafeClass) throws PrivilegedActionException {
        return AccessController.doPrivileged(new PrivilegedExceptionAction() {
            public Boolean run() throws Exception {
                unsafeClass.getDeclaredField("theUnsafe");
                return true;
            }
        });
    }

    private static int javaVersion0() {
        try {
            // Check if its android, if so handle it the same way as java6.
            //
            // See https://github.com/netty/netty/issues/282
            Class.forName("android.app.Application");
            return 6;
        } catch (ClassNotFoundException e) {
            //Ignore
        }

        try {
            Class.forName(
                    "java.util.concurrent.LinkedTransferQueue", false,
                    BlockingQueue.class.getClassLoader());
            return 7;
        } catch (Exception e) {
            // Ignore
        }

        try {
            Class.forName(
                    "java.util.ArrayDeque", false, Queue.class.getClassLoader());
            return 6;
        } catch (Exception e) {
            // Ignore
        }

        return 5;
    }

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