java线程阻塞中断和LockSupport的常见问题

   转载自 http://www.iteye.com/topic/970055

    上周五和周末，工作忙里偷闲，在看java cocurrent中也顺便再温故了一下Thread.interrupt和java 5之后的LockSupport的实现。

 

在介绍之前，先抛几个问题。

 

1. Thread.interrupt()方法和InterruptedException异常的关系？是由interrupt触发产生了InterruptedException异常？
2. Thread.interrupt()会中断线程什么状态的工作？ RUNNING or BLOCKING？
3. 一般Thread编程需要关注interrupt中断不？一般怎么处理？可以用来做什么？
4. LockSupport.park()和unpark()，与object.wait()和notify()的区别？
5. LockSupport.park(Object blocker)传递的blocker对象做什么用？
6. LockSupport能响应Thread.interrupt()事件不？会抛出InterruptedException异常？
7. Thread.interrupt()处理是否有对应的回调函数？类似于钩子调用？

如果你都都能很明确的答上来了，说明你已经完全懂Thread.interrupt，可以不用往下看那了。

那如果不清楚的，带着这几个问题，一起来梳理下。

Thread的interrupt处理的几个方法：

• public void interrupt() :  执行线程interrupt事件
• public boolean isInterrupted() : 检查当前线程是否处于interrupt
• public static boolean interrupted() ： check当前线程是否处于interrupt，并重置interrupt信息。类似于resetAndGet()

理解：

1. 每个线程都有一个interrupt status标志位，用于表明当前线程是否处于中断状态

2. 一般调用Thread.interrupt()会有两种处理方式

• 遇到一个低优先级的block状态时，比如object.wait(),object.sleep(),object.join()。它会立马触发一个unblock解除阻塞，并throw一个InterruptedException。
• 其他情况，Thread.interrupt()仅仅只是更新了status标志位。然后你的工作线程通过Thread.isInterrrupted()进行检查，可以做相应的处理，比如也throw InterruptedException或者是清理状态，取消task等。

在interrupt javadoc中描述：

最佳实践

IBM上有篇文章写的挺不错。 Java theory and practice: Dealing with InterruptedException , 里面提到了Interrupt处理的几条最佳实践。

1. Don't swallow interrupts （别吃掉Interrupt，一般是两种处理：  继续throw InterruptedException异常。  另一种就是继续设置Thread.interupt()异常标志位，让更上一层去进行相应处理。
   

   public class TaskRunner implements Runnable {
        private BlockingQueue<Task> queue;
   
        public TaskRunner(BlockingQueue<Task> queue) {
            this.queue = queue;
       }
   
        public void run() {
            try {
                 while (true) {
                     Task task = queue.take(10, TimeUnit.SECONDS);
                    task.execute();
                }
            }
             catch (InterruptedException e) {
                 // Restore the interrupted status
                Thread.currentThread().interrupt();
            }
       }
   }

   public class TaskRunner implements Runnable {
       private BlockingQueue<Task> queue;
   
       public TaskRunner(BlockingQueue<Task> queue) { 
           this.queue = queue; 
       }
   
       public void run() { 
           try {
                while (true) {
                    Task task = queue.take(10, TimeUnit.SECONDS);
                    task.execute();
                }
            }
            catch (InterruptedException e) { 
                // Restore the interrupted status
                Thread.currentThread().interrupt();
            }
       }
   }

    
2. Implementing cancelable tasks with Interrupt (使用Thread.interrupt()来设计和支持可被cancel的task)
   

   public class PrimeProducer extends Thread {
        private final BlockingQueue<BigInteger> queue;
   
       PrimeProducer(BlockingQueue<BigInteger> queue) {
            this.queue = queue;
       }
   
        public void run() {
            try {
               BigInteger p = BigInteger.ONE;
                while (!Thread.currentThread().isInterrupted())
                   queue.put(p = p.nextProbablePrime());
            } catch (InterruptedException consumed) {
                /* Allow thread to exit */
           }
       }
   
        public void cancel() { interrupt(); } // 发起中断
    }<SPAN style="WHITE-SPACE: normal"> </SPAN>

   public class PrimeProducer extends Thread {
       private final BlockingQueue<BigInteger> queue;
   
       PrimeProducer(BlockingQueue<BigInteger> queue) {
           this.queue = queue;
       }
   
       public void run() {
           try {
               BigInteger p = BigInteger.ONE;
               while (!Thread.currentThread().isInterrupted())
                   queue.put(p = p.nextProbablePrime());
           } catch (InterruptedException consumed) {
               /* Allow thread to exit */
           }
       }
   
       public void cancel() { interrupt(); } // 发起中断
   } 

注册Interrupt处理事件(非正常用法)

一般正常的task设计用来处理cancel，都是采用主动轮询的方式检查Thread.isInterrupt()，对业务本身存在一定的嵌入性，还有就是存在延迟，你得等到下一个检查点(谁知道下一个检查点是在什么时候，特别是进行一个socket.read时，遇到过一个HttpClient超时的问题)。

 

来看一下，主动抛出InterruptedException异常的实现，借鉴于InterruptibleChannel的设计，比较取巧。

 

 

interface InterruptAble { // 定义可中断的接口

     public void interrupt() throws InterruptedException;
}

 abstract class InterruptSupport implements InterruptAble {

     private volatile boolean interrupted = false;
     private Interruptible    interruptor = new Interruptible() {

                                              public void interrupt() {
                                                  interrupted = true;
                                                  InterruptSupport.this.interrupt(); // 位置3
                                             }
                                         };

     public final boolean execute() throws InterruptedException {
         try {
             blockedOn(interruptor); // 位置1
             if (Thread.currentThread().isInterrupted()) { // 立马被interrupted
                interruptor.interrupt();
            }
             // 执行业务代码
            bussiness();
         } finally {
             blockedOn(null);   // 位置2
        }

         return interrupted;
    }

     public abstract void bussiness() ;

     public abstract void interrupt();

     // -- sun.misc.SharedSecrets --
     static void blockedOn(Interruptible intr) { // package-private
        sun.misc.SharedSecrets.getJavaLangAccess().blockedOn(Thread.currentThread(), intr);
    }
}

interface InterruptAble { // 定义可中断的接口

    public void interrupt() throws InterruptedException;
}

abstract class InterruptSupport implements InterruptAble {

    private volatile boolean interrupted = false;
    private Interruptible    interruptor = new Interruptible() {

                                             public void interrupt() {
                                                 interrupted = true;
                                                 InterruptSupport.this.interrupt(); // 位置3
                                             }
                                         };

    public final boolean execute() throws InterruptedException {
        try {
            blockedOn(interruptor); // 位置1
            if (Thread.currentThread().isInterrupted()) { // 立马被interrupted
                interruptor.interrupt();
            }
            // 执行业务代码
            bussiness();
        } finally {
            blockedOn(null);   // 位置2
        }

        return interrupted;
    }

    public abstract void bussiness() ;

    public abstract void interrupt();

    // -- sun.misc.SharedSecrets --
    static void blockedOn(Interruptible intr) { // package-private
        sun.misc.SharedSecrets.getJavaLangAccess().blockedOn(Thread.currentThread(), intr);
    }
}

 

代码说明，几个取巧的点：

位置1：利用sun提供的blockedOn方法，绑定对应的Interruptible事件处理钩子到指定的Thread上。

位置2：执行完代码后，清空钩子。避免使用连接池时，对下一个Thread处理事件的影响。

位置3：定义了Interruptible事件钩子的处理方法，回调InterruptSupport.this.interrupt()方法，子类可以集成实现自己的业务逻辑，比如sock流关闭等等。

 

使用: 

 

class InterruptRead extends InterruptSupport {

     private FileInputStream in;

     @Override
     public void bussiness() {
         File file = new File("/dev/urandom"); // 读取linux黑洞，永远读不完
         try {
             in = new FileInputStream(file);
             byte[] bytes = new byte[1024];
             while (in.read(bytes, 0, 1024) > 0) {
                 // Thread.sleep(100);
                 // if (Thread.interrupted()) {// 以前的Interrupt检查方式
                 // throw new InterruptedException("");
                 // }
            }
         } catch (Exception e) {
             throw new RuntimeException(e);
        }
    }

     public FileInputStream getIn() {
         return in;
    }

     @Override
     public void interrupt() {
         try {
            in.getChannel().close();
         } catch (IOException e) {
            e.printStackTrace();
        }
    }

}

 public static void main(String args[]) throws Exception {
         final InterruptRead test = new InterruptRead();
         Thread t = new Thread() {

             @Override
             public void run() {
                 long start = System.currentTimeMillis();
                 try {
                     System.out.println("InterruptRead start!");
                    test.execute();
                 } catch (InterruptedException e) {
                     System.out.println("InterruptRead end! cost time : " + (System.currentTimeMillis() - start));
                    e.printStackTrace();
                }
            }
        };
        t.start();
         // 先让Read执行3秒
         Thread.sleep(3000);
         // 发出interrupt中断
        t.interrupt();
    }

class InterruptRead extends InterruptSupport {

    private FileInputStream in;

    @Override
    public void bussiness() {
        File file = new File("/dev/urandom"); // 读取linux黑洞，永远读不完
        try {
            in = new FileInputStream(file);
            byte[] bytes = new byte[1024];
            while (in.read(bytes, 0, 1024) > 0) {
                // Thread.sleep(100);
                // if (Thread.interrupted()) {// 以前的Interrupt检查方式
                // throw new InterruptedException("");
                // }
            }
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public FileInputStream getIn() {
        return in;
    }

    @Override
    public void interrupt() {
        try {
            in.getChannel().close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}

public static void main(String args[]) throws Exception {
        final InterruptRead test = new InterruptRead();
        Thread t = new Thread() {

            @Override
            public void run() {
                long start = System.currentTimeMillis();
                try {
                    System.out.println("InterruptRead start!");
                    test.execute();
                } catch (InterruptedException e) {
                    System.out.println("InterruptRead end! cost time : " + (System.currentTimeMillis() - start));
                    e.printStackTrace();
                }
            }
        };
        t.start();
        // 先让Read执行3秒
        Thread.sleep(3000);
        // 发出interrupt中断
        t.interrupt();
    }

 

 

jdk源码介绍： 

1. sun提供的钩子可以查看System的相关代码, line : 1125

 

sun.misc.SharedSecrets.setJavaLangAccess(new sun.misc.JavaLangAccess(){
            public sun.reflect.ConstantPool getConstantPool(Class klass) {
                return klass.getConstantPool();
            }
            public void setAnnotationType(Class klass, AnnotationType type) {
                klass.setAnnotationType(type);
            }
            public AnnotationType getAnnotationType(Class klass) {
                return klass.getAnnotationType();
            }
            public <E extends Enum<E>>
            E[] getEnumConstantsShared(Class<E> klass) {
                return klass.getEnumConstantsShared();
            }
            public void blockedOn(Thread t, Interruptible b) {
                t.blockedOn(b);
            }
        });

sun.misc.SharedSecrets.setJavaLangAccess(new sun.misc.JavaLangAccess(){
            public sun.reflect.ConstantPool getConstantPool(Class klass) {
                return klass.getConstantPool();
            }
            public void setAnnotationType(Class klass, AnnotationType type) {
                klass.setAnnotationType(type);
            }
            public AnnotationType getAnnotationType(Class klass) {
                return klass.getAnnotationType();
            }
            public <E extends Enum<E>>
		    E[] getEnumConstantsShared(Class<E> klass) {
                return klass.getEnumConstantsShared();
            }
            public void blockedOn(Thread t, Interruptible b) {
                t.blockedOn(b);
            }
        });

 

 2. Thread.interrupt()

 

public void interrupt() {
     if (this != Thread.currentThread())
        checkAccess();

     synchronized (blockerLock) {
        Interruptible b = blocker;
         if (b != null) {
         interrupt0();       // Just to set the interrupt flag
         b.interrupt(); //回调钩子
         return;
        }
    }
    interrupt0();
    }

public void interrupt() {
	if (this != Thread.currentThread())
	    checkAccess();

	synchronized (blockerLock) {
	    Interruptible b = blocker;
	    if (b != null) {
		interrupt0();		// Just to set the interrupt flag
		b.interrupt(); //回调钩子
		return;
	    }
	}
	interrupt0();
    }

 

 

更多

更多关于Thread.stop,suspend,resume,interrupt的使用注意点，可以看一下sun的文档,比如http://download.oracle.com/javase/6/docs/technotes/guides/concurrency/threadPrimitiveDeprecation.html

 

 

最后来解答一下之前的几个问题：

问题1： Thread.interrupt()方法和InterruptedException异常的关系？是由interrupt触发产生了InterruptedException异常？ 

答： Thread.interrupt()只是在Object.wait() .Object.join(), Object.sleep()几个方法会主动抛出InterruptedException异常。而在其他的的block常见，只是通过设置了Thread的一个标志位信息，需要程序自我进行处理。

 

if (Thread.interrupted())  // Clears interrupted status!
     throw new InterruptedException();

if (Thread.interrupted())  // Clears interrupted status!
    throw new InterruptedException();

 

问题2：Thread.interrupt()会中断线程什么状态的工作？ RUNNING or BLOCKING？

答：Thread.interrupt设计的目的主要是用于处理线程处于block状态，比如wait(),sleep()状态就是个例子。但可以在程序设计时为支持task cancel，同样可以支持RUNNING状态。比如Object.join()和一些支持interrupt的一些nio channel设计。

 

问题3： 一般Thread编程需要关注interrupt中断不？一般怎么处理？可以用来做什么？

答： interrupt用途： unBlock操作，支持任务cancel， 数据清理等。

 

问题4： LockSupport.park()和unpark()，与object.wait()和notify()的区别？

答：

1.  面向的主体不一样。LockSuport主要是针对Thread进进行阻塞处理，可以指定阻塞队列的目标对象，每次可以指定具体的线程唤醒。Object.wait()是以对象为纬度，阻塞当前的线程和唤醒单个(随机)或者所有线程。

2.  实现机制不同。虽然LockSuport可以指定monitor的object对象，但和object.wait()，两者的阻塞队列并不交叉。可以看下测试例子。object.notifyAll()不能唤醒LockSupport的阻塞Thread.

 

 

 

问题5： LockSupport.park(Object blocker)传递的blocker对象做什么用？

答: 对应的blcoker会记录在Thread的一个parkBlocker属性中,通过jstack命令可以非常方便的监控具体的阻塞对象.

 

public static void park(Object blocker) {
        Thread t = Thread.currentThread();
         setBlocker(t, blocker); // 设置Thread.parkBlocker属性的值
         unsafe.park(false, 0L);
         setBlocker(t, null);  // 清除Thread.parkBlocker属性的值
    }

public static void park(Object blocker) {
        Thread t = Thread.currentThread();
        setBlocker(t, blocker); // 设置Thread.parkBlocker属性的值
        unsafe.park(false, 0L);
        setBlocker(t, null);  // 清除Thread.parkBlocker属性的值
    }

 具体LockSupport的javadoc描述也比较清楚,可以看下:

 

 

问题6： LockSupport能响应Thread.interrupt()事件不？会抛出InterruptedException异常？

答：能响应interrupt事件，但不会抛出InterruptedException异常。针对LockSupport对Thread.interrupte支持，也先看一下javadoc中的描述：

 

相关测试代码

 

package com.agapple.cocurrent;

 import java.io.File;
 import java.io.FileInputStream;
 import java.lang.reflect.Field;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.locks.LockSupport;

 public class LockSupportTest {

     private static LockSupportTest blocker = new LockSupportTest();

     public static void main(String args[]) throws Exception {
        lockSupportTest();
        parkTest();
        interruptParkTest();
        interruptSleepTest();
        interruptWaitTest();
    }

     /**
     * LockSupport.park对象后，尝试获取Thread.blocker对象，调用其single唤醒
     *
     * @throws Exception
     */
     private static void lockSupportTest() throws Exception {
         Thread t = doTest(new TestCallBack() {

             @Override
             public void callback() throws Exception {
                 // 尝试sleep 5s
                 System.out.println("blocker");
                LockSupport.park(blocker);
                 System.out.println("wakeup now!");
            }

             @Override
             public String getName() {
                 return "lockSupportTest";
            }

        });
         t.start(); // 启动读取线程

         Thread.sleep(150);
         synchronized (blocker) {
             Field field = Thread.class.getDeclaredField("parkBlocker");
             field.setAccessible(true);
            Object fBlocker = field.get(t);
            System.out.println(blocker == fBlocker);
             Thread.sleep(100);
             System.out.println("notifyAll");
            blocker.notifyAll();
        }
    }

     /**
     * 尝试去中断一个object.wait()，会抛出对应的InterruptedException异常
     *
     * @throws InterruptedException
     */
     private static void interruptWaitTest() throws InterruptedException {
         final Object obj = new Object();
         Thread t = doTest(new TestCallBack() {

             @Override
             public void callback() throws Exception {
                 // 尝试sleep 5s
                obj.wait();
                 System.out.println("wakeup now!");
            }

             @Override
             public String getName() {
                 return "interruptWaitTest";
            }

        });
         t.start(); // 启动读取线程
         Thread.sleep(2000);
         t.interrupt(); // 检查下在park时，是否响应中断
    }

     /**
     * 尝试去中断一个Thread.sleep()，会抛出对应的InterruptedException异常
     *
     * @throws InterruptedException
     */
     private static void interruptSleepTest() throws InterruptedException {
         Thread t = doTest(new TestCallBack() {

             @Override
             public void callback() throws Exception {
                 // 尝试sleep 5s
                 Thread.sleep(5000);
                 System.out.println("wakeup now!");
            }

             @Override
             public String getName() {
                 return "interruptSleepTest";
            }

        });
         t.start(); // 启动读取线程
         Thread.sleep(2000);
         t.interrupt(); // 检查下在park时，是否响应中断
    }

     /**
     * 尝试去中断一个LockSupport.park()，会有响应但不会抛出InterruptedException异常
     *
     * @throws InterruptedException
     */
     private static void interruptParkTest() throws InterruptedException {
         Thread t = doTest(new TestCallBack() {

             @Override
             public void callback() {
                 // 尝试去park 自己线程
                 LockSupport.parkNanos(blocker, TimeUnit.SECONDS.toNanos(5));
                 System.out.println("wakeup now!");
            }

             @Override
             public String getName() {
                 return "interruptParkTest";
            }

        });
         t.start(); // 启动读取线程
         Thread.sleep(2000);
         t.interrupt(); // 检查下在park时，是否响应中断
    }

     /**
     * 尝试去中断一个LockSupport.unPark()，会有响应
     *
     * @throws InterruptedException
     */
     private static void parkTest() throws InterruptedException {
         Thread t = doTest(new TestCallBack() {

             @Override
             public void callback() {
                 // 尝试去park 自己线程
                LockSupport.park(blocker);
                 System.out.println("wakeup now!");
            }

             @Override
             public String getName() {
                 return "parkTest";
            }

        });

         t.start(); // 启动读取线程
         Thread.sleep(2000);
        LockSupport.unpark(t);
        t.interrupt();
    }

     public static Thread doTest(final TestCallBack call) {
         return new Thread() {

             @Override
             public void run() {
                 File file = new File("/dev/urandom"); // 读取linux黑洞
                 try {
                     FileInputStream in = new FileInputStream(file);
                     byte[] bytes = new byte[1024];
                     while (in.read(bytes, 0, 1024) > 0) {
                         if (Thread.interrupted()) {
                             throw new InterruptedException("");
                        }
                         System.out.println(bytes[0]);
                         Thread.sleep(100);
                         long start = System.currentTimeMillis();
                        call.callback();
                         System.out.println(call.getName() + " callback finish cost : "
                                           + (System.currentTimeMillis() - start));
                    }
                 } catch (Exception e) {
                    e.printStackTrace();
                }
            }

        };
    }
}

 interface TestCallBack {

     public void callback() throws Exception;

     public String getName();
}

package com.agapple.cocurrent;

import java.io.File;
import java.io.FileInputStream;
import java.lang.reflect.Field;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.LockSupport;

public class LockSupportTest {

    private static LockSupportTest blocker = new LockSupportTest();

    public static void main(String args[]) throws Exception {
        lockSupportTest();
        parkTest();
        interruptParkTest();
        interruptSleepTest();
        interruptWaitTest();
    }

    /**
     * LockSupport.park对象后，尝试获取Thread.blocker对象，调用其single唤醒
     * 
     * @throws Exception
     */
    private static void lockSupportTest() throws Exception {
        Thread t = doTest(new TestCallBack() {

            @Override
            public void callback() throws Exception {
                // 尝试sleep 5s
                System.out.println("blocker");
                LockSupport.park(blocker);
                System.out.println("wakeup now!");
            }

            @Override
            public String getName() {
                return "lockSupportTest";
            }

        });
        t.start(); // 启动读取线程

        Thread.sleep(150);
        synchronized (blocker) {
            Field field = Thread.class.getDeclaredField("parkBlocker");
            field.setAccessible(true);
            Object fBlocker = field.get(t);
            System.out.println(blocker == fBlocker);
            Thread.sleep(100);
            System.out.println("notifyAll");
            blocker.notifyAll();
        }
    }

    /**
     * 尝试去中断一个object.wait()，会抛出对应的InterruptedException异常
     * 
     * @throws InterruptedException
     */
    private static void interruptWaitTest() throws InterruptedException {
        final Object obj = new Object();
        Thread t = doTest(new TestCallBack() {

            @Override
            public void callback() throws Exception {
                // 尝试sleep 5s
                obj.wait();
                System.out.println("wakeup now!");
            }

            @Override
            public String getName() {
                return "interruptWaitTest";
            }

        });
        t.start(); // 启动读取线程
        Thread.sleep(2000);
        t.interrupt(); // 检查下在park时，是否响应中断
    }

    /**
     * 尝试去中断一个Thread.sleep()，会抛出对应的InterruptedException异常
     * 
     * @throws InterruptedException
     */
    private static void interruptSleepTest() throws InterruptedException {
        Thread t = doTest(new TestCallBack() {

            @Override
            public void callback() throws Exception {
                // 尝试sleep 5s
                Thread.sleep(5000);
                System.out.println("wakeup now!");
            }

            @Override
            public String getName() {
                return "interruptSleepTest";
            }

        });
        t.start(); // 启动读取线程
        Thread.sleep(2000);
        t.interrupt(); // 检查下在park时，是否响应中断
    }

    /**
     * 尝试去中断一个LockSupport.park()，会有响应但不会抛出InterruptedException异常
     * 
     * @throws InterruptedException
     */
    private static void interruptParkTest() throws InterruptedException {
        Thread t = doTest(new TestCallBack() {

            @Override
            public void callback() {
                // 尝试去park 自己线程
                LockSupport.parkNanos(blocker, TimeUnit.SECONDS.toNanos(5));
                System.out.println("wakeup now!");
            }

            @Override
            public String getName() {
                return "interruptParkTest";
            }

        });
        t.start(); // 启动读取线程
        Thread.sleep(2000);
        t.interrupt(); // 检查下在park时，是否响应中断
    }

    /**
     * 尝试去中断一个LockSupport.unPark()，会有响应
     * 
     * @throws InterruptedException
     */
    private static void parkTest() throws InterruptedException {
        Thread t = doTest(new TestCallBack() {

            @Override
            public void callback() {
                // 尝试去park 自己线程
                LockSupport.park(blocker);
                System.out.println("wakeup now!");
            }

            @Override
            public String getName() {
                return "parkTest";
            }

        });

        t.start(); // 启动读取线程
        Thread.sleep(2000);
        LockSupport.unpark(t);
        t.interrupt();
    }

    public static Thread doTest(final TestCallBack call) {
        return new Thread() {

            @Override
            public void run() {
                File file = new File("/dev/urandom"); // 读取linux黑洞
                try {
                    FileInputStream in = new FileInputStream(file);
                    byte[] bytes = new byte[1024];
                    while (in.read(bytes, 0, 1024) > 0) {
                        if (Thread.interrupted()) {
                            throw new InterruptedException("");
                        }
                        System.out.println(bytes[0]);
                        Thread.sleep(100);
                        long start = System.currentTimeMillis();
                        call.callback();
                        System.out.println(call.getName() + " callback finish cost : "
                                           + (System.currentTimeMillis() - start));
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }

        };
    }
}

interface TestCallBack {

    public void callback() throws Exception;

    public String getName();
}

 

 

最后

发觉文章越写越长,那就索性发到了论坛,大家一起讨论下.毕竟文章中描述的都是一些使用层面的东东,并没有从操作系统或者sun native实现上去介绍Thread的一些机制,熟悉这块的大牛门也可以出来发表下高见.

 

本文仅当抛砖引玉,欢迎发言!