Java多线程Runnable与Callable区别与拓展

我们先来分别看一下这两个接口

Runnable:

 //
 // Source code recreated from a .class file by IntelliJ IDEA
 // (powered by Fernflower decompiler)
 //

 package java.lang;

 @FunctionalInterface
 public interface Runnable {
     void run();
 }

只有一个方法run(),表示执行任务的逻辑。

Callable:

 //
 // Source code recreated from a .class file by IntelliJ IDEA
 // (powered by Fernflower decompiler)
 //

 package java.util.concurrent;

 @FunctionalInterface
 public interface Callable<V> {
     V call() throws Exception;
 }

也只有一个方法call(),但是是一个有返回值的方法，这给我们提供了获取方法执行结果的可能，即使它是个异步的任务，它可以获取异常，给我们极大地便利知道任务执行失败的原因。

Runnable例子Demo:

 package cn.concurrent.executor;

 /**
  * Created by spark on 17-9-24.
  */
 public class RunnabelDemo implements Runnable {

     public RunnabelDemo(String acceptStr) {
         this.acceptStr = acceptStr;
     }

     private String acceptStr;

     @Override
     public void run() {
         try {
             // 线程阻塞 1 秒，此时有异常产生，只能在方法内部消化，无法上抛
             Thread.sleep(1000);
         } catch (InterruptedException e) {
             e.printStackTrace();
         }
         // 最终处理结果无法返回
         System.out.println("hello : " + this.acceptStr);
     }

     public static void main(String[] args) {
         Runnable runnable = new RunnabelDemo("my runable test!");
         long beginTime = System.currentTimeMillis();
         new Thread(runnable).start();
         long endTime = System.currentTimeMillis();
         System.out.println("cast : " + (endTime - beginTime) / 1000 + " second!");
     }
 }

结果：

 /usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -javaagent:/usr/local/idea/lib/idea_rt.jar=41745:/usr/local/idea/bin -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/spark/IdeaProjects/thread/thread/target/classes:/home/spark/.m2/repository/com/lmax/disruptor/3.3.2/disruptor-3.3.2.jar cn.concurrent.executor.RunnabelDemo
 cast : 0 second!
 hello : my runable test!

 Process finished with exit code 0

Callable的例子:

 package cn.concurrent.executor;

 import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Future;
 import java.util.concurrent.FutureTask;

 /**
  * Created by spark on 17-9-24.
  */
 public class CallableDemo implements Callable<String> {

     private String name;

     public CallableDemo(String name) {
         this.name = name;
     }

     @Override
     public String call() throws Exception {
         //执行任务的相关逻辑
         Thread.sleep(1000);
         return name + " : this is task is successed.";
     }

     public static void main(String[] args) throws ExecutionException, InterruptedException {
         CallableDemo callableDemo = new CallableDemo("wade");
         //异步执行的结果
         FutureTask<String> future = new FutureTask<String>(callableDemo);
         new Thread(future).start();
         //調用get()方法--阻塞
         String result=future.get();
         System.out.println("hello : " + result);
     }
 }

结果:

 /usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -javaagent:/usr/local/idea/lib/idea_rt.jar=37879:/usr/local/idea/bin -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/spark/IdeaProjects/thread/thread/target/classes:/home/spark/.m2/repository/com/lmax/disruptor/3.3.2/disruptor-3.3.2.jar cn.concurrent.executor.CallableDemo
 hello : wade : this is task is successed.

 Process finished with exit code 0

问题:如何把一个Runnbale的任务转变为有返回值的Callable的任务。

^_^我们有工具类Executors可以帮我们实现,如下图：

其中Executors.callable(Runnable),就是我们需要的方法，是不是很简单呢。

代码如下:

 package cn.concurrent.executor;

 import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Executors;
 import java.util.concurrent.FutureTask;

 /**
  * Created by spark on 17-9-24.
  */
 public class RunnableToCallable implements Runnable {

     String name;

     public RunnableToCallable(String name) {
         this.name = name;
     }

     @Override
     public void run() {
         try {
             Thread.sleep(1000);
             System.out.println(name + " :任务执行完毕！");
         } catch (InterruptedException e) {
             e.printStackTrace();
         }
     }

     public static void main(String[] args) throws ExecutionException, InterruptedException {
         RunnableToCallable task=new RunnableToCallable("wade");
         //转变为有返回值的任务
         Callable<Object> future=Executors.callable(task);
         FutureTask<Object> futureTask=new FutureTask<Object>(future);
         new Thread(futureTask).start();
         //調用get()方法--阻塞
         Object result=futureTask.get();
         System.out.println("hello : " + result);
     }
 }

结果如下：

 /usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -javaagent:/usr/local/idea/lib/idea_rt.jar=36136:/usr/local/idea/bin -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/spark/IdeaProjects/thread/thread/target/classes:/home/spark/.m2/repository/com/lmax/disruptor/3.3.2/disruptor-3.3.2.jar cn.concurrent.executor.RunnableToCallable
 wade :任务执行完毕！
 hello : null

 Process finished with exit code 0

说明:因为该任务没有返回结果，因此返回的为null.

接下来我们讨论一下ExecutorService.executr()与ExecutorService.submit()方法的区别。

类图如下：

从类图可以看到：

execute只能接受Runnable类型的任务，并且没有返回值。

submit不管是Runnable还是Callable类型的任务都可以接受，但是Runnable返回值均为void，所以使用Future的get()获得的还是null

然后来看异常处理：

对于Runnable 只能通过try-catch来捕获异常，对于Callable,直接抛出就可以，然后在get的时候捕获异常进行处理。

如下：

 package cn.concurrent.executor;

 import java.util.concurrent.*;

 /**
  * Created by spark on 17-9-24.
  */
 public class ThreadExceptionTest {

     public static void main(String[] args) {
         ExecutorService executorService = Executors.newCachedThreadPool();
         CallableTest callableTest = new CallableTest();
         Future<Boolean> task = executorService.submit(callableTest);
         try {
             Boolean b = task.get();
         } catch (InterruptedException e) {
             e.printStackTrace();
         } catch (ExecutionException e) {
             e.printStackTrace();
         }

     }

     static class CallableTest implements Callable<Boolean> {

         @Override
         public Boolean call() throws Exception {
             int num = 3 / 0;
             return false;
         }
     }
 }

结果：

 /usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -javaagent:/usr/local/idea/lib/idea_rt.jar=42960:/usr/local/idea/bin -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/spark/IdeaProjects/thread/thread/target/classes:/home/spark/.m2/repository/com/lmax/disruptor/3.3.2/disruptor-3.3.2.jar cn.concurrent.executor.ThreadExceptionTest
 java.util.concurrent.ExecutionException: java.lang.ArithmeticException: / by zero
     at java.util.concurrent.FutureTask.report(FutureTask.java:122)
     at java.util.concurrent.FutureTask.get(FutureTask.java:192)
     at cn.concurrent.executor.ThreadExceptionTest.main(ThreadExceptionTest.java:16)
 Caused by: java.lang.ArithmeticException: / by zero
     at cn.concurrent.executor.ThreadExceptionTest$CallableTest.call(ThreadExceptionTest.java:29)
     at cn.concurrent.executor.ThreadExceptionTest$CallableTest.call(ThreadExceptionTest.java:25)
     at java.util.concurrent.FutureTask.run(FutureTask.java:266)
     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
     at java.lang.Thread.run(Thread.java:748)

 Process finished with exit code 0

get()方法会捕获异常。

接下来，我们详细了解一下Future接口，实现类FutureTask(它有三种状态，分别为未启动，已启动，已完成);

类图如下：

1.首先可以看到，它也是一个线程，可以直接继承它来运行任务，然后交给ExecutorService执行。

如下：

 package cn.concurrent.executor;

 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.FutureTask;

 /**
  * Created by spark on 17-9-24.
  */
 public class FutureTaskDemo extends FutureTask<String> {
     public FutureTaskDemo(Runnable runnable, String s) {
         super(runnable, s);
         System.out.println(s);
     }

     @Override
     public void run() {
         try {
             Thread.sleep(1000);
             System.out.println("this is running.");
         } catch (InterruptedException e) {
             e.printStackTrace();
         }
     }

     public static void main(String[] args) {
         FutureTaskDemo futureTaskDemo = new FutureTaskDemo(new Runnable() {
             @Override
             public void run() {
                 System.out.println("this is wade.");
             }
         }, "wade");

         ExecutorService es = Executors.newFixedThreadPool(1);
         FutureTask<String> task = (FutureTask<String>) es.submit(futureTaskDemo);
         System.out.println("hello:"+task);
         es.shutdown();
     }
 }

结果如下：

 /usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -javaagent:/usr/local/idea/lib/idea_rt.jar=46018:/usr/local/idea/bin -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/spark/IdeaProjects/thread/thread/target/classes:/home/spark/.m2/repository/com/lmax/disruptor/3.3.2/disruptor-3.3.2.jar cn.concurrent.executor.FutureTaskDemo
 wade
 hello:java.util.concurrent.FutureTask@266474c2
 this is running.

 Process finished with exit code 0

2.看一下run()方法

     public void run() {
             /**
             *首先判断任务的状态 如果任务的状态不是new 说明任务的状态已经改变（说明他已经走了4种可能变化的一种）
             * 如果状态是new就会把 当前执行任务的线程付给runner, 这里用的cmpandset如果runner不为空 说明已经有线程在执行
         * 任务也会退出执行,如果状态是new并且runner为空并且把当前的线程付给了runner那么就继续执行任务(runner state 都是 volatile
             *类型的变量是一个很轻量机的线程安全操作)
             *引起state状态变化的原因 就是调用了cancel 或是 run
             **/
             if (state != NEW ||
                 !UNSAFE.compareAndSwapObject(this, runnerOffset,
                                              null, Thread.currentThread()))
                 return;  

             //开始执行任务
             try {
                 Callable<V> c = callable;
                 /**
                 * 如果 要执行的任务不为空 并且状态 new 就执行 

                 ***/
                 if (c != null && state == NEW) {
                     V result;
                     boolean ran;
                     try {
                         //执行任务
                         result = c.call();
                         //如果没有意外发生就执行成功了
                         ran = true;
                     } catch (Throwable ex) {
                             //有异常
                         result = null;
                         ran = false;
                         //设置异常
                         setException(ex);
                     }
                     //如果转型成功了 设置结果
                     if (ran)
                         (result);
                 }
             } finally {
                 // runner must be non-null until state is settled to
                 // prevent concurrent calls to run()
                 //不管是否执行成功了 都把runner设置成null
                 runner = null;
                 // state must be re-read after nulling runner to prevent
                 // leaked interrupts
                 int s = state;
                 if (s >= INTERRUPTING)
                     handlePossibleCancellationInterrupt(s);
             }
         }  

Task执行后如果成功会调用set()方法,如果有异常会调用setException()方法。

我们先看下set方法 ：

     protected void set(V v) {
             /**
             *如过state是new 把state设置成 COMPLETING
             *
             **/  

           if (UNSAFE.compareAndSwapInt(this, stateOffset, NEW, COMPLETING)) {
               outcome = v;
               //将任务设置成NORMAL   over the task
               UNSAFE.putOrderedInt(this, stateOffset, NORMAL); // final state
               finishCompletion();
           }
       }  

最后，来看一下最重要的方法get();

public V get() throws InterruptedException, ExecutionException {
        int s = state;
　　　　　//当线程状态为新建活着执行中时一直调用awaitDone方法
        if (s <= COMPLETING)
　　　　　　  //循环判断线程状态是否已经执行成功，如果执行成功返回线程状态；其中还包括线程取消，中断等情况的判断。可参见下方源码。
　　　　　　  //所以这里便是上面例子中为什么线程执行成功后即可立即得到结果，如果还没有执行成功
            s = awaitDone(false, 0L);

　　　　　　　//线程状态正常返回结果
            return report(s); 
    }

如果get时,FutureTask的状态为未完成状态，则调用awaitDone方法进行阻塞。awaitDone():

 private int awaitDone(boolean timed, long nanos)
        throws InterruptedException {
        //计算一下需要等待的时间，有可能为0，为0的话就无限期等待。
        final long deadline = timed ? System.nanoTime() + nanos : 0L;
        //一个等待节点
        WaitNode q = null;
        //是否加入队列
        boolean queued = false;
        for (;;) {
            //如果当且调用get方法的线程被interrupt 那么就把当前线程从等待队列remove
            //然后抛出异常
            if (Thread.interrupted()) {
                removeWaiter(q);
                throw new InterruptedException();
            }
            int s = state;
            //如果任务已经完成 不管是被暂停了 还是出现异常了 只要状态大于COMPLETING就返回。
            if (s > COMPLETING) {
                if (q != null)
                    q.thread = null;
                return s;
            }
            else if (s == COMPLETING) // cannot time out yet
            //如果任务正在完成中(注意是ING进行时) 那么让出一会CPU时间在继续执行
                Thread.yield();
            else if (q == null)
                //创建等待节点
                q = new WaitNode();
            else if (!queued)
                //第一次创建的等待节点需要加入等待队列，这里加入队列等待。
                queued = UNSAFE.compareAndSwapObject(this, waitersOffset,
                                                     q.next = waiters, q);
            else if (timed) {
                //如果设置了等待 那么就得锁住线程等待，如果时间到了就返回状态。
                //方法 public V get(long timeout, TimeUnit unit) 这里会根据状态做后续处理。
                nanos = deadline - System.nanoTime();
                if (nanos <= 0L) {
                    removeWaiter(q);
                    return state;
                }
                LockSupport.parkNanos(this, nanos);
            }
            else
                //否则锁住线程等待其他线程解锁。
                LockSupport.park(this);
        }
    }

awaitDone方法可以看成是不断轮询查看FutureTask的状态。在get阻塞期间：

• 如果执行get的线程被中断，则移除FutureTask的所有阻塞队列中的线程（waiters）,并抛出中断异常；

• 如果FutureTask的状态转换为完成状态（正常完成或取消），则返回完成状态；

• 如果FutureTask的状态变为COMPLETING, 则说明正在set结果，此时让线程等一等；

• 如果FutureTask的状态为初始态NEW，则将当前线程加入到FutureTask的阻塞线程中去；

• 如果get方法没有设置超时时间，则阻塞当前调用get线程；如果设置了超时时间，则判断是否达到超时时间，如果到达，则移除FutureTask的所有阻塞列队中的线程，并返回此时FutureTask的状态，如果未到达时间，则在剩下的时间内继续阻塞当前线程。

详细了解这几个方法：

当FutureTask处于未启动或者已启动状态时，执行Future.get()方法，将导致调用线程阻塞，当FutureTask处于已完成状态时，执行Future.get()方法时，将调用线程立即返回结果或者抛出异常。

当FutureTask处于未启动状态时，执行Future.cancel()方法,导致此任务永远不会被执行 ；当FutureTask处于已启动状态时，执行Future.cancel()方法将以中断执行此任务线程的方式来试图停止任务;当FutureTask处于已启动状态时，执行Future.cancel(false)方法不会对正在执行此任务的线程产生影响。

说明：Future.get()方法的实现基于AbstractQueuedSynchronizer(简称为AQS)，并发包中有很多可阻塞类(如ReentrantLock)都是基于AQS实现的，AQS是一个同步框架，它提供了通用机制来原子性管理同步状态，阻塞和唤醒线程，以及维护被阻塞线程的队列，后面有专门博客介绍AQS.

博客有很多的不足，望大家指点。