（MK）并发编程精讲

package threadcoreknowledge.stopthreads;

//描述：     run方法内没有sleep或wait方法时，停止线程
public class RightWayStopThreadWithoutSleep implements Runnable {

    @Override
    public void run() {
        int num = 0;
      //通过检查线程是否已经被中断
        while (!Thread.currentThread().isInterrupted() && num <= Integer.MAX_VALUE / 2) {
            if (num % 10000 == 0) {
                System.out.println(num + "是10000的倍数");
            }
            num++;
        }
        System.out.println("任务运行结束了");
    }

    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(new RightWayStopThreadWithoutSleep());
        thread.start();
        Thread.sleep(2000);
        thread.interrupt();
    }
}

//描述：     带有sleep的中断线程的写法
public class RightWayStopThreadWithSleep {

    public static void main(String[] args) throws InterruptedException {
        Runnable runnable = () -> {
            int num = 0;
            try {
                while (num <= 300 && !Thread.currentThread().isInterrupted()) {
                    if (num % 100 == 0) {
                        System.out.println(num + "是100的倍数");
                    }
                    num++;
                }
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        };
        Thread thread = new Thread(runnable);
        thread.start();
        Thread.sleep(500);
        thread.interrupt();
    }
}

//描述：     如果在执行过程中，每次循环都会调用sleep或wait等方法，那么不需要每次迭代都检查是否已中断
public class RightWayStopThreadWithSleepEveryLoop {
    public static void main(String[] args) throws InterruptedException {
        Runnable runnable = () -> {
            int num = 0;
            try {
                while (num <= 10000) {
                    if (num % 100 == 0) {
                        System.out.println(num + "是100的倍数");
                    }
                    num++;
                    Thread.sleep(10);
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        };
        Thread thread = new Thread(runnable);
        thread.start();
        Thread.sleep(5000);
        thread.interrupt();
    }
}

//描述：     如果while里面放try/catch，会导致中断失效
public class CantInterrupt {

    public static void main(String[] args) throws InterruptedException {
        Runnable runnable = () -> {
            int num = 0;
            while (num <= 10000 && !Thread.currentThread().isInterrupted()) {
                if (num % 100 == 0) {
                    System.out.println(num + "是100的倍数");
                }
                num++;
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };
        Thread thread = new Thread(runnable);
        thread.start();
        Thread.sleep(5000);
        thread.interrupt();
    }
}

//描述：     最佳实践：catch了InterruptedExcetion之后的优先选择：在方法签名中抛出异常 那么在run()就会强制try/catch
public class RightWayStopThreadInProd implements Runnable {

    @Override
    public void run() {
        while (true && !Thread.currentThread().isInterrupted()) {
            System.out.println("go");
            try {
                throwInMethod();
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
                //保存日志、停止程序
                System.out.println("保存日志");
                e.printStackTrace();
            }
        }
    }

    private void throwInMethod() throws InterruptedException {
      		//向上抛出异常
            Thread.sleep(2000);
    }

    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(new RightWayStopThreadInProd());
        thread.start();
        Thread.sleep(1000);
        thread.interrupt();
    }
}

//描述：最佳实践2：在catch子语句中调用Thread.currentThread().interrupt()来恢复设置中断状态，以便于在后续的执行中，依然能够检查到刚才发生了中断
//回到刚才RightWayStopThreadInProd补上中断，让它跳出
public class RightWayStopThreadInProd2 implements Runnable {

    @Override
    public void run() {
        while (true) {
            if (Thread.currentThread().isInterrupted()) {
                System.out.println("Interrupted，程序运行结束");
                break;
            }
            reInterrupt();
        }
    }

    private void reInterrupt() {
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
          //中断
            Thread.currentThread().interrupt();
            e.printStackTrace();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(new RightWayStopThreadInProd2());
        thread.start();
        Thread.sleep(1000);
        thread.interrupt();
    }
}

//描述：     错误的停止方法：用stop()来停止线程，会导致线程运行一半突然停止，没办法完成一个基本单位的操作（一个连队），会造成脏数据（有的连队多领取少领取装备）。
public class StopThread implements Runnable {

    @Override
    public void run() {
        //模拟指挥军队：一共有5个连队，每个连队10人，以连队为单位，发放武器弹药，叫到号的士兵前去领取
        for (int i = 0; i < 5; i++) {
            System.out.println("连队" + i + "开始领取武器");
            for (int j = 0; j < 10; j++) {
                System.out.println(j);
                try {
                    Thread.sleep(50);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            System.out.println("连队"+i+"已经领取完毕");
        }
    }

    public static void main(String[] args) {
        Thread thread = new Thread(new StopThread());
        thread.start();
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        thread.stop();
        //会导致某个连队中某些人没有领取到
    }
}

//描述：     演示用volatile的局限：part1 看似可行,但是程序并没有停止
public class WrongWayVolatile implements Runnable {

    private volatile boolean canceled = false;

    @Override
    public void run() {
        int num = 0;
        try {
            while (num <= 100000 && !canceled) {
                if (num % 100 == 0) {
                    System.out.println(num + "是100的倍数。");
                }
                num++;
                Thread.sleep(1);
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        WrongWayVolatile r = new WrongWayVolatile();
        Thread thread = new Thread(r);
        thread.start();
        Thread.sleep(5000);
        r.canceled = true;
    }
}

package threadcoreknowledge.stopthreads.volatiledemo;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ConcurrentLinkedQueue;

//描述：     演示用volatile的局限part2 陷入阻塞时，volatile是无法停止线程的 此例中，生产者的生产速度很快，消费者消费速度慢，所以阻塞队列满了以后，生产者会阻塞，等待消费者进一步消费
public class WrongWayVolatileCantStop {

    public static void main(String[] args) throws InterruptedException {
        ArrayBlockingQueue storage = new ArrayBlockingQueue(10);

        Producer producer = new Producer(storage);
        Thread producerThread = new Thread(producer);
        producerThread.start();
        Thread.sleep(1000);

        Consumer consumer = new Consumer(storage);
        while (consumer.needMoreNums()) {
            System.out.println(consumer.storage.take()+"被消费了");
            Thread.sleep(100);
        }
        System.out.println("消费者不需要更多数据了。");

        //一旦消费不需要更多数据了，我们应该让生产者也停下来，但是实际情况是程序并没有结束
        producer.canceled=true;
        System.out.println(producer.canceled);
    }
}

class Producer implements Runnable {

    public volatile boolean canceled = false;

    BlockingQueue storage;

    public Producer(BlockingQueue storage) {
        this.storage = storage;
    }


    @Override
    public void run() {
        int num = 0;
        try {
            while (num <= 100000 && !canceled) {
                if (num % 100 == 0) {
                    storage.put(num);
                    System.out.println(num + "是100的倍数,被放到仓库中了。");
                }
                num++;
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            System.out.println("生产者结束运行");
        }
    }
}

class Consumer {

    BlockingQueue storage;

    public Consumer(BlockingQueue storage) {
        this.storage = storage;
    }

    public boolean needMoreNums() {
        if (Math.random() > 0.95) {
            return false;
        }
        return true;
    }
}

package threadcoreknowledge.stopthreads.volatiledemo;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;

//描述：     用中断来修复刚才的无尽等待问题
public class WrongWayVolatileFixed {

    public static void main(String[] args) throws InterruptedException {
        WrongWayVolatileFixed body = new WrongWayVolatileFixed();
        ArrayBlockingQueue storage = new ArrayBlockingQueue(10);

        Producer producer = body.new Producer(storage);
        Thread producerThread = new Thread(producer);
        producerThread.start();
        Thread.sleep(1000);

        Consumer consumer = body.new Consumer(storage);
        while (consumer.needMoreNums()) {
            System.out.println(consumer.storage.take() + "被消费了");
            Thread.sleep(100);
        }
        System.out.println("消费者不需要更多数据了。");

		//中断生产者线程
        producerThread.interrupt();
    }


    class Producer implements Runnable {

        BlockingQueue storage;

        public Producer(BlockingQueue storage) {
            this.storage = storage;
        }


        @Override
        public void run() {
            int num = 0;
            try {
                while (num <= 100000 && !Thread.currentThread().isInterrupted()) {
                    if (num % 100 == 0) {
                        storage.put(num);
                        System.out.println(num + "是100的倍数,被放到仓库中了。");
                    }
                    num++;
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                System.out.println("生产者结束运行");
            }
        }
    }

    class Consumer {

        BlockingQueue storage;

        public Consumer(BlockingQueue storage) {
            this.storage = storage;
        }

        public boolean needMoreNums() {
            if (Math.random() > 0.95) {
                return false;
            }
            return true;
        }
    }
}

package threadcoreknowledge.stopthreads;

//描述：     注意Thread.interrupted()方法的目标对象是“当前线程”，而不管本方法来自于哪个对象
public class RightWayInterrupted {

    public static void main(String[] args) throws InterruptedException {

        Thread threadOne = new Thread(new Runnable() {
            @Override
            public void run() {
                for (; ; ) {
                }
            }
        });

        // 启动线程
        threadOne.start();
        //设置中断标志
        threadOne.interrupt();
        //获取中断标志,true
        System.out.println("isInterrupted: " + threadOne.isInterrupted());
        //获取中断标志并重置,false
        System.out.println("isInterrupted: " + threadOne.interrupted());
        //获取中断标志并重直,false
        System.out.println("isInterrupted: " + Thread.interrupted());
        //获取中断标志,true
        System.out.println("isInterrupted: " + threadOne.isInterrupted());
        threadOne.join();
        System.out.println("Main thread is over.");
    }
}

//描述：     展示线程的NEW、RUNNABLE、Terminated状态。即使是正在运行，也是Runnable状态，而不是Running。
public class NewRunnableTerminated implements Runnable {

    public static void main(String[] args) {
        Thread thread = new Thread(new NewRunnableTerminated());
        //打印出NEW的状态
        System.out.println(thread.getState());
        thread.start();
        System.out.println(thread.getState());
        try {
            Thread.sleep(10);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //打印出RUNNABLE的状态，即使是正在运行，也是RUNNABLE，而不是RUNNING
        System.out.println(thread.getState());
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //打印出TERMINATED状态
        System.out.println(thread.getState());
    }

    @Override
    public void run() {
        for (int i = 0; i < 1000; i++) {
            System.out.println(i);
        }
    }
}

//描述：     展示Blocked, Waiting, TimedWaiting
public class BlockedWaitingTimedWaiting implements Runnable{
    public static void main(String[] args) {
        BlockedWaitingTimedWaiting runnable = new BlockedWaitingTimedWaiting();
        Thread thread1 = new Thread(runnable);
        thread1.start();
        Thread thread2 = new Thread(runnable);
        thread2.start();
        try {
            Thread.sleep(5);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //打印出Timed_Waiting状态，因为正在执行Thread.sleep(1000);
        System.out.println(thread1.getState());
        //打印出BLOCKED状态，因为thread2想拿得到sync()的锁却拿不到
        System.out.println(thread2.getState());
        try {
            Thread.sleep(1300);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //打印出WAITING状态，因为执行了wait()
        System.out.println(thread1.getState());

    }

    @Override
    public void run() {
        syn();
    }

    private synchronized void syn() {
        try {
            Thread.sleep(1000);
            wait();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

package threadcoreknowledge.threadobjectclasscommonmethods;

//描述：     演示打印main, Thread-0, Thread-1
public class CurrentThread implements Runnable {

    public static void main(String[] args) {
        new CurrentThread().run();
        new Thread(new CurrentThread()).start();
        new Thread(new CurrentThread()).start();
    }

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName());
    }
}

//main
//Thread-0
//Thread-1

package threadcoreknowledge.threadobjectclasscommonmethods;

  //描述：     证明wait只释放当前的那把锁
  public class WaitNotifyReleaseOwnMonitor {

      private static volatile Object resourceA = new Object();
      private static volatile Object resourceB = new Object();

      public static void main(String[] args) {
          Thread thread1 = new Thread(new Runnable() {
              @Override
              public void run() {
                  synchronized (resourceA) {
                      System.out.println("ThreadA got resourceA lock.");
                      synchronized (resourceB) {
                          System.out.println("ThreadA got resourceB lock.");
                          try {
                              System.out.println("ThreadA releases resourceA lock.");
                              resourceA.wait();

                          } catch (InterruptedException e) {
                              e.printStackTrace();
                          }
                      }
                  }
              }
          });

          Thread thread2 = new Thread(new Runnable() {
              @Override
              public void run() {
                  try {
                      Thread.sleep(1000);
                  } catch (InterruptedException e) {
                      e.printStackTrace();
                  }
                  synchronized (resourceA) {
                      System.out.println("ThreadB got resourceA lock.");
                      System.out.println("ThreadB tries to resourceB lock.");

                      synchronized (resourceB) {
                          System.out.println("ThreadB got resourceB lock.");
                      }
                  }
              }
          });

          thread1.start();
          thread2.start();
      }
  }
  /*
  ThreadA got resourceA lock.
  ThreadA got resourceB lock.
  ThreadA releases resourceA lock.
  ThreadB got resourceA lock.
  ThreadB tries to resourceB lock.
  打印结果完毕，程序并没有停止运行
  */

package threadcoreknowledge.threadobjectclasscommonmethods;

import java.util.ArrayList;
import java.util.Date;
import java.util.LinkedList;
import java.util.List;

//描述：     用wait/notify来实现生产者消费者模式
public class ProducerConsumerModel {
    public static void main(String[] args) {
        EventStorage eventStorage = new EventStorage();
        Producer producer = new Producer(eventStorage);
        Consumer consumer = new Consumer(eventStorage);
        new Thread(producer).start();
        new Thread(consumer).start();
    }
}

class Producer implements Runnable {

    private EventStorage storage;

    public Producer(
            EventStorage storage) {
        this.storage = storage;
    }

    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            storage.put();
        }
    }
}

class Consumer implements Runnable {

    private EventStorage storage;

    public Consumer(
            EventStorage storage) {
        this.storage = storage;
    }

    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            storage.take();
        }
    }
}

class EventStorage {

    private int maxSize;
    private LinkedList<Date> storage;

    public EventStorage() {
        maxSize = 10;
        storage = new LinkedList<>();
    }

    public synchronized void put() {
        while (storage.size() == maxSize) {
            try {
                wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        storage.add(new Date());
        System.out.println("仓库里有了" + storage.size() + "个产品。");
        notify();
    }

    public synchronized void take() {
        while (storage.size() == 0) {
            try {
                wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println("拿到了" + storage.poll() + "，现在仓库还剩下" + storage.size());
        notify();
    }
}

package threadcoreknowledge.threadobjectclasscommonmethods;

//描述：     两个线程交替打印0~100的奇偶数，用synchronized关键字实现
public class WaitNotifyPrintOddEvenSyn {

    private static int count;

    private static final Object lock = new Object();

    //新建2个线程
    //1个只处理偶数，第二个只处理奇数（用位运算）
    //用synchronized来通信
    public static void main(String[] args) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                while (count < 100) {
                    synchronized (lock) {
                        if ((count & 1) == 0) {
                            System.out.println(Thread.currentThread().getName() + ":" + count++);
                        }
                    }
                }
            }
        }, "偶数").start();

        new Thread(new Runnable() {
            @Override
            public void run() {
                while (count < 100) {
                    synchronized (lock) {
                        if ((count & 1) == 1) {
                            System.out.println(Thread.currentThread().getName() + ":" + count++);
                        }
                    }
                }
            }
        }, "奇数").start();
    }
}
//这个程序有许多的费操作，比如偶数线程连续拿到锁，但它只会执行一次if块内容，这与线程的竞争有关

package threadcoreknowledge.threadobjectclasscommonmethods;


//描述：     两个线程交替打印0~100的奇偶数，用wait和notify
public class WaitNotifyPrintOddEveWait {

    private static int count = 0;
    private static final Object lock = new Object();


    public static void main(String[] args) {
        new Thread(new TurningRunner(), "偶数").start();
        new Thread(new TurningRunner(), "奇数").start();
    }

    //1. 拿到锁，我们就打印
    //2. 打印完，唤醒其他线程，自己就休眠
    static class TurningRunner implements Runnable {

        @Override
        public void run() {
            while (count <= 100) {
                synchronized (lock) {
                    //拿到锁就打印
                    System.out.println(Thread.currentThread().getName() + ":" + count++);
                    lock.notify();
                    if (count <= 100) {
                        try {
                            //如果任务还没结束，就让出当前的锁，并休眠
                            lock.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        }
    }
}

  package threadcoreknowledge.threadobjectclasscommonmethods;

  import java.util.Date;
  import java.util.concurrent.TimeUnit;

  /**
   * 描述：     每个1秒钟输出当前时间，被中断，观察。
   * Thread.sleep()
   * TimeUnit.SECONDS.sleep()
   */
  public class SleepInterrupted implements Runnable{

      public static void main(String[] args) throws InterruptedException {
          Thread thread = new Thread(new SleepInterrupted());
          thread.start();
          Thread.sleep(6500);
          thread.interrupt();
      }
      @Override
      public void run() {
          for (int i = 0; i < 10; i++) {
              System.out.println(new Date());
              try {
                  TimeUnit.HOURS.sleep(3);
                  TimeUnit.MINUTES.sleep(25);
                  TimeUnit.SECONDS.sleep(1);
              } catch (InterruptedException e) {
                  System.out.println("我被中断了！");
                  e.printStackTrace();
              }
          }
      }
  }

package threadcoreknowledge.threadobjectclasscommonmethods;

/**
 * 描述：     演示join期间被中断的效果
 */
public class JoinInterrupt {
    public static void main(String[] args) {
        Thread mainThread = Thread.currentThread();
        Thread thread1 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    mainThread.interrupt();
                    Thread.sleep(5000);
                    System.out.println("Thread1 finished.");
                } catch (InterruptedException e) {
                    System.out.println("子线程中断");
                }
            }
        });
        thread1.start();
        System.out.println("等待子线程运行完毕");
        try {
            thread1.join();
        } catch (InterruptedException e) {
            System.out.println(Thread.currentThread().getName()+"主线程中断了");
            thread1.interrupt();
        }
        System.out.println("子线程已运行完毕");
    }

}

package threadcoreknowledge.threadobjectclasscommonmethods;

/**
 * 描述：     通过讲解join原理，分析出join的代替写法
 */
public class JoinPrinciple {

    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName() + "执行完毕");
            }
        });

        thread.start();
        System.out.println("开始等待子线程运行完毕");
        thread.join();
      //等价代码
//        synchronized (thread) {
//            thread.wait();
//        }
        System.out.println("所有子线程执行完毕");
    }
}

package threadcoreknowledge.threadobjectclasscommonmethods;

/**
 * 描述：     ID从1开始，JVM运行起来后，我们自己创建的线程的ID早已不是2.
 */
public class Id {

    public static void main(String[] args) {
        Thread thread = new Thread();
        System.out.println("主线程的ID"+Thread.currentThread().getId());
        System.out.println("子线程的ID"+thread.getId());
    }
}

package threadcoreknowledge.uncaughtexception;

import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * 描述：     自己的MyUncaughtExceptionHanlder
 */
public class MyUncaughtExceptionHandler implements Thread.UncaughtExceptionHandler {

    private String name;

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

    @Override
    public void uncaughtException(Thread t, Throwable e) {
        Logger logger = Logger.getAnonymousLogger();
        logger.log(Level.WARNING, "线程异常，终止啦" + t.getName());
        System.out.println(name + "捕获了异常" + t.getName() + "异常");
    }
}

package threadcoreknowledge.uncaughtexception;

/**
 * 描述：     使用刚才自己写的UncaughtExceptionHandler
 */
public class UseOwnUncaughtExceptionHandler implements Runnable {

    public static void main(String[] args) throws InterruptedException {
        Thread.setDefaultUncaughtExceptionHandler(new MyUncaughtExceptionHandler("捕获器1"));

        new Thread(new UseOwnUncaughtExceptionHandler(), "MyThread-1").start();
        Thread.sleep(300);
        new Thread(new UseOwnUncaughtExceptionHandler(), "MyThread-2").start();
        Thread.sleep(300);
        new Thread(new UseOwnUncaughtExceptionHandler(), "MyThread-3").start();
        Thread.sleep(300);
        new Thread(new UseOwnUncaughtExceptionHandler(), "MyThread-4").start();
    }


    @Override
    public void run() {
        throw new RuntimeException();
    }
}

package background;

/**
 * 描述：     第二章线程安全问题，演示死锁。
 */
public class MultiThreadError implements Runnable {

    int flag = 1;
    static Object o1 = new Object();
    static Object o2 = new Object();

    public static void main(String[] args) {
        MultiThreadError r1 = new MultiThreadError();
        MultiThreadError r2 = new MultiThreadError();
        r1.flag = 1;
        r2.flag = 0;
        new Thread(r1).start();
        new Thread(r2).start();
    }

    @Override
    public void run() {
        System.out.println("flag = " + flag);
        if (flag == 1) {
            synchronized (o1) {
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                synchronized (o2) {
                    System.out.println("1");
                }
            }
        }
        if (flag == 0) {
            synchronized (o2) {
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                synchronized (o1) {
                    System.out.println("0");
                }
            }
        }
    }
}

package jmm;

import java.util.concurrent.CountDownLatch;

/**
 * 描述：     演示重排序的现象 “直到达到某个条件才停止”，测试小概率事件
 */
public class OutOfOrderExecution {

    private static int x = 0, y = 0;
    private static int a = 0, b = 0;

    public static void main(String[] args) throws InterruptedException {
        int i = 0;
        for (; ; ) {
            i++;
            x = 0;
            y = 0;
            a = 0;
            b = 0;
			//闸门工具类
            CountDownLatch latch = new CountDownLatch(3);

            Thread one = new Thread(new Runnable() {
                @Override
                public void run() {
                    try {
                        latch.countDown();
                        latch.await();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    a = 1;
                    x = b;
                }
            });
            Thread two = new Thread(new Runnable() {
                @Override
                public void run() {
                    try {
                        latch.countDown();
                        latch.await();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    b = 1;
                    y = a;
                }
            });
            two.start();
            one.start();
            latch.countDown();
            one.join();
            two.join();

            String result = "第" + i + "次（" + x + "," + y + ")";
            if (x == 0 && y == 0) {
                System.out.println(result);
                break;
            } else {
                System.out.println(result);
            }
        }
    }


}
/*
程序一共有三种情况：
（1） a=1;x=b(0);b=1;y=a(1),最终结果为x=0,y=1；先执行one，后执行two
（2） b=1;y=a(0);a=1;x=b(1),最终结果为x=1,y=0；先执行two，后执行one
（3） b=1;a=1;x=b(1);y=a(1),最终结果为x=1,y=1;这种情况需要使用闸门，先执行两个线程的第一行代码
*/

package jmm;

/**
 * 描述：     演示可见性带来的问题
 */
public class FieldVisibility {

  //会出现可见性问题
     int a = 1;
     int b = 2;

    private void change() {
        a = 3;
        b = a;
    }


    private void print() {
        System.out.println("b=" + b + ";a=" + a);
    }

    public static void main(String[] args) {
        while (true) {
            FieldVisibility test = new FieldVisibility();
            new Thread(new Runnable() {
                @Override
                public void run() {
                    try {
                        Thread.sleep(1);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    test.change();
                }
            }).start();

            new Thread(new Runnable() {
                @Override
                public void run() {
                    try {
                        Thread.sleep(1);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    test.print();
                }
            }).start();
        }

    }


}
/*
a=3,b=2
a=1,b=2
a=3,b=3
a=1,b=3(出现了可见性问题，使用volatile来解决)
*/

/**
 * 描述：     使用volatile解决可见性带来的问题
 */
public class FieldVisibility {

  //会出现可见性问题
     int a = 1;
     volatile int b = 2;

    private void change() {
        a = 3;
        b = a;
    }


    private void print() {
        System.out.println("b=" + b + ";a=" + a);
    }

    public static void main(String[] args) {
        while (true) {
            FieldVisibility test = new FieldVisibility();
            new Thread(new Runnable() {
                @Override
                public void run() {
                    try {
                        Thread.sleep(1);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    test.change();
                }
            }).start();

            new Thread(new Runnable() {
                @Override
                public void run() {
                    try {
                        Thread.sleep(1);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    test.print();
                }
            }).start();
        }

    }


}
/*
a=3,b=2
a=1,b=2
a=3,b=3
a=1,b=3(这种情况就不会出现了)
*/

package jmm;


import java.util.concurrent.atomic.AtomicInteger;

/**
 * 描述：     不适用于volatile的场景
 */
public class NoVolatile implements Runnable {

    volatile int a;
  //原子变量，记录正确的结果
    AtomicInteger realA = new AtomicInteger();

    public static void main(String[] args) throws InterruptedException {
        Runnable r =  new NoVolatile();
        Thread thread1 = new Thread(r);
        Thread thread2 = new Thread(r);
        thread1.start();
        thread2.start();
        thread1.join();
        thread2.join();
        System.out.println(((NoVolatile) r).a);
        System.out.println(((NoVolatile) r).realA.get());
    }
    @Override
    public void run() {
        for (int i = 0; i < 10000; i++) {
            a++;
          //增加
            realA.incrementAndGet();
        }
    }
}

package jmm;

import java.util.concurrent.atomic.AtomicInteger;
import singleton.Singleton8;

/**
 * 描述：     volatile适用的情况1
 */
public class UseVolatile1 implements Runnable {

    volatile boolean done = false;
    AtomicInteger realA = new AtomicInteger();

    public static void main(String[] args) throws InterruptedException {
        Runnable r =  new UseVolatile1();
        Thread thread1 = new Thread(r);
        Thread thread2 = new Thread(r);
        thread1.start();
        thread2.start();
        thread1.join();
        thread2.join();
        System.out.println(((UseVolatile1) r).done);
        System.out.println(((UseVolatile1) r).realA.get());
    }
    @Override
    public void run() {
        for (int i = 0; i < 10000; i++) {
            setDone();
            realA.incrementAndGet();
        }
    }

    private void setDone() {
      //只对变量进行赋值，且不依赖于以前变量的值是什么
        done = true;
    }
}

package singleton;

/**
 * 描述：     饿汉式（静态常量）（可用）
 */
public class Singleton1 {
	//类在加载的时候就实例化，避免了线程同步问题
    private final static Singleton1 INSTANCE = new Singleton1();

    private Singleton1() {
		//初始化操作
    }
    //发布到外部提供访问
    public static Singleton1 getInstance() {
        return INSTANCE;
    }

}

package singleton;

/**
 * 描述：     饿汉式（静态代码块）（可用）
 */
public class Singleton2 {

    private final static Singleton2 INSTANCE;

    static {
        INSTANCE = new Singleton2();
    }

    private Singleton2() {
    }

    public static Singleton2 getInstance() {
        return INSTANCE;
    }
}

package singleton;

/**
 * 描述：     懒汉式（线程不安全）
 */
public class Singleton3 {

    private static Singleton3 instance;

    private Singleton3() {

    }

    public static Singleton3 getInstance() {
      //如果两个线程同时通过了if条件就会创建多个实例，所以线程不安全
        if (instance == null) {
            instance = new Singleton3();
        }
        return instance;
    }
}

package singleton;

/**
 * 描述：     懒汉式（线程安全）（不推荐）
 */
public class Singleton4 {

    private static Singleton4 instance;

    private Singleton4() {

    }
	//加synchronized关键字虽然线程安全了，但是效率变低了
    public synchronized static Singleton4 getInstance() {
        if (instance == null) {
            instance = new Singleton4();
        }
        return instance;
    }
}

package singleton;

/**
 * 描述：     懒汉式（线程不安全）（不推荐）
 */
public class Singleton5 {

    private static Singleton5 instance;

    private Singleton5() {

    }

    public static Singleton5 getInstance() {
        if (instance == null) {
          //只要多个线程同时进入了if代码块，就不能阻止他们创建实例了，只不过是谁先谁后的问题
            synchronized (Singleton5.class) {
                instance = new Singleton5();
            }
        }
        return instance;
    }
}

package singleton;

/**
 * 描述：     双重检查（推荐面试使用）
 */
public class Singleton6 {

  //加volatile防止重排序，保证可见性
    private volatile static Singleton6 instance;

    private Singleton6() {

    }
	//使用双重锁
    public static Singleton6 getInstance() {
        if (instance == null) {
            synchronized (Singleton6.class) {
                if (instance == null) {
                    instance = new Singleton6();
                }
            }
        }
        return instance;
    }
}