Java多线程间同步

1、什么是线程安全

class SellTicketRunnable implements Runnable {

    public int count = 100;

    @Override
    public void run() {
        while (count > 0) {
            try {
                Thread.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            int index = 100 - count + 1;
            System.out.println(Thread.currentThread().getName() + "卖出第" + index + "张票");
            count--;
        }
    }
}

public class JavaSyncDemo {

    public static void main(String[] args) {
        SellTicketRunnable runnable = new SellTicketRunnable();
        Thread sellThread1 = new Thread(runnable);
        Thread sellThread2 = new Thread(runnable);
        sellThread1.start();
        sellThread2.start();
    }
}

2、线程安全问题的解决办法

(1)使用同步代码块
class SellTicketRunnable implements Runnable {

    public int count = 100;

    private Object lock = new Object();

    @Override
    public void run() {
        while (count > 0) {
            try {
                Thread.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            synchronized (lock) {
                if (count > 0) {
                    int index = 100 - count + 1;
                    System.out.println(Thread.currentThread().getName() + "卖出第" + index + "张票");
                    count--;
                }
            }
        }
    }
}

public class JavaSyncDemo {

    public static void main(String[] args) {
        SellTicketRunnable runnable = new SellTicketRunnable();
        Thread sellThread1 = new Thread(runnable);
        Thread sellThread2 = new Thread(runnable);
        sellThread1.start();
        sellThread2.start();
    }
}
(2)使用同步函数
class SellTicketRunnable01 implements Runnable {

    public int count = 100;

    @Override
    public void run() {
        while (count > 0) {
            try {
                Thread.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            this.sale();
        }
    }

    synchronized void sale() {
        if (count > 0) {
            int index = 100 - count + 1;
            System.out.println(Thread.currentThread().getName() + "卖出第" + index + "张票");
            count--;
        }
    }
}

public class JavaSyncDemo01 {

    public static void main(String[] args) {
        SellTicketRunnable01 runnable = new SellTicketRunnable01();
        Thread sellThread1 = new Thread(runnable);
        Thread sellThread2 = new Thread(runnable);
        sellThread1.start();
        sellThread2.start();
    }
}
class SellTicketRunnable02 implements Runnable {

    public static int count = 100;

    @Override
    public void run() {
        while (count > 0) {
            try {
                Thread.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            SellTicketRunnable02.sale();
        }
    }

    static void sale() {
        synchronized (SellTicketRunnable02.class) {
            if (count > 0) {
                int index = 100 - count + 1;
                System.out.println(Thread.currentThread().getName() + "卖出第" + index + "张票");
                count--;
            }
        }
    }
}

public class JavaSyncDemo02 {

    public static void main(String[] args) {
        SellTicketRunnable02 runnable = new SellTicketRunnable02();
        Thread sellThread1 = new Thread(runnable);
        Thread sellThread2 = new Thread(runnable);
        sellThread1.start();
        sellThread2.start();
    }
}
(3)使用lock锁
class SellTicketRunnable03 implements Runnable {

    public int count = 100;

    private Lock lock = new ReentrantLock();

    @Override
    public void run() {
        while (count > 0) {
            try {
                Thread.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            lock.lock();
            if (count > 0) {
                int index = 100 - count + 1;
                System.out.println(Thread.currentThread().getName() + "卖出第" + index + "张票");
                count--;
            }
            lock.unlock();
        }
    }
}

public class JavaSyncDemo03 {

    public static void main(String[] args) {
        SellTicketRunnable03 runnable = new SellTicketRunnable03();
        Thread sellThread1 = new Thread(runnable);
        Thread sellThread2 = new Thread(runnable);
        sellThread1.start();
        sellThread2.start();
    }
}
// lock锁的安全使用方法
class lockDemo {
    Lock lock = new ReentrantLock();
    void demoFun() {
        lock.lock();
        try {
            // 可能出现线程安全的操作
        } finally {
            lock.unlock();
        }
    }
}
(4)使用Java原子类
class SellTicketRunnable04 implements Runnable {

   public AtomicInteger count = new AtomicInteger(100);

   @Override
   public void run() {
       while (true) {
           try {
               Thread.sleep(50);
           } catch (InterruptedException e) {
               e.printStackTrace();
           }
           if (count.get() > 0) {
               int index = 100 - count.getAndDecrement() + 1;
               System.out.println(Thread.currentThread().getName() + "卖出第" + index + "张票");
           }
       }
   }
}

public class JavaSyncDemo04 {

   public static void main(String[] args) {
       SellTicketRunnable04 runnable = new SellTicketRunnable04();
       Thread sellThread1 = new Thread(runnable);
       Thread sellThread2 = new Thread(runnable);
       sellThread1.start();
       sellThread2.start();
   }
}

3、死锁

public class DeadLockDemo01 {

    private static Object lock1 = new Object();
    private static Object lock2 = new Object();

    public static void main(String[] args) {
        new Thread() { //线程1
            public void run() {
                while (true) {
                    synchronized (lock1) {
                        System.out.println(this.getName() + ":获取lock1锁");
                        synchronized (lock2) {
                            System.out.println(this.getName() + ":获取lock2锁");
                        }
                    }
                }
            }
        }.start();

        new Thread() { //线程2
            public void run() {
                while (true) {
                    synchronized (lock2) {
                        System.out.println(this.getName() + ":获取lock2锁");
                        synchronized (lock1) {
                            System.out.println(this.getName() + "::获取lock1锁");
                        }
                    }
                }
            }
        }.start();
    }
}

源码地址

12-15 23:12
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