线程安全

数据竞争

车票售卖

package cn.bx.thread;
class TicketWindow implements Runnable {
    private int count = 100;
    public void run() {
        while (true) {
                if (count > 0) {
                    try {
                        Thread.sleep(10);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(Thread.currentThread().getName() + "售出车票，剩余车票:" + (--count));
                } else {
                    break;
                }
        }
    }
}
public class Ticket {
    public static void main(String[] args) {
        TicketWindow ticketWindow = new TicketWindow();
        Thread one = new Thread(ticketWindow);
        Thread two = new Thread(ticketWindow);
        Thread three = new Thread(ticketWindow);
        one.setName("1号窗口");
        two.setName("2号窗口");
        three.setName("3号窗口");
        one.start();
        two.start();
        three.start();
    }
}

会出现数据竞争

1号窗口售出车票，剩余车票:0
2号窗口售出车票，剩余车票:-1
3号窗口售出车票，剩余车票:-2

synchronized

class TicketWindow implements Runnable {
    private int count = 100;
    public void run() {
        while (true) {
            synchronized (this) {
                if (count > 0) {
                    try {
                        Thread.sleep(10);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(Thread.currentThread().getName() + "售出车票，剩余车票:" + (--count));
                } else {
                    break;
                }
            }
        }
    }
}

单例模式

package cn.bx.thread;
class Singleton {
    private static  Singleton instance = null;
    private Singleton(){}
    public  static Singleton getInstance(){
        if (instance==null){
            synchronized (Singleton.class){
                if (instance==null){
                    instance = new Singleton();
                }
            }
        }
        return instance;
    }
}
public class SingletonNote {
    public static void main(String[] args) {
        Singleton foo = Singleton.getInstance();
        Singleton bar = Singleton.getInstance();
        System.out.println(foo ==bar);
    }
}

Lock

class A {
    private final ReentrantLock lock = new ReenTrantLock();
    public void m() {
        lock.lock();
        try {
//保证线程安全的代码;
        } finally {
        }
    }
}