Java基础——Synchronized

羊羽shine

发布于 2019-05-28 13:33:59

2870

发布于 2019-05-28 13:33:59

文章被收录于专栏：Golang开发Golang开发

作用

能够保证在同一个时刻最多只有一个线程执行该代码，以达到保证并发安全的效果。

资源竞争

造成数据不安全

public class SumThread implements Runnable {
    private static int count = 0;
    public void run() {
        for(int i =0;i<10000;i++){
            count++;
        }
    }
       public static void main(String[] args)  {
        SumThread thread = new SumThread();
        Thread t1 = new Thread(thread);
        Thread t2= new Thread(thread);
        t1.start();
        t2.start();
        System.out.println(count);
    }
}

对象锁

方法锁 synchronized修饰普通方法，不可以是静态方法，锁对象默认是this

public class SynchronizedThread implements Runnable {
    public void run() {
        executeThread();
    }
    private synchronized void executeThread(){
        System.out.println(Thread.currentThread().getName()+" start");
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(Thread.currentThread().getName()+" finish");
    }
}

同步代码锁块 需要指定锁对象

public class SynchronizedThread implements Runnable {
    public void run() {
        synchronized (this){
            System.out.println(Thread.currentThread().getName()+" start");
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName()+" finish");
        }
    }
    public static void main(String[] args)  {
        SynchronizedThread thread = new SynchronizedThread();
        Thread t1 = new Thread(thread);
        Thread t2= new Thread(thread);
        t1.start();
        t2.start();
    }
}

类锁

Java类可能有很多个对象，但是只有1个Class对象，类锁只能在同一个时刻被一个对象所拥有。

public class SynchronizedThread implements Runnable {
    public void run() {
        synchronized (SynchronizedThread.class){
            System.out.println(Thread.currentThread().getName()+" start");
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName()+" finish");
        }
    }
}