java - 调用同步方法时线程调用非同步实例方法

Question

public class Common {      
    public synchronized void synchronizedMethod1() {
        System.out.println("synchronizedMethod1 called");
        try {
            Thread.sleep(1000);
            } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("synchronizedMethod1 done");
    }
    public void method1() {
        System.out.println("Method 1 called");
        try {
            Thread.sleep(1000);
            } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("Method 1 done");
    }
}



public class MyThread extends Thread {
    private int id = 0;
    private Common common;

    public MyThread(String name, int no, Common object) {
        super(name);
        common = object;
        id = no;
    }

    public void run() {
        System.out.println("Running Thread" + this.getName());
        try {
            if (id == 0) {
                common.synchronizedMethod1();
                } else {
                common.method1();
            }
            } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        Common c = new Common();
        MyThread t1 = new MyThread("MyThread-1", 0, c);
        MyThread t2 = new MyThread("MyThread-2", 1, c);
        t1.start();
        t2.start();
    }
}

输出:

Running ThreadMyThread-1  
synchronizedMethod1 called  
Running ThreadMyThread-2  
Method 1 called  
synchronizedMethod1 done  
Method 1 done  

我想找到一种方法来阻止method1()在我调用synchronizedMethod1时运行。除非我弄错了，否则所有方法都会被调用，并且 Java 会在运行时期间和之前编译它们，无论它是否同步。

我应该使用 Lock 对象来代替和/或不让 method1() 成为同步方法吗？

Answer 1

I would like to find a way to prevent method1() from running when i called synchronizedMethod1

最简单的方法是使 method1() 也同步。这意味着这两种方法都会导致对它们正在调用的 Common 实例进行锁定。只有一个线程能够调用 synchronizedMethod1() 或 method1()。

Unless I'm mistaken all methods are called and Java compiles them during and before runtime regardless if it's synchronized or not.

我不明白这个问题。您确实不必担心 JVM 的编译或优化阶段。

Should i have used a Lock object instead?

通常认为使方法同步不如使用私有(private)最终锁定对象。锁定对象只是让您的锁定更加细粒度。例如，通过方法锁定，日志消息和其他不需要保护的语句也将被同步。但如果目标是锁定整个方法，那么同步方法就可以了。