java - java中静态变量的线程安全

Question

我的问题与静态变量的线程安全有关。

Class A{
private static int test=0;
public static void synchronized  m1(){
    test=test+1;
}
public void synchronized  m2(){
   test=test+1;
}

}

If two threads, t1 having static lock and t2 having object lock, can continue simultaneously, then how will state test of class A will be thread safe?

可能是，我错过了一些非常基本的东西，但不确定它是如何工作的。

Based on below answers, I get the impression that if such states have to be made thread safe, then either both locks should be held by a thread which is updating this state, or make sure it is being accessed by either only static methods or only non-static methods. right?

Answer 1

这不是线程安全的。这些方法使用不同的监视对象:静态方法使用类，实例方法使用对象实例进行同步。您可以通过以下方式使实例方法使用该类作为监视对象:

synchronized (A.class) {
...

如果你需要的话。我会考虑将这两种方法设为静态，除非您需要访问实例变量。