Java：有正确的方法来使用静态volatile变量吗？ [英] Java: Is there a right way to use static volatile variables?

问题描述

我想有一个标志，可以访问从不同的线程读/写，没有任何脏值的问题。是否足以使其变为静态变量？

I want to have a flag that could be accessible to read/write from different threads without any problem of dirty values. Is it enough to make it static volatile?

static volatile boolean flag;

推荐答案

不，这是不够的，如果你需要一个动作像这样：

No, this is not enough if you need an action like this:

volatile int v = 0;

Thread 1:
v++;

Thread 2:
v--;

理想情况下，当您执行上述代码时，您希望v = 0，但这是真正发生的事情复合动作）：

Ideally you want v=0 when you execute the above code, but this is what is really happening (a composite action):

Thread 1:
r1 = v;
r2 = r1 + 1;
v = r2;

Thread 2:
r3 = v;
r4 = r3 - 1;
v = r4;

这两个线程分别给出值1和-1。资料来源：挥发性不意味着原子！

And both the threads will give values of 1 and -1 respectively. Source: Volatile Does Not Mean Atomic!

如果你需要在多线程场景中保证一致的结果，你应该使用Java中的Atomic类，正如@ Eng.Fouad指出的那样。

If you need guaranteed consistent result in a mulithreaded scenario, you should be using Atomic classes in Java as @Eng.Fouad pointed out.

在布尔值的情况下，compare-and-set将比使用volatile有利于AtomicBoolean类。

In the case of a boolean too, compare-and-set will be helpful from AtomicBoolean class than using volatile.

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