Java类中的线程安全:Thread safety in Java class

为什么这个Java类不是线程安全的.

Why is this java class not Thread safe.

class TestClass { private int x; int get() { return x; } void set(int x) { this.x = x; } } 

我读到需要使用 synchronized 关键字来使其线程安全吗?毕竟这些操作不是在原子内部完成的吗?

I read that keyword synchronized is needed to make it thread safe? After all isn't the operations done inside atomic?

问题解答

尽管赋值本身是一个原子操作，但由于硬件和编译器的实现不同，不同的线程可能会看到成员x的不同值.即，由于某种缓存，一个线程进行的修改可能对另一个线程不可见.这通常称为线程可见性问题.

Although the assignment itself is an atomic operation, due to different hardware and compiler implementations, different threads may see different values of the member x. I.e., a modification by one thread may be invisible to the other thread, because of some kind of caching. This is usually called a thread visibility problem.

您可以通过在监视器上进行同步(使用synced关键字或java.util.concurrent锁)，或将x声明为易失性来正确同步代码.

You can synchronize your code properly either by synchronizing on a monitor (using the synchronized keyword or the java.util.concurrent locks), or by declaring x to be volatile.

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