“参考”上的同步或实例
考虑以下代码：
public class Foo {
private static final Object LOCK = new Object();
private Object _lockRef1 = LOCK;
private Object _lockRef2 = LOCK;
private int _indx = 0;
public void dec() {
synchronized(_lockRef1) {
_indx--;
}
}
public void inc() {
synchronized(_lockRef2) {
_indx++;
}
}
}
对 dec() 和 inc() 方法的调用是线程安全的吗？一方面，这些方法在两个不同的实例 _lockRef1 和 _lockRef2 上同步。另一方面，这些实例“指向”同一个对象LOCK...
Consider the following code:
public class Foo {
private static final Object LOCK = new Object();
private Object _lockRef1 = LOCK;
private Object _lockRef2 = LOCK;
private int _indx = 0;
public void dec() {
synchronized(_lockRef1) {
_indx--;
}
}
public void inc() {
synchronized(_lockRef2) {
_indx++;
}
}
}
Is call to methods dec() and inc() threadsafe? On the one hand these methods are synchronized on two different instances _lockRef1 and _lockRef2. On the other hand, these instances "point" on the same object LOCK...
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评论（1）
它们不是“在两个不同的实例上同步” - 仅仅因为您使用两个不同的变量并不意味着有两个不同的实例。您有多个变量，每个变量都具有相同的值 - 对
java.lang.Object的单个实例的引用。所以是的，这是线程安全的。当然，就可读性而言，您不应该编写这样的代码，但假设您只是想了解发生的情况，那就没问题了。
They're not "synchronized on two different instances" - just because you use two different variables doesn't mean there are two different instances. You've got several variables each of which will have the same value - a reference to the single instance of
java.lang.Object.So yes, this is thread-safe. Of course you shouldn't write code like this in terms of readability, but assuming you're just trying to understand what happens, it's fine.