两个不同的类A和B在各自的线程上调用相同类实例C的方法

Question

So I've got a simple Server class that creates an instance of a Listener class for every connection made to the "server". The Listeners run on their own thread.

I get that there might be a concurrency control problem when invoking methods on the Server class that alter files/variables. But what happens if 2 Listeners try to invoke a method that eg only returns some information about the server status? Can the same Server instance handle 2 calls at the same time? Or will one of the listeners have to wait till the server is done executing the method of the first caller?

Thanks for any help you guys might be able to provide!

Answer 1

If the method is not synchronized, the server can handle the two calls concurrently.

But if they ask for status, this means that the status changes over time. And if it changes over time, then all accesses, read and write, to this status should be done in a synchronized way. Otherwise, the listener threads could see an obsolete value of the status.

So the method should be synchronized, or the status should be an AtomicXxx value, or it should be volatile. The best, and correct solution is hard to give without seeing the code and knowing how the status is read and modified.

Answer 2

对于类似的事情，我想它不会经常改变，我会考虑使用ReadWriteLock-因此，大多数情况下，您可以让多个线程同时读取状态，并且只在需要更新值时才阻塞它们。