Java methods thread safe

Question

I have a scenario, searched quite a bit, but did not get satisfactory answer.

There is a service class, WebserviceInvokerService,

class WebserviceInvokerService {
    @Override
    public void synchronized callBackFun() {...}
}

callBackFun ==> is the function which gets called when an event (some event) occurs.

In callBackFun I check DB and accordingly do a service call (no instance members of the class are involved in this business).

I have made callBackFun synchronized. There is a possibility that, multiple instances of WebserviceInvokerService will be created and callBackFun will be called on those objects.

I want callBackFun to be called "synchronously" across the objects. So will the "synchronized" for callBackFun will make any sense in such scenario.

Answer 1

If you java multiple instances WebserviceInvokerServices the methods will be synchronized in each of these instances, but not across the instances.

What you might be looking for is a Lock.

You can try this:

private final static Lock lock = new ReentrantLock();

@Override
public void callBackFun() {
    lock.lock();
    try {
        // Do things here
    } finally {
        lock.unlock();
    }
}

EDIT: Added the final keyword as mentioned by @Wyzard