Synchronized Methods

Question

If I have a synchronized public method and a private method:

public synchronized void doSomething() {
    doSomethingElse()
}

private void doSomethingElse() {
}

Do I need to synchronize the private method?

Answer 1

Any methods called from a synchronized method (or from within a synchronized block) are run while still synchronized. You don't need to separately synchronize the private method if it is only called from synchronized methods.

Answer 2

This is the intent of the @GuardedBy annotation. If you expect that a lock must be held when calling that method, annotate it with that and the name of the lock (in the example it would be:

@GuardedBy("this") private void doSomethingElse() {…}

Then you can check that the invariant is true with FindBugs.

You can also use the other net.jcip.annotations for describing the thread-safety or lack of it and have FindBugs validate these assumptions too. Of course, the book needs a plug as well.