Synchronized Block within Synchronized Method

Question

I\'m looking at some code in a third party library that contains a synchronized method, and within this method there is a synchronized block that locks on an instance variab

Answer 1

When you say "synchronized method locks on the entire object", that's not true. Using synchronized only means that threads have to acquire that lock before they can enter the methods or blocks marked as synchronized that use that lock. The default object used as a lock for synchronized on instance methods is this. The default is this.getClass() if you put synchronized on a static method, or you can specify the object to use as a lock. Using synchronized doesn't do anything other than that to make instance fields inaccessible.

You can write a class where some methods or blocks are protected by one lock, some are protected by another lock, and for others you need both locks. Make sure you acquire the locks in the same order or you can cause a deadlock.