Enthuware

Won't the "t.join()" assure that any modifications made by thread t will be seen by the main thread? Won't that assure the value of sum will be 20?

Yes, the join method provides "happen-before" semantics so all updates made by thread t will be seen by the main thread.

But that is not the issue here. The issue is that the update itself is faulty. When thread t tries to update 'sum', it does not acquire the same lock that is used by the main thread. So this update may step on the main thread's update.

HTH,
Paul.

I see you are referring to the last part in the explanation. Yes, you are right. This should be fixed.

Thank you for your feedback.

-Paul.

Actually, I was confused and your response helped clarify my understanding. But improving the explanation would help because I didn't get it the first time.

Thank you.