CareerCup

It isn't clear from your description what happened to the application, and why we'd assume that it happened in this section of the code.

Assuming that the thread lock was not released, I'd guess that Func has raised an exception. It is usually best to envelope mutex lock and release with a try\except mechanism, making sure that the lock is released even if an exception is raised. (Allowing you to clean up before shutting down)

And about part 3 -
I'd put another print after Func, to check whether the error was inside Func or not. And if it was, add more prints inside Func recursively until I find the specific line which generated the exception.

might be some problem inside function and it is not able to handle exception occurs inside the fun

The application perhaps is in a deadlock. Lock wasn't released because of an exception in func(). Another thread waiting for the unreleased lock is kept in waiting state forever.

To avoid this situation, surround func() in a try, catch. Release the lock when an exception is thrown.

Actually CalledFunc() should be present in a try-catch-finally block. If you are using your own lock objects, they must be explicitly released in the finally block.

Func() might have called CalledFunc() again recursively. Which caused a case for need of re-entrant lock. So in this case same thread is waiting for the lock which was already acquired by it and hence deadlock.

Func() might have called CalledFunc() again recursively. Which caused a case for need of re-entrant lock. So in this case same thread is waiting for the lock which was already acquired by it and hence deadlock.

So using re-entrant protection lock might help if that's the issue.

1) Program stopped working. so it might have gone into deadlock. if it is c/C++ generate core file using gcore <processid> / pstack to see current stack trace of threads and who is holding the lock.

2) Inside func(), there can be code to obtain the same lock which is already locked by the calling thread or some other locks which has been taken in different order.

3) If execption is thrown, release the lock that is held in catch block