Multithreading: do I need protect my variable in read-only method?

Question

I have few questions about using lock to protect my shared data structure. I am using C/C++/ObjC/Objc++

For example I have a counter class that used in multi-thread

Answer 1

Yes, you would need to lock the read as well in this case.

There are several alternatives -- a lock is quite heavy here. Atomic operations are the most obvious (lock-free). There are also other approaches to locking in this design -- the read write lock is one example.