Comment by bluGill

Shared data is hard no matter what you do. Parallelism and shared data do not mix. STM makes some things easier, but you still will run into problems if you have a lot of it. You must design your code such that you spend a lot of CPU cycles doing single thread no shared data calculations between every place where you need to share data. If you can't do that you can't do parallelism.

When there are only a few places where data needs to be shared a mutexs works since you put your best programmer on maintaining just that code and with only a few places they can figure out it. You can also make a variable atomic, which sometimes works better than a mutex and sometimes worse. You can use STM. However no matter what you use the reality of synchronizing between cores means you can't do any of the above "very often".