On the other hand, not using atomics in heavy multithreaded code is just a recipe for disaster. The problem with shared_ptr is the fact that it uses atomics even in single-threaded code, which is obviously an overkill.
On the other hand imagine the security issues if shared_ptr was not thread-safe - you could just not reliably destroy a shared_ptr in any thread.
If you really know that you're going to get a graph of shared_ptr that do not move of a single thread, you can use boost::local_shared_ptr explicitely.
While it can’t (yet?) be generic over them, it lets you use the non-atomic Rc in thread-bound structures and know this is never going to be shared between threads, whereas the more expensive Arc can have handles be moved from one thread to an other.
[1] https://github.com/duneroadrunner/SaferCPlusPlus#reference-c...
[2] https://github.com/duneroadrunner/SaferCPlusPlus#tasyncshare...