AtomicSharedPtr | Free implementation of std : : atomic std : : shared_ptr

First, a sidenote. std::atomic> gives atomic access to the pointer, and provides no synchronization whatsoever for the T. That's super important to note here. And your code shows that you're trying to synchronize the T, not the pointer, so the atomic is not doing what you think it is. In order to use std::atomic>, you must treat the pointed-at T as const.

There's two ways to handle read-modify-write with arbitrary data in a thread safe way. The first is, obviously, to use locks. This is usually faster to execute and due to its simplicity, usually less buggy, and is therefore highly suggested. If you really want to do this with atomic operations, it's difficult, and executes slower.

It usually looks something like this, where you make a deep copy of the pointed-at data, mutate the copy, and then attempt to replace the old data with the new data. If someone else has changed the data in the meantime, you throw it all away and start the whole mutation over.