The Three Fences
Explore the three types of memory fences in modern C++ concurrency—full, acquire, and release fences. Understand how these fences manage operation ordering and synchronization to write correct lock-free programs. Visual examples clarify the subtle interactions between loads and stores around these memory barriers.
We'll cover the following...
Typically, three kinds of fences are used: full fence, acquire fence and release fence. As a reminder, acquire is a load, and release is a store operation. What happens if I place one of the three memory barriers between the four combinations of load and store operations?
-
Full fence: A full fence
std::atomic_thread_fence()between two arbitrary operations prevents the reordering of these operations, but guarantees that it won’t hold for StoreLoad operations. Also, they can be reordered. -
Acquire fence: An acquire fence
std::atomic_thread_fence(std::memory_order_acquire)prevents a ...