What are the differences between memory ordering models?

What are the differences between memory ordering models?

Memory ordering models define how operations are ordered in a multi-threaded environment. The main types include sequential consistency, total store order, and relaxed memory models. Each has different guarantees about the visibility of operations across threads.

Can you explain sequential consistency in more detail?

Sequential consistency ensures that the result of execution is the same as if all operations were executed in some sequential order. This means that all threads see the same order of operations, which simplifies reasoning about program behavior.

What about total store order?

Total store order (TSO) allows for some reordering of loads and stores, but it ensures that all stores from a single thread appear in order to all other threads. This model is commonly used in x86 architectures.

How do relaxed memory models differ from these?

Relaxed memory models allow for more flexibility in the ordering of operations, which can improve performance. However, they require programmers to use synchronization mechanisms carefully to avoid unexpected behaviors.