Sequential Consistency

After I've calculated in three different ways the sum of a std::vector I want to draw my conclusions.

Until now, I've used two strategies for the summation of a std::vector. First, I did the whole math in one thread (Single Threaded: Summation of a vector); second multiple threads shared the same variable for the result (Multithreaded: Summation of a vector). In particular, the second strategy was extremely naive. In this post, I will apply my knowledge of both posts. My goal is that the thread will perform their summation as independently from each other as possible and therefore reduce the synchronization overhead. 

There are a lot of issues with the singleton pattern. I'm totally aware of that. But the singleton pattern is an ideal use case for a variable, which has only to be initialized in a thread-safe way. From that point on you can use it without synchronization. So in this post, I discuss different ways to initialize a singleton in a multithreading environment. You get the performance numbers and can reason about your uses cases for the thread-safe initialization of a variable.

With atomic data types, you can tailor your program to your needs and therefore optimize it. But now we are in the domain of the multithreading experts.

The key idea of a std::atomic_thread_fence is, to establish synchronisation and ordering constraints between threads without an atomic operation.

With the acquire-release semantic the memory model gets very thrilling. Because now, we have not to reason about the synchronisation of threads, now we have to reason about the synchronisation of the same atomic in different threads.

I have introduced In the post Sequential Consistency the default memory model. This model, in which all operations in all threads takes place in a global time clock, has a big advantage but also a big disadvantage.

In this post, our tour through the c++ memory model goes one step deeper. Until now, the posts were only about the atomicity of the atomic data types but now we deal with the synchronisation and ordering constraints of the operations.

In addition to booleans, there is atomics for pointers, integrals and user-defined types. The rules for user-defined types are special.

Atomics guarantee two characteristics. On one hand, they are atomic, on the other hand, they provide synchronization and order constraints on the program execution.