Concurrency has always been a complicated aspect of computer science.
With modern hardware increasing not only in speed but also in parallelism, it has become necessary to use concurrency in applications to fully exploit available resources.
This is done using threads, which can be thought of as independently running sub-programs of a larger program, or process. Each thread has its own state – including its stack – and executes its own code, but stacks within the same process can generally share other resources at will.
With even the most simple applications being multi-threaded these days, games are no exception. As such, one can hardly find a modern game engine or framework that does not use parallelism in some form or another.
However, today I do not want to talk about how to move complex systems like physics simulation, AI, pathfinding, or even rendering to different threads – like many games do.
Instead I will look at a specific low-level problem:
Assuming we have a multi-threaded program, how can the different threads communicate, and specifically: how can we make sure that certain code is always run on certain threads.
