What's a "control block"

Question

While reading the boost::coroutine documentation, I came accross the term control block :

The solution is that each coroutine has its own stack and control-block

While the notion of a stack is fairlly familiar, I've never encountered the term control block before. The following image may have provided some contextual (no pun intended) understanding of what a control block is

Since I can't google my way to a better explanation (the provided link to boost context only made things more obscure), could anyone provide a solid definition and explain the workings of a control block?

thanks

Answer 1

The term dates back to the Process Control Block from IIRC CP/M, at least 4 decades. It's the block of data which describes a running context. Later on, threads got Thread Control Blocks Here the need for state meant a similar data structure, so the name Control Block makes sense. The only oddity is that usually these Control Blocks are OS structures, but boost coroutines aren't OS managed.