I read that as "green threads". But it could be anything just short of a thread maybe even futures and promises.
Just about any thread that isn't a full-on proper thread is not ideal for general purpose game development. There are a lot of thread implementations for various user interfaces that have a goal of minimizing latency or maximizing CPU utilization. But if you are in a latency sensitive environment like a game and you're highly likely to be pushing the CPU to 100% you often need real threads not something like them.
Coroutines have their place in game development too, but they're not (in my experience) used as a thread replacement. They are used to manage complex flow control. Similarly, I have seen green threads and event loops used to manage the user interface or Futures and Promises to manage certain IO in a game but not the rest of the general game work scheduling.
Just about any thread that isn't a full-on proper thread is not ideal for general purpose game development. There are a lot of thread implementations for various user interfaces that have a goal of minimizing latency or maximizing CPU utilization. But if you are in a latency sensitive environment like a game and you're highly likely to be pushing the CPU to 100% you often need real threads not something like them.
Coroutines have their place in game development too, but they're not (in my experience) used as a thread replacement. They are used to manage complex flow control. Similarly, I have seen green threads and event loops used to manage the user interface or Futures and Promises to manage certain IO in a game but not the rest of the general game work scheduling.