FoundationDB's Flow – Bringing Actor-Based Concurrency to C++11

Post by pjmlp » Sat, Jul 04, 2026, 5:40 AM UTC

whizzter wrote: post #21

menaerus wrote: post #12

Earlier quoted context omitted.

> Nah, coroutines/async/etc often lives in various threads (ie, the workers can schedule one of them on different threads during the lifetime and they live concurrently), so you still have all the issues of threading (+ new ones since things like thread-local variables aren't reliable if an async/coroutines moves threads between calls). In cooperative scheduling how is it possible to have two coroutines running concu…

You're thinking of older early coroutines or in singlethreaded runtimes (JS). It's M:N threading, most logical threads/tasks are more lightweight than full OS threads, the logical ones should preferably behave cooperatively but they can be scheduled onto any number of real worker threads (usually these systems picks something like 2x worker threads compared to real CPU/Core count to manage some codepaths not being as…

Post by d4ng » Sat, Jul 04, 2026, 4:32 PM UTC

mgaunard wrote: post #32

d4ng wrote: post #29

Earlier quoted context omitted.

The actor itself can be said to be waiting. When it yields, the thread is then able to run another actor which was waiting on a message, and which then has a message on the queue.

That sounds like a misunderstanding of how the actor model works. An actor doesn't wait. It's an event-driven system, it doesn't get to own and decide when messages get fed to it.

Post by d4ng » Sun, Jul 05, 2026, 1:40 AM UTC

mgaunard wrote: post #34

d4ng wrote: post #33

Earlier quoted context omitted.

Are there any actor system implementations that you know of that work differently?

Well in mine for example, threads are pinned to a core and always spin, and actors are pinned to a given thread (you can have an arbitrary number of actors per thread, they're just objects), so "waiting" is certainly not something you'd use to describe the setup in any capacity.

Post by whizzter » Mon, Jul 06, 2026, 1:30 PM UTC

pjmlp wrote: post #31

whizzter wrote: post #21

Earlier quoted context omitted.

You're thinking of older early coroutines or in singlethreaded runtimes (JS). It's M:N threading, most logical threads/tasks are more lightweight than full OS threads, the logical ones should preferably behave cooperatively but they can be scheduled onto any number of real worker threads (usually these systems picks something like 2x worker threads compared to real CPU/Core count to manage some codepaths not being as…

C++20 co-routines model is based on .NET ones, as the original model was proposed by Microsoft and inspired on WinRT work. If you know how to create asyncable types on .NET, the magic methods expected by C++ compiler will feel familiar.