[spinningslate]

thank you for writing this.

I cut my teeth on OS/2 in the early 90s, where using threads and processes to handle concurrent tasks was the recommended programming model. It was well-supported by the OS, with a comprehensive API for process/thread creation, deletion and inter-task communication. It was a very clear mental model: put each sequential sequence of operations in its own process/thread, and let the operating system deal with scheduling - including pausing tasks that were blocked on I/O.

My next encounter was Windows 3, with its event loop and cooperative multi-tasking. Whilst the new model was interesting, I was perplexed by needing to interleave my domain code with manual decisions on scheduling. It felt haphazard and unsatisfactory that the OS didn't handle scheduling for me. It made me appreciate more the benefits of OS-provided pre-emptive multi-tasking.

The contrast in models was stark. It seemed obvious that pre-emptive multi-tasking was so obviously better. And so it proved: NT bestowed it on Windows, and NeXT did the same for Mac.

Which brings us to today. I feel like I'm going through groundhog day with the renaissance of cooperative multi-tasking: promises, async/await and such. There's another topic today [0] that illustrates the challenges of attempting to performs actions concurrently in javascript. It brought back all the perplexion and haphazard scheduling decisions from my Windows 3 days.

As you note:

> Of course, context switching between different tasks is not free, and event loops have frequently been able to provide higher efficiency.

This is indeed true: having an OS or language runtime manage scheduling does incur an overhead. And, indeed, there are benchmarks [1] that can be interpreted as illustrating the performance benefits of cooperative over pre-emptive multitasking.

That may be true in isolation, but it inevitably places scheduling burden back on the application developer. Concurrent sequences of application domain operations - with the OS/runtime scheduling them - seems like a better division of responsibility.

[0]: https://news.ycombinator.com/item?id=42592224

[1]: https://hez2010.github.io/async-runtimes-benchmarks-2024/tak...

[pjmlp]

Did you ever used SOM?

To this day it still seems it had a much better approach to components development and related tooling, than even COM reboot as WinRT offers.

[spinningslate]

Yes! Fond memories. I put it firmly in the Betamax category: superior technology that lost out for political/marketing reasons.

[homarp]

for those curious about SOM OS/2 Technical Library: System Object Model Guide and Reference

https://archive.org/details/os2-2.0-som-1991

[jerf]

What makes me angriest about the current async propaganda... and I use the term deliberately to distinguish it from calm discussions about relative engineering tradeoffs, which is a different discussion... is the idea that it started with Node.

Somehow we collectively took all the incredible experience with cooperative multitasking gathered over literally decades prior to Node and just chucked it in the trash can and had to start over at Day Zero re-learning how to use it.

This is particularly pernicious because the major issue with async is that it scales more poorly than threads, due to the increasing design complexity and the ever-increasing chances that the various implicit requirements that each async task has for the behavior of other tasks in the system will conflict with each other. You have to build systems of a certain size before it reveals its true colors. By then it's too late to change those systems.

[jandrewrogers]

I would frame it a bit differently. Async scales very elegantly if and only if your entire software stack is purpose-built for async.

The mistake most people are making these days is mixing paradigms within the same thread of execution, sprinkling async throughout explicitly or implicitly synchronous architectures. There are deep architectural conflicts between synchronous and asynchronous designs, and trying to use both at the same time in the same thread is a recipe for complicated code that never quite works right.

If you are going to use async, you have to commit to it with everything that entails if you want it to work well, but most developers don't want to do that.

[sickblastoise]

This is actually a major issue in the LLM wrapper space. Building things like agents (which I think are insanely overhyped and I am so out on but won’t elaborate on), usually in Python, where you are making requests that might take 1-5 seconds to complete, with dependencies between responses, you basically need to have expert level async knowledge to build anything interesting. For example, say you want two agents talking to eachother and “thinking” independently in the same single threaded Python process. You need to write your code in such a way that one agent thinking (making a multi second call to an llm) does not block the other from thinking, but at the same time when the agents talk to each other they shouldn’t talk over eachother. Now imagine you have n number of these agents in the same program, say behind an async endpoint on a FastAPI server. It gets complicated quick.

[mpweiher]

It's also unnecessary for virtually all actual systems today.

The systems that can potentially benefit from async/await are a tiny subset of what we build. The rest just don't even have the problem that async/await purports to solve, never mind if it actually manages to solve it.