[hathawsh]

Exactly. The way I think about it, the "async" keyword transforms function code so that local variables are no longer bound to the stack, making it possible to pause function execution (using "await") and resume it at an arbitrary time. Performing that transformation manually is a fair amount of work and it's prone to errors, but that's what we did when we wrote cooperatively multitasked code.

[nottorp]

> when we wrote cooperatively multitasked code

That's my point, we still do that. And based on your phrasing we're forgetting it :)

[hathawsh]

Sure, that's a good way to look at it. Another way to look at it: because the process of transforming code for cooperative multitasking is now much cleaner and simpler, it's fine to use new words to describe what to do and how to do it.

[kragen]

cooperative multitasking, as i use the term, keeps you from having to transform your code. it maintains a separate stack per task, just like preemptive multitasking. so async/await isn't cooperative multitasking, though it can achieve similar goals

possibly you are using the terms in subtly different ways so it appears that we disagree when we do not

[nottorp]

Cooperative multitasking is "The illusion of simultaneously executing code paths by having said code paths pass control to each other fast enough."

If the OS forcefully switches control it's preemptive.

[kragen]

that definition is different from the definition i'm using; it covers both what i'm calling 'cooperative multitasking' and things like async/await, the npm event handler model, and python/clu iterators

in the mac os 8 documentation, explaining how mac os 8 only has 'cooperative multitasking', the term is defined in the way i'm using it (https://developer.apple.com/library/archive/documentation/Ca...):

> In programming, a task is simply an independent execution path. On a computer, the system software can handle multiple tasks, which may be applications or even smaller units of execution. For example, the system may execute multiple applications, and each application may have independently executing tasks within it. Each such task has its own stack and register set.

> Multitasking may be either cooperative or preemptive. Cooperative multitasking requires that each task voluntarily give up control so that other tasks can execute. (...)

> The Mac OS 8 operating system implements cooperative multitasking between applications. The Process Manager can keep track of the actions of several applications. However, each application must voluntarily yield its processor time in order for another application to gain it. An application does so by calling WaitNextEvent, which cedes control of the processor until an event occurs that requires the application’s attention.

that is, this requirement that each task have its own stack is not just something i made up; it's been part of common usage for decades, at least in some communities. the particular relevant distinction here is that, because each task has its own stack (or equivalent in something like scheme), multitasking doesn't require restructuring your code, because calling a normal function can yield the cpu. in the specific case of macos this was necessary so that switcher/multifinder/process-manager could multitask mac apps written for previous versions of macos that didn't have multitasking

what term would you propose for what i'm calling 'cooperative multitasking', like forth and mac os 8 and windows 3.1 (https://softwareengineering.stackexchange.com/questions/3507... https://retrocomputing.stackexchange.com/questions/791/how-d...)? this terminology is not absolutely standardized, and i'd be happy to use different terminology in order to be able to communicate productively

also could you please answer my request for clarification in https://news.ycombinator.com/item?id=38861074

[nottorp]

> it covers both what i'm calling 'cooperative multitasking' and things like async/await, the npm event handler model, and python/clu iterators

Those are implementation details. What's actually happening in all cases is my definition.

> also could you please answer my request for clarification in

Yes, your examples or the 5 million other implementations of event loops. You forgot to add gtk's for example :)

> in the mac os 8 documentation

... and I see no mention of stacks on Wikipedia:

https://en.wikipedia.org/wiki/Cooperative_multitasking

Which lumps in both the explicit event loop style and the syntactic sugar that got added later.

We could throw definitions around till kingdom come like this. And it's not the exact definition that's my problem.