Or is it possible that it will be launched on some other thread? If that's the case, does it spin up a new thread for the function call and joins it to the main thread once the function is done? Or is there something more clever happening? Thanks!
#When calling function using async, does the function run always on the main thread?
fossil coyote
silver crow
Zig won't do multithreading unless you explicitly tell it to
Async effectively generates a state machine - whenever the function suspends, it saves its current state and jumps back to that point when it's resumed
Depending on what you're using async for, the event loop may decide to move suspended functions to other threads, however
But that's not anything to do with the actual language async
This is a decent intro to async in Zig: https://kristoff.it/blog/zig-colorblind-async-await/
acoustic drift
I think calling it a state machine is a bit confusing. IIUC The only state in an async functions that is distinct from a normal function is storing the instruction pointer (and even normal functions kinda do that under the hood)
Async means: create the memory space that a normal function needs, but at a given memory location that is not necessarily on the stack, and allow the function to "put a pin on its action" and temporarily suspend itself. Then keep track of the {memory location, IP} pair as a "future" each time you suspend. Something external would needs to resume it in this case. (This is why I'm dissatisfied with the name "async"). You could write an async function with no suspension points that is basically a really inconvenient to execute normal function.
You're welcome to manually manipulate async functions, and that is useful thing to do, but the language proper doesn't provide you with any conveniences. However, the stdlib does. This is like how zig the language "doesn't have any allocators" but zigs stdlib has more allocators than just about any other LLL
fossil coyote
Thanks @silver crow @acoustic drift! Now it's a lot more clear. So, as I understand if I want multi-threading, the official way to do it is using this - https://github.com/ziglang/zig/blob/master/lib/std/Thread.zig ?
acoustic drift
Yes, use that for simple multithreading, and you don't have to muck around with async
silver crow
I think calling it a state machine is a bit confusing. IIUC The only state in a...
Fair, maybe describing it as a state machine is confusing. That is how it's implemented though I believe
honest inlet
I think calling it a state machine is a bit confusing. IIUC The only state in a...
It's compiled down to a state machine (think "switch case") where each suspension point creates a new "case" in the state machine. The concept of "instruction pointer" doesn't map too well atm because it still uses the OS thread stack + cpu instruction pointer when executing each of it's "case"s.
The name "async" means that the function can execute concurrently/non-synchronously (w.r.t its completion) with other (normal or async) functions; Synchronous functions complete when they return to the caller, which isn't guaranteed to (but can) be the case for async functions.
When interacting with @Frame(func), you're manipulating a (potentially "running") instance of that function rather than the function itself, if that makes any sense. Some stdlib functions like std.event.Loop.runDetached simplify these interactions.
unborn swallow
async code work just like this: #programming-discussion message
acoustic drift
(w.r.t its completion)
Yeah, that's what I don't like about the name. its execution is run exclusively on whatever the thread called it, and as you can see from the head of this thread that fact has already caused confusion, but I don't want to bikeshed too much 😄
oh really, it compiles to a duff's device basically? huh. I still don't like to think of that as a "state machine" tbh I never liked calling async stuff state machines because at some level everything reduces to a state machine. =/
honest inlet
async code work just like this: https://discord.com/channels/605571803288698900/...
this really good example
unborn swallow
yes, if you scroll up to see how long I've been asking for this, due to my own misunderstanding.... 😅
honest inlet
reading through, its kinda unfortunate the builtin/type is called @Frame() cuz it makes you think "stack frame" from stackful coroutines (i.e. fibers)
plain tendon
but it is an activation frame, is it not
silver crow
> (w.r.t its completion)
Yeah, that's what I don't like about the name. its exe...
Async functions can be moved between threads, they don't have to run exclusively on the thread that started them
honest inlet
but it is an activation frame, is it not
What does "activation frame" refer to in this case? All I see online are like a stack with a return address, params/locals, etc. (zig async Frames aren't a stack)
plain tendon
sorry, activation record. the call stack is the designated region of stack-allocated activation records. i don't know why it's never stack record or activation frame, but whatever. it doesn't matter whether it's on the stack or not, a function call is an object.
you might as well call it a frame, because it serves the same purpose of tracking the call's state
honest inlet
yea, but then one could think "stack frame", then infer that it works like that and try to manipulate/inspect it as such
plain tendon
the only other term i can think of is Thunk