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jyn
12 comments
rain 🌦️

@jyn oh I'm referring to futures vs tasks -- futures need to be driven externally while tasks are driven by the executor to completion

4 September at 2:51 | Open on hachyderm.io
jyn

@rain ahh got it

hmm i think i haven't heard that distinction using those words, i know rust has the first model and javascript has the latter but i've always considered "future" and "task" synonymous until now

4 September at 2:52 | Open on tech.lgbt
rain 🌦️

@jyn Rust actually has both models! futures are async blocks or manual impls, tasks are futures given to the executor to run

4 September at 2:53 | Open on hachyderm.io
rain 🌦️

@jyn And yes JS only has the latter model -- every JS async call is a tokio::spawn basically

4 September at 2:53 | Open on hachyderm.io
rain 🌦️

@jyn (When I first started writing async Rust, with futures 0.1, I didn't understand the difference until almost a year in lol...

the first time I used an executor, it was to trampoline a recursive traversal of an arbitrary-depth graph, not to run pieces of code in parallel

4 September at 2:57 | Open on hachyderm.io
Predrag Gruevski

@rain @jyn interesting, why was an executor trampoline necessary when recursing across an arbitrary-depth graph?

4 September at 3:00 | Open on hachyderm.io
rain 🌦️

@predrag @jyn Oh well, if you just await on a (boxed) child future you'll end up with an arbitrary-depth pointer stack -- so you need to go up to the top every so often

(We're talking 10 million+ depth)

4 September at 3:05 | Open on hachyderm.io
Predrag Gruevski replied to rain

@rain @jyn I figured it was something like that, but I haven't used nearly enough async Rust yet to be able to construct the precise counterexample in my head.

Thanks!

4 September at 3:06 | Open on hachyderm.io
rain 🌦️ replied to Predrag

@predrag @jyn let's say you're traversing a Merkle linked list (in this case a chain of source control commits) to fold over them recursively -- if you just create a child future with the recursive call then await it, your task stack will grow in an unbounded fashion. If you spawn a new task for each node instead, this isn't an issue

4 September at 3:09 | Open on hachyderm.io
Predrag Gruevski replied to rain

@rain @jyn how does one recover the results of each task in this case?

mpsc shenanigans? Or something more elegant?

4 September at 3:11 | Open on hachyderm.io
rain 🌦️ replied to Predrag
rain 🌦️ replied to rain

@predrag @jyn Oneshot channels are kind of the bread and butter of async communication, because they're equivalent to calling a function and getting a return value back

4 September at 3:43 | Open on hachyderm.io
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