TC39 Async Context
2022-12-13
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15:47
<littledan>
There's some related discussion on Mastodon! https://hachyderm.io/@develwithoutacause@techhub.social/109488473692344107
15:47
<littledan>
Doug, who started the thread and works on Angular, might be thinking about their use of zone.js
15:48
<littledan>
Does anyone want to get in touch with Doug and Minko for a review of AsyncContext from Angular's perspective?
15:49
<littledan>
Misko Hevery (of Angular fame) did a quick review of the AsyncContext API. He told me it seemed good to focus on just one aspect, but that Angular would still miss the ability to run a callback "when the microtask queue becomes empty" (a concept which isn't very composition-friendly, but which Angular needs to decide when to render to the DOM)
16:08
<Justin Ridgewell>
That sounds like they need a scheduling API
16:10
<littledan>
I think they need an API analogous to requestAnimationFrame but that runs a little earlier
16:11
<littledan>
anyway they currently implement this by patching promises and also transpiling async/await such that it uses those promises. This lets them implement both AsyncContext and a mechanism to count how many outstanding microtask queue items there are
16:11
<littledan>
so AsyncContext alone will not solve the whole problem that they are patching promises for. Anyway, I agree with Misko that we shouldn't attempt to solve their whole problem
17:23
<Kris Kowal>
Misko Hevery (of Angular fame) did a quick review of the AsyncContext API. He told me it seemed good to focus on just one aspect, but that Angular would still miss the ability to run a callback "when the microtask queue becomes empty" (a concept which isn't very composition-friendly, but which Angular needs to decide when to render to the DOM)
At Agoric, we have historically drained the microtask queue in two different ways. You can approximate it with setImmediate, since it enqueues an event on the I/O queue. But, now we use a privileged API provided by XS that lets us dispatch an event and wait for the event loop to quiesce.
17:25
<Kris Kowal>
The latter we invoke from outside the execution context. Doing the same from inside an execution context is a bit of an ouroboros, or as littledan put it, doesn’t compose well.
17:25
<littledan>
At Agoric, we have historically drained the microtask queue in two different ways. You can approximate it with setImmediate, since it enqueues an event on the I/O queue. But, now we use a privileged API provided by XS that lets us dispatch an event and wait for the event loop to quiesce.
Yeah, this sort of solution sounds great to me; I hope Angular can find a similar solution for itself. (Or it might go "zoneless" but they have been talking about that since 2017...)