| 00:01 | <Justin Ridgewell> | Because it uses EnqueueMicrotask, which doesn't preserve the context: https://source.chromium.org/chromium/chromium/src/+/main:v8/src/builtins/promise-resolve.tq;l=189;drc=4c61bb3131b7951ed2ed896b4df6110b1e5c072f |
| 01:36 | <littledan> | Let me know if I should write this; I am happy to do so but don’t have Edit access |
| 02:13 | <Justin Ridgewell> | Send me your email, and I’ll give you edit access |
| 02:14 | <Justin Ridgewell> | Or send me notes, and I’ll add them to the deck |
| 02:14 | <Justin Ridgewell> | I don’t really know anything about open telemetry |
| 02:18 | <Chengzhong Wu> | Sorry I was out yesterday and now I'm back on work. Catching up with the long discussions. |
| 02:29 | <littledan> | My email for slides is littledan@chromium.org |
| 02:30 | <littledan> | Will post outline of presentation edits here in the coming hours |
| 02:31 | <littledan> | So the question then is, is this fixable with V8 changes? |
| 02:35 | <littledan> | My notes since legendecas was gone:
|
| 02:55 | <James M Snell> | I'd add that v8's API will definitely need to be expanded to EnqueueMicrotask in order for thenables to be supported |
| 02:55 | <James M Snell> | (And for queueMicrotask) |
| 03:02 | <Justin Ridgewell> | Yes, this is due to V8 not fully implementing the host hooks |
| 03:02 | <Justin Ridgewell> | All jobs should carry the [[HostDefined]] slot (what they're calling continuation_preserved_embedder_data), but currently only Promise jobs do it |
| 03:46 | <littledan> | queueMicrotask is in the same logical bucket as setTimeout though, isn’t it? Like, everything needs plumbing |
| 03:47 | <littledan> | But thenables would need built in support otoh |
| 03:48 | <Justin Ridgewell> | Kinda, and no |
| 03:48 | <littledan> | Note that the job system in the JS spec has historically contained certain… standing disagreements between layers |
| 03:48 | <littledan> | The V8 API can do whatever it wants; there is no obligation to match the JS spec |
| 03:49 | <littledan> | Anyway this is to say that I don’t know what “all jobs” means |
| 03:49 | <Justin Ridgewell> | queueMicrotask seems to be the equivalent of a quick job, and they're not properly implementing the hooks for jobs |
| 03:49 | <Justin Ridgewell> | setTimeout might be a job, but I have no idea how it's implemented |
| 03:49 | <littledan> | Do you mean literally the function queueMicrotask, or the V8 API used to implement it? |
| 03:49 | <Justin Ridgewell> | Sorry, I meant queueMicrotask |
| 03:49 | <Justin Ridgewell> | No, EnqueueMicrotask |
| 03:50 | <Justin Ridgewell> | Ugh |
| 03:50 | <littledan> | Oh! ok, the V8 API |
| 03:50 | <littledan> | Now I understand better |
| 03:50 | <littledan> | Yeah I can imagine that we need something there |
| 03:51 | <Justin Ridgewell> | Specifically, steps 13-15 of https://tc39.es/ecma262/multipage/control-abstraction-objects.html#sec-promise-resolve-functions are all jobs code, but they're implemented in V8 as a single EnqueueMicrotask |
| 03:52 | <Chengzhong Wu> | Node.js tracks queueMicrotask with the async resource API: https://github.com/nodejs/node/blob/main/lib/internal/process/task_queues.js#L152 |
| 03:52 | <Chengzhong Wu> | similar to setTimeout |
| 03:52 | <Justin Ridgewell> | Thenables shouldn't need specific support, the spec for them would work if V8 had fully implemented the job hooks |
| 03:54 | <littledan> | Please, let’s make our arguments on the basis of what is useful, not on what someone is expected to do based on how the spec is written. The latter is a weaker argument and less relevant. |
| 03:55 | <littledan> | Node.js tracks |
| 03:56 | <littledan> | This is a place where we should learn from Yoav’s implementation experience |
| 03:57 | <Justin Ridgewell> |
Because it prevents an embedder from implementing a feature specifically designed in the spec, I do think it's a problem. |
| 04:03 | <littledan> | I think if you make an argument on this basis, you will get a flat no. It just isn’t the contract that engines sign up for. |
| 04:04 | <littledan> | If we make an argument based on case by case utility, it will be more effective |
| 04:05 | <littledan> | Part of this is, there are some things about the interface Ecma-262 provides which are very wacky and bad; engines don’t actually want to sign up for implementing all of that |
| 04:06 | <littledan> | So you are asking for more than you need if you say that they should do everything corresponding to that interface |
| 04:07 | <littledan> | Eg it is fine that there is no actual imperative V8 API to get the time zone and that it does things via libc or ICU |
| 04:08 | <Justin Ridgewell> | I think we're getting off on a tangent. |
| 04:09 | <Justin Ridgewell> | The spec will have explicit requirements for AsyncContext, and when that exists, the hooks won't really matter |
| 04:09 | <Justin Ridgewell> | They only matter now because we're trying to shoehorn in AsyncContext |
| 04:09 | <Justin Ridgewell> | It's unfortunate it doesn't work properly |
| 04:09 | <Justin Ridgewell> | But that'll go away with the real impl |
| 04:09 | <littledan> | Yes, the spec will have requirements, and we will also design a V8 API |