Summit topic: Promises

[MayaLekova]

Creating this issue in attempt to gather links and offline discussion relevant to what's happening around the Promises topic.

Motivation:

Make promises and other asynchronous primitives competitive performance-wise to traditional callback-oriented programming and easier to trace and debug.

• Why do we want to use promises and async/await?
• Recent optimization effort done in V8 and follow-up issues.
• Gathering real-world usage scenarios.
• V8 API for promises
• Improving debugging for promises in Node.js
• Other related sub-topics - async hooks, zones.

Events:

• 9:30 - 10:00 (main space) Talk: Holding on to your Performance Promises @bmeurer @MayaLekova
• 13:30 - 15:00 (meeting room) Workshop: Promises @bmeurer @benjamingr

Resources:

// Please add whatever you feel contributes to the discussion
// Talk slides to be linked here

[benjamingr]

Hey @MayaLekova thank you for opening this :) Looking forward to your workshop about promise performance!

A couple of us have written user use-cases with promises in: https://github.com/nodejs/promise-use-cases and what userland libraries currently do better.

Namely, after doing a community survey, going over code on GitHub and asking around and also based on my own intuition being involved with bluebird and other promise libraries for a while and answering 700 SO questions - what I saw most and intend to discuss written here is:

• Debugging issues like issues with unhandledRejection hooks and debugging or people using .catch(error => console.log("error") and why they do that
• Several user errors people run into a lot like forgetting to return a promise, forgetting to await, resolveing/rejecting multiple times, have never resolving promises, using promises in a forEach or getting deadlocks
• Problematic usage patterns like explicit construction, having a hard time creating promises correctly,
• People ask how promises work in Node.js and we don't have material ready about it.
• It is currently impossible/very hard to use testing libraries like lolex with promises, or mock race conditions.
• People are having a hard time with stack traces when testing, or when debugging production issues and postmortem is an open issue.
• People still use userland libraries like bluebird and maybe avoid async iterators.
• There are a lot of things people ask for like hooks for context, the ability to build cancellation (also 2) or use it in a standardized way

I don't want to suggest any actions but rather bring the issues up and discuss them and see what the people attending the workshop think about any of these. My personal feeling is that people I talked to felt the most strongly about testing async functions being hard and stack traces - but I hope to get some interesting discussion going :)

[bmeurer]

Woah. Thanks @MayaLekova for kicking this off, and thanks @benjamingr for this nicely structured list of use cases! Looks like there's a lot to discuss for us. 👍

[benjamingr]

I think it's perhaps worth setting out goals for the workshop and align expectations.

My personal goals for the promise workshop at the summit are:

• Discuss the community use cases we gathered (big props and acknowledgements to @MadaraUchiha @getify @spion @bjouhier and @itaysabato as well as others for help with that and the repo).
• Figure out what features these use cases translate to, prioritise them together and see what is actionable and what some tradeoffs might be.
• Come up with a plan for continuing these discussion and maybe a process for soliciting more community feedback.
• Learn more about how promises work in V8.

I don't think we'll get concrete solutions or features since there is a lot of discussion to be had. I hope to learn a lot from the experience of others, meet interesting people who share a passion for making developers' debugging experience better and add a perspective on user debugging experience.

[bmeurer]

@benjamingr That matches my expectations. We hope to develop a better understanding of the needs of developers specifically on the Node side, so that we can drive future work on V8 in the right direction. 👍

[MayaLekova]

Being pretty new to this topic, my expectations are also around listening to what's important for the community, so we can better focus our efforts in V8.
Thank you for structuring this use cases so well!

[benjamingr]

Hey, really nice talk @MayaLekova and @bmeurer !

Some discussion points:

• We've had the same issues with monitoring and setScheduler in bluebird where the scheduling bypass interfered with change detection people used in Angular
• I'd love to see some performance measures of coroutines as async/await vs. async/await and how important the actual ability to hook on microtick scheduling semantics.
• I'd love to talk about why the spec works this way, the whole "delaying a microtick" issue was due to a real concern (avoiding zalgo) but there is no reason I can think of that the spec couldn't/shouldn't allow elision of promises in that scenario - have you considered bringing it up with TC39?

[JiaLiPassion]

@benjamingr ,for the bluebird angular issue, it has been resolved in zone.js, the document can be found here, https://github.com/angular/zone.js/blob/master/NON-STANDARD-APIS.md (search bluebird).

@bmeurer And I want to know current ES2017 native async/await use native promise which can not intercepted, in nodejs , we can use asynchooks and PromiseHooks, but in browser, currently we can not do anything about it. Is PromiseHooks or AsyncHooks javascript API for in the future plan?

Thank you.

[benjamingr]

@JiaLiPassion Zones are a no-go for Node.js at the moment due to the error handling issues, which is sort of a shame since a lot of us are using promises now (and the issue is basically about nested callbacks).

[bmeurer]

@JiaLiPassion that's something to discuss with @domenic and @benlesh

[benjamingr]

Interesting discussion in the Diagnostics session about zones and async_hooks - I think the current PoV is that Node.js needs to figure out async_hooks error handling before we unblock zones.

[JiaLiPassion]

@benjamingr , @bmeurer , got it, thank you!

[benjamingr]

@JiaLiPassion see the discussion in domenic/zones#9 (comment)

The part that changed since 2 years ago is that async/await has risen a lot in popularity and it doesn't suffer from the same problem. Then again for async/await zones are probably less important than being to hook into just the scheduling.

[JiaLiPassion]

@benjamingr , yeah, currently the issue is in angular and rxjs test, in the near future , if user want to compile typescript codeintoES2017 targetwithasync/await, zone.jscan't control thenative promise. So user will need to handle change detectionandasync test` themselves.

[benjamingr]

@JiaLiPassion IIRC Ben Lesh said "IE11 is saving the internet". :D

This is something I plan to bring up in the second session - but TC39 is going to need to solve this for async functions and not Node.js. Feel free to open an issue in https://github.com/nodejs/promise-use-cases

[JiaLiPassion]

@benjamingr , got it, I will!

[mcollina]

Join from PC, Mac, Linux, iOS or Android: https://zoom.us/j/903800260

Or iPhone one-tap :
US: +16465588656,,903800260# or +16699006833,,903800260#
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Dial(for higher quality, dial a number based on your current location):
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Meeting ID: 903 800 260
International numbers available: https://zoom.us/u/dBA97SNb0

[benjamingr]

@MayaLekova can you post the meeting notes :)?

[MayaLekova]

Here are the meeting notes
The #number in the notes reference slide titles from @benjamingr slides (if you can share them as well would be awesome!).

[benjamingr]

https://docs.google.com/presentation/d/16WYzlvvDm85IruD3jkH2nTwTkTUa6YSPtDF0VQ4g4Hk/edit?usp=sharing

[benjamingr]

PTAL https://github.com/petkaantonov/bluebird/pull/1530/files

[MayaLekova]

Takeaways

[benjamingr]

@bmeurer @MayaLekova two questions:

• Can we close this issue? (Or do you want to do another session today?)
• Can/should we schedule a follow-up meeting online on this in a month (two?)?

[bmeurer]

I have to leave early today, but I'm happy to talk about promises in the morning. I'd say we can close this.

[benjamingr]

https://doodle.com/poll/3wdzdfzikmcvndee

[benjamingr]

Thanks for participating everything I learned a lot and I think a lot of good progress was made. Please consider filling the doodle above if you haven't already. Also pinging @BridgeAR @addaleax @littledan in case either of them would like to also participate in the follow up discussion.

[littledan]

@benjamingr Apologies for my delay; I've filled out the doodle.

[BridgeAR]

The same here.

[benjamingr]

Great, thanks for the update - going to wait for another day or two to see if anyone else wants to participate -the most likely candidate is Thu, Jul 12 @ 3:30 PM UTC unless we can figure out something that also works for @ljharb