async_hooks: remove experimental onPropagate option #46386

jasnell · 2023-01-27T22:08:13Z

The onPropagate option for AsyncLocalStorage is problematic for a couple of reasons:

It is not expected to be forwards compatible in any way with the upcoming TC-39 AsyncContext proposal.
It introduces a non-trivial O(n) cost invoking a JavaScript callback for every AsyncResource that is created, including every Promise.

While it is still experimental, I recommend removing it while we can revisit the fundamental use cases in light of the coming AsyncContext proposal.

/cc @nodejs/async_hooks

Qard

LGTM, though @Flarna may have some thoughts as I believe they're depending on this interface. Not sure how critical it is but they may want a viable alternative proposed before this can be removed.

vdeturckheim

lgtm - aligned with @Qard here

GeoffreyBooth

I like the idea of aligning our development of this with WinterCG.

I don’t really accept that it’s our responsibility to develop replacements for any users depending on an experimental API. If they want a new feature in Node, they should propose and contribute it.

jasnell · 2023-01-28T02:07:09Z

If they want a new feature in Node, they should propose and contribute it.

Well, to be fair, that's exactly what @Flarna did :-) ... There's no rush pushing this out. We can give Flarna time to revisit if they want.

Qard · 2023-01-28T05:07:44Z

To be clear, I'm fine removing it as long as @Flarna doesn't feel it's too disruptive. I'm not aware of anyone else using it.

doc/api/async_context.md

Flarna · 2023-01-30T21:47:09Z

2. It introduces a non-trivial O(n) cost invoking a JavaScript callback for every AsyncResource that is created, including every Promise.

Actually the O(n) cost is not introduced by onPropagate. If set each resource will trigger one call. O(n) will only happen if there are n ALS instances using onPropagate.
The O(n) complexity is already there independent of onPropagate because ALS uses the init hook to propagate context internally in all ALS instances.

Anyhow, following TC-39 sounds reasonable. Any hints that TC-39 will accept the AsyncContext proposal anytime soon? As far as I know the proposal is a few years old meanwhile and has still not reached stage 1. Or is there something ongoing which is not visible on the TC-39 propsals github repo?

lib/async_hooks.js

jasnell · 2023-01-30T21:53:58Z

Anyhow, following TC-39 sounds reasonable. Any hints that TC-39 will accept the AsyncContext proposal anytime soon? As far as I know the proposal is a few years old meanwhile and has still not reached stage 1. Or is there something ongoing which is not visible on the TC-39 propsals github repo?

Work is underway now. With @jridgewell, @legendecas, and @littledan heading it up.

Refs: nodejs#46374 The `onPropagate` option for `AsyncLocalStorage` is problematic for a couple of reasons: 1. It is not expected to be forwards compatible in any way with the upcoming TC-39 `AsyncContext` proposal. 2. It introduces a non-trivial O(n) cost invoking a JavaScript callback for *every* AsyncResource that is created, including every Promise. While it is still experimental, I recommend removing it while we can revisit the fundamental use cases in light of the coming `AsyncContext` proposal.

nodejs-github-bot · 2023-01-30T22:49:01Z

CI: https://ci.nodejs.org/job/node-test-pull-request/49267/

jridgewell · 2023-01-30T23:20:30Z

Anyhow, following TC-39 sounds reasonable. Any hints that TC-39 will accept the AsyncContext proposal anytime soon?

We'll have a better idea of how long it will take after the TC39 meeting this week.

For now, I think it's better to think of this as aligning with the implementation strategy that AsyncContext will take, which will make everything considerably faster. It's possible that V8 will add a special hook for Node to control how the propagation works (they same way they've added support for async_hooks), but that has the potential to impact the performance guarantees that AsyncContext requires to be part of the core language.

As far as I know the proposal is a few years old meanwhile and has still not reached stage 1. Or is there something ongoing which is not visible on the TC-39 propsals github repo?

I've been meeting with delegates for a few weeks getting feedback on the proposal. We've gotten approval from the security folks, which was a major blocker the last time this was presented. We also have a private matrix channel to discuss that will become public when we get accepted to Stage 1.

legendecas · 2023-01-31T02:18:29Z

The O(n) complexity is already there independent of onPropagate because ALS uses the init hook to propagate context internally in all ALS instances.

Value propagation can be optimized to avoid the complexity with the number of AsyncLocalStorage instances, as the propagation doesn't calling into user code. See https://github.com/legendecas/proposal-async-context/blob/master/src/index.ts#L7 for an example.

nodejs-github-bot · 2023-01-31T02:24:58Z

CI: https://ci.nodejs.org/job/node-test-pull-request/49270/

nodejs-github-bot · 2023-02-01T15:20:22Z

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- Loading data for nodejs/node/pull/46386
✔  Done loading data for nodejs/node/pull/46386
----------------------------------- PR info ------------------------------------
Title      async_hooks: remove experimental onPropagate option (#46386)
Author     James M Snell  (@jasnell)
Branch     jasnell:remove-asynclocalstorage-onpropagate -> nodejs:main
Labels     async_hooks, author ready
Commits    1
 - async_hooks: remove experimental onPropagate option
Committers 1
 - James M Snell 
PR-URL: https://github.com/nodejs/node/pull/46386
Refs: https://github.com/nodejs/node/issues/46374
Reviewed-By: Stephen Belanger 
Reviewed-By: Vladimir de Turckheim 
Reviewed-By: Geoffrey Booth 
Reviewed-By: Benjamin Gruenbaum 
Reviewed-By: Gerhard Stöbich 
Reviewed-By: Chengzhong Wu 
------------------------------ Generated metadata ------------------------------
PR-URL: https://github.com/nodejs/node/pull/46386
Refs: https://github.com/nodejs/node/issues/46374
Reviewed-By: Stephen Belanger 
Reviewed-By: Vladimir de Turckheim 
Reviewed-By: Geoffrey Booth 
Reviewed-By: Benjamin Gruenbaum 
Reviewed-By: Gerhard Stöbich 
Reviewed-By: Chengzhong Wu 
--------------------------------------------------------------------------------
   ℹ  This PR was created on Fri, 27 Jan 2023 22:08:13 GMT
   ✔  Approvals: 6
   ✔  - Stephen Belanger (@Qard): https://github.com/nodejs/node/pull/46386#pullrequestreview-1273599442
   ✔  - Vladimir de Turckheim (@vdeturckheim): https://github.com/nodejs/node/pull/46386#pullrequestreview-1273608580
   ✔  - Geoffrey Booth (@GeoffreyBooth) (TSC): https://github.com/nodejs/node/pull/46386#pullrequestreview-1273724192
   ✔  - Benjamin Gruenbaum (@benjamingr): https://github.com/nodejs/node/pull/46386#pullrequestreview-1273975929
   ✔  - Gerhard Stöbich (@Flarna): https://github.com/nodejs/node/pull/46386#pullrequestreview-1276087836
   ✔  - Chengzhong Wu (@legendecas) (TSC): https://github.com/nodejs/node/pull/46386#pullrequestreview-1276289905
   ✔  Last GitHub CI successful
   ℹ  Last Full PR CI on 2023-01-31T02:24:58Z: https://ci.nodejs.org/job/node-test-pull-request/49270/
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- Bringing origin/main up to date...
From https://github.com/nodejs/node
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--------------------------------------------------------------------------------
[main 60f40eb7a8] async_hooks: remove experimental onPropagate option
 Author: James M Snell 
 Date: Fri Jan 27 14:03:51 2023 -0800
 3 files changed, 6 insertions(+), 79 deletions(-)
 delete mode 100644 test/async-hooks/test-async-local-storage-stop-propagation.js
   ✔  Patches applied
--------------------------------------------------------------------------------
   ✖  Git found no trailers in the original commit message, but 'Refs: https://github.com/nodejs/node/issues/46374' is present and should be a trailer.

https://github.com/nodejs/node/actions/runs/4065850372

The `onPropagate` option for `AsyncLocalStorage` is problematic for a couple of reasons: 1. It is not expected to be forwards compatible in any way with the upcoming TC-39 `AsyncContext` proposal. 2. It introduces a non-trivial O(n) cost invoking a JavaScript callback for *every* AsyncResource that is created, including every Promise. While it is still experimental, I recommend removing it while we can revisit the fundamental use cases in light of the coming `AsyncContext` proposal. Refs: #46374 PR-URL: #46386 Reviewed-By: Stephen Belanger <[email protected]> Reviewed-By: Vladimir de Turckheim <[email protected]> Reviewed-By: Geoffrey Booth <[email protected]> Reviewed-By: Benjamin Gruenbaum <[email protected]> Reviewed-By: Gerhard Stöbich <[email protected]> Reviewed-By: Chengzhong Wu <[email protected]>

jasnell · 2023-02-01T15:37:34Z

Landed in dc90810

The `onPropagate` option for `AsyncLocalStorage` is problematic for a couple of reasons: 1. It is not expected to be forwards compatible in any way with the upcoming TC-39 `AsyncContext` proposal. 2. It introduces a non-trivial O(n) cost invoking a JavaScript callback for *every* AsyncResource that is created, including every Promise. While it is still experimental, I recommend removing it while we can revisit the fundamental use cases in light of the coming `AsyncContext` proposal. Refs: #46374 PR-URL: #46386 Reviewed-By: Stephen Belanger <[email protected]> Reviewed-By: Vladimir de Turckheim <[email protected]> Reviewed-By: Geoffrey Booth <[email protected]> Reviewed-By: Benjamin Gruenbaum <[email protected]> Reviewed-By: Gerhard Stöbich <[email protected]> Reviewed-By: Chengzhong Wu <[email protected]>

jasnell requested review from Flarna and Qard January 27, 2023 22:08

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jasnell force-pushed the remove-asynclocalstorage-onpropagate branch from c08df91 to 3c265fa Compare January 30, 2023 21:59

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Flarna mentioned this pull request Feb 1, 2023

Revisit the AsyncLocalStorage onPropagate option #46374

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MylesBorins mentioned this pull request Feb 19, 2023

v19.7.0 proposal #46725

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danielleadams mentioned this pull request Apr 11, 2023

v18.16.0 release proposal #47502

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async_hooks: remove experimental onPropagate option #46386

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async_hooks: remove experimental onPropagate option #46386

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