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Revert "timers: refactor to use optional chaining" #38245

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mcollina
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This reverts commit d8f535b.

As part of #37937, I tracked down a regression introduced by #36767.

With optional chaining:

Screenshot 2021-04-15 at 12 07 40

Without optional chanining:

Screenshot 2021-04-15 at 12 07 51

This sits in the hot path for HTTP.


I will recommend caution in adopting optional chaining in other areas of the Node.js.

@nodejs-github-bot nodejs-github-bot added needs-ci PRs that need a full CI run. timers Issues and PRs related to the timers subsystem / setImmediate, setInterval, setTimeout. labels Apr 15, 2021
@mcollina mcollina requested a review from ronag April 15, 2021 10:15
@Flarna
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Flarna commented Apr 15, 2021

Should we report this towards v8?

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ronag commented Apr 15, 2021

Yea this seems like a V8 issue. @nodejs/v8

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LGTM, gj

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@mcollina
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cc @nodejs/tsc

@targos
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targos commented Apr 15, 2021

I wanted to prove it with a benchmark and open a V8 issue but it seems optional chaining is mostly faster (at least with V8 8.9): https://jsben.ch/BwkJK

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ronag commented Apr 15, 2021

This reverts commit d8f535b.

As part of #37937, I tracked down a regression introduced by #36767.

With optional chaining:

Screenshot 2021-04-15 at 12 07 40

Without optional chanining:

Screenshot 2021-04-15 at 12 07 51

This sits in the hot path for HTTP.

I will recommend caution in adopting optional chaining in other areas of the Node.js.

@mcollina: What node version were you trying this on?

@mcollina
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I wanted to prove it with a benchmark and open a V8 issue but it seems optional chaining is mostly faster (at least with V8 8.9): https://jsben.ch/BwkJK

I have literally no clue why, but without optional chaining those function calls get inlined.

Those flamegraphs come from master.

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targos commented Apr 15, 2021

those function calls get inlined.

That's a good point, thanks. I'll try to do a different benchmark to show that optional chaining prevents inlining.

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targos commented Apr 16, 2021

those function calls get inlined.

That's a good point, thanks. I'll try to do a different benchmark to show that optional chaining prevents inlining.

It's not that easy. Everything gets inlined with this example:

'use strict';

function getPropClassic(obj) {
  return obj && obj.prop;
}

function getPropOptional(obj) {
  return obj?.prop;
}

const obj = { prop: 42 };

function testGetPropClassic(obj) {
  return getPropClassic(obj);
}

function testGetPropOptional(obj) {
  return getPropOptional(obj);
}

for (let i = 0; i < 1e6; i++) {
  testGetPropClassic(obj);
  testGetPropOptional(obj);
}
> node --trace-turbo-inlining bench.js
Considering 000002D5A0AE59D8 {0x004b3832c8e1 <SharedFunctionInfo testGetPropClassic>} for inlining with 000002D5A0AE59E8 {0x004b3832d821 <FeedbackVector[2]>}
Inlining small function(s) at call site #45:JSCall
Inlining 000002D5A0AE59D8 {0x004b3832c8e1 <SharedFunctionInfo testGetPropClassic>} into 000002D5A0AE4A98 {0x004b3832c779 <SharedFunctionInfo>}
Considering 000002D5A0AE63A8 {0x004b3832c841 <SharedFunctionInfo getPropClassic>} for inlining with 000002D5A0AE63B8 {0x004b3832d7e1 <FeedbackVector[2]>}
Inlining small function(s) at call site #80:JSCall
Inlining 000002D5A0AE63A8 {0x004b3832c841 <SharedFunctionInfo getPropClassic>} into 000002D5A0AE4A98 {0x004b3832c779 <SharedFunctionInfo>}
Considering 000002D5A0AE69E8 {0x004b3832c931 <SharedFunctionInfo testGetPropOptional>} for inlining with 000002D5A0AE6DF8 {0x004b3832d861 <FeedbackVector[2]>}
Inlining small function(s) at call site #50:JSCall
Inlining 000002D5A0AE69E8 {0x004b3832c931 <SharedFunctionInfo testGetPropOptional>} into 000002D5A0AE4A98 {0x004b3832c779 <SharedFunctionInfo>}
Considering 000002D5A0AE78A8 {0x004b3832c891 <SharedFunctionInfo getPropOptional>} for inlining with 000002D5A0AE78B8 {0x004b3832d7a1 <FeedbackVector[2]>}
Inlining small function(s) at call site #129:JSCall
Inlining 000002D5A0AE78A8 {0x004b3832c891 <SharedFunctionInfo getPropOptional>} into 000002D5A0AE4A98 {0x004b3832c779 <SharedFunctionInfo>}

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jasnell commented Apr 16, 2021

@targos I'm curious... Can you try that example but with obj replaced with a class with a getter?

class Obj { get prop() { return 42; }  }
const obj = new Obj()

Also, let's see what happens when you alternate calls between the argument being obj and undefined.

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LGTM

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nodejs-github-bot commented Apr 19, 2021

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"Build from tarball / test-tarball-linux (pull_request) " keeps failing. Is that required to pass for this landing? cc @BethGriggs

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Failure is js-native-api/test_object/test, which was mentioned as being fixed by #38000. Rerunning as that has just landed 🤞🏻

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I hadn't appreciated before that GH actions do not rebase. fc20e83 was the fix for the failure seen here (js-native-api/test_object/test). I think we should go ahead and land rather than rebase and rerun (due to the timing).

BethGriggs pushed a commit that referenced this pull request Apr 19, 2021
This reverts commit d8f535b.

PR-URL: #38245
Reviewed-By: Gerhard Stöbich <[email protected]>
Reviewed-By: Robert Nagy <[email protected]>
Reviewed-By: Richard Lau <[email protected]>
Reviewed-By: Antoine du Hamel <[email protected]>
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Zijian Liu <[email protected]>
Reviewed-By: Beth Griggs <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Michael Dawson <[email protected]>
Reviewed-By: Rich Trott <[email protected]>
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Landed in a0261d2

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