timers: run nextTicks after each immediate and timer #22842

apapirovski · 2018-09-13T14:48:57Z

In order to better match browser behaviour, run nextTicks (and subsequently the microtask queue) after each individual Timer and Immediate, rather than after the whole list is processed. The current behaviour is somewhat of a performance micro-optimization and also partly dictated by how timer handles were implemented.

This will have a significant impact on how promises are resolved/rejected (due to changes to the microtask queue timing) which is IMO a reasonably important change.

@Fishrock123 already started some work on this in #22316 but I spun this off into a separate PR as I had good understanding of what needed to happen to actually pass the tests.

I still likely need to update the docs and write a few tests. This is also definitely semver-major. This will also need a CitGM run.

Fixes: #22257

Checklist

make -j4 test (UNIX), or vcbuild test (Windows) passes
tests and/or benchmarks are included
commit message follows commit guidelines

nodejs-github-bot · 2018-09-13T14:49:00Z

@apapirovski build started: https://ci.nodejs.org/blue/organizations/jenkins/node-test-pull-request-lite-pipeline/detail/node-test-pull-request-lite-pipeline/877/pipeline

apapirovski · 2018-09-13T14:50:29Z

CI: https://ci.nodejs.org/job/node-test-pull-request/17170/
CitGM: https://ci.nodejs.org/view/Node.js-citgm/job/citgm-smoker/1542/ and master: https://ci.nodejs.org/view/Node.js-citgm/job/citgm-smoker/1543/

apapirovski · 2018-09-13T15:02:20Z

Ok, looks like test/parallel/test-domain-with-abort-on-uncaught-exception.js might be made flaky by this change. I'll have to dig into that test. Doesn't fail for me locally and it succeeded in the full CI hence the flaky assumption.

Stress test: https://ci.nodejs.org/job/node-stress-single-test/2014/ and against master: https://ci.nodejs.org/job/node-stress-single-test/2015/

Edit: Also parallel/test-child-process-ipc-next-tick might be made flaky by this. I'm guessing that these are both related to the change in timers.

mscdex · 2018-09-13T15:32:03Z

Can we get some benchmarks to show just what kind of performance hit we should expect from this?

apapirovski · 2018-09-13T16:04:01Z

@mscdex Yup, I'm hoping to first figure out if we can get all the tests to pass and CitGM to work before I go down the road of trying to figure out performance and maybe optimize that.

joaocgreis · 2018-09-13T19:53:53Z

@apapirovski had to abort the CitGM run to restart Jenkins, two workers didn't finish. Can you restart it if needed? I started the master run after rebooting, link above is correct.

addaleax · 2018-09-13T21:17:42Z

lib/timers.js

@@ -264,7 +264,7 @@ function listOnTimeout(list, now) {

  debug('timeout callback %d', msecs);

-  var diff, timer;
+  var diff, ran, timer;


ran what? :)

I kno, I kno 😆 I'll make it more descriptive. But to answer the question: an iteration of the loop right after it.

apapirovski · 2018-09-14T01:32:16Z

There are currently 3 test failures. They are:

test/sequential/test-http-keepalive-maxsockets.js (see test: move test-http-keepalive-maxsockets to sequential #16777)
This is a flaky test that was moved to sequential. I'll dig in but I assume this test has a weird interaction with when nextTicks are executed. I think this test is flaky and needs fixing, rather than it highlighting anything wrong with this PR.
test/parallel/test-child-process-ipc-next-tick.js
This one might be showcasing a real bug. I will need to confirm.
test/parallel/test-domain-with-abort-on-uncaught-exception.js
I don't even know where to start but again, seems like potentially a real bug.

apapirovski · 2018-09-14T02:25:19Z

CI: https://ci.nodejs.org/job/node-test-pull-request/17179/
CitGM: https://ci.nodejs.org/view/Node.js-citgm/job/citgm-smoker/1544/

I believe that all 3 test failures above were related to incorrect error resolution inside processImmediates. I had to make some changes for the way the new nextTicks are run.

starkwang · 2018-09-14T02:25:51Z

Should we add some documents about this behavior change?

apapirovski · 2018-09-14T03:14:10Z

I think we're in the clear on tests now so here's benchmarks:

https://ci.nodejs.org/view/Node.js%20benchmark/job/benchmark-node-micro-benchmarks/238/

I will be working on new tests for this behaviour and documentation later today or tomorrow. I'll also follow up with perf improvements as necessary.

Results:

 timers/immediate.js type='breadth1' n=5000000                         *     -3.25 %       ±2.61%  ±3.44%  ±4.41%
 timers/immediate.js type='breadth4' n=5000000                        **     -2.74 %       ±1.74%  ±2.30%  ±2.95%
 timers/immediate.js type='breadth' n=5000000                        ***     -7.91 %       ±2.09%  ±2.75%  ±3.53%
 timers/immediate.js type='clear' n=5000000                           **     -2.48 %       ±1.64%  ±2.17%  ±2.78%
 timers/immediate.js type='depth1' n=5000000                         ***     -3.80 %       ±1.39%  ±1.84%  ±2.36%
 timers/immediate.js type='depth' n=5000000                            *     -1.19 %       ±1.18%  ±1.55%  ±1.99%
 timers/set-immediate-breadth-args.js n=5000000                      ***     -5.80 %       ±1.83%  ±2.41%  ±3.09%
 timers/set-immediate-breadth.js n=10000000                          ***     -6.23 %       ±1.88%  ±2.48%  ±3.18%
 timers/set-immediate-depth-args.js n=5000000                        ***     -2.43 %       ±0.90%  ±1.19%  ±1.53%
 timers/timers-breadth.js n=5000000                                  ***     -7.07 %       ±3.33%  ±4.39%  ±5.64%
 timers/timers-cancel-pooled.js n=5000000                                    -5.77 %       ±7.09%  ±9.35% ±12.01%
 timers/timers-cancel-unpooled.js direction='end' n=1000000                   9.24 %      ±10.52% ±13.87% ±17.81%
 timers/timers-cancel-unpooled.js direction='start' n=1000000                 2.14 %       ±5.43%  ±7.16%  ±9.19%
 timers/timers-depth.js n=1000                                         *     -0.06 %       ±0.06%  ±0.08%  ±0.10%
 timers/timers-insert-pooled.js n=5000000                                    -1.71 %       ±2.13%  ±2.81%  ±3.61%
 timers/timers-insert-unpooled.js direction='end' n=1000000                  -0.99 %       ±1.39%  ±1.84%  ±2.36%
 timers/timers-insert-unpooled.js direction='start' n=1000000                -2.18 %       ±2.78%  ±3.66%  ±4.70%
 timers/timers-timeout-pooled.js n=10000000                          ***    -38.68 %       ±2.94%  ±3.88%  ±4.99%
 timers/timers-timeout-unpooled.js n=1000000                         ***    -37.78 %       ±2.35%  ±3.11%  ±3.99%

Given the perf improvements here #20555, I think we can live with the timers-timeout regressions but I'll be doing some work to minimize it.

Fishrock123 · 2018-09-17T16:40:17Z

lib/timers.js

-  let refCount = 0;
+  if (queue !== outstandingQueue) {
+    queue.head = queue.tail = null;
+    immediateInfo[kHasOutstanding] = 1;


Maybe we could leave a comment here about how this = null thing works? it's... pretty difficult to read/understand.

we should disallow that in the lint rules. please split it into two.

Fishrock123 · 2018-09-17T16:41:05Z

lib/timers.js

+    if (ran)
+      runNextTicks();
+    else
+      ran = true;


Ditto on comments here and above where we use the same pattern, easy to misunderstand

Fishrock123

Seems fine to me, but it certainly confusing, implementation-wise.

We should probably CITGM this, it seems slightly ecosystem-risky to me? Don't think it's necessarily major by default though.

Edit: Re - benchmarks; maybe we can do some extra optimization there. I'll try to take profiles.

Fishrock123 · 2018-09-17T17:12:21Z

oof, this change is.. kinda expensive.

Here are the numbers I got for timers/timers-timeout-pooled.js n=10000000

master: 14,202,832.177390624
this patch: 5,709,151.565629168

Profiles:

apapirovski · 2018-09-17T20:49:31Z

^ that seems worse than the benchmark CI run. But it's not generally surprising, it now has to run nextTicks on each timer which necessitates crossing over to C++ for each timer. The question is how frequent of an occurrence this is and whether this is a sacrifice we're willing to make for correctness.

mscdex · 2018-09-18T03:21:17Z

Perhaps running these changes against some real-world scenarios (e.g. acmeair, etc.) might help answer some of this?

Fishrock123 · 2018-09-18T15:16:27Z

The question is how frequent of an occurrence this is

Promise-based code is the most likely candidate here. the question is, do people really do lots of async promise stuff in timeouts? I don't really know but I do feel like I usually don't do much async stuff in timeouts.

apapirovski · 2018-09-28T16:25:18Z

I'm planning to revisit this again over the weekend. Hopefully tidy up some of the perf and get some clearer practical results.

apapirovski · 2018-10-13T17:27:37Z

New benchmarks after more optimizations: https://ci.nodejs.org/view/Node.js%20benchmark/job/benchmark-node-micro-benchmarks/245/

sam-github · 2018-10-13T23:27:47Z

I think this is a good idea, it simplifies the API and makes it much more consistent.

nodejs/nodejs.org#1804 for example describes some confusion about when the tick queue is cleared, and some attempts to make the docs describe the behaviour.

Does this PR clear the tick queue only after timer callbacks, or does it do so after immediates are run, too? Both would be useful, IMO.

Trott · 2018-10-18T03:39:16Z

Landed in e7af983

Check that $TRAVIS_COMMIT_RANGE is set before trying to lint commit messages in Travis CI. Refs: #23572 (comment) Refs: #22842 (comment) PR-URL: #23725 Reviewed-By: Anatoli Papirovski <[email protected]> Reviewed-By: James M Snell <[email protected]> Reviewed-By: Luigi Pinca <[email protected]> Reviewed-By: Matheus Marchini <[email protected]>

In order to better match the browser behaviour, run nextTicks (and subsequently the microtask queue) after each individual Timer and Immediate, rather than after the whole list is processed. The current behaviour is somewhat of a performance micro-optimization and also partly dictated by how timer handles were implemented. PR-URL: #22842 Fixes: #22257 Reviewed-By: Anna Henningsen <[email protected]> Reviewed-By: Gus Caplan <[email protected]> Reviewed-By: Jeremiah Senkpiel <[email protected]> Reviewed-By: James M Snell <[email protected]> Reviewed-By: Ruben Bridgewater <[email protected]>

Check that $TRAVIS_COMMIT_RANGE is set before trying to lint commit messages in Travis CI. Refs: #23572 (comment) Refs: #22842 (comment) PR-URL: #23725 Reviewed-By: Anatoli Papirovski <[email protected]> Reviewed-By: James M Snell <[email protected]> Reviewed-By: Luigi Pinca <[email protected]> Reviewed-By: Matheus Marchini <[email protected]>

Node.js v11.x introduced a difference with how timers are run that results in some about ids in the blacklisted tests being off. Needs investigation but, regardless, should be fixed by T206222 See nodejs/node#22842 Bug: T206222 Change-Id: I9f0f906390d763ea52c61c9ae586da13172d687e

OmarDarwish · 2018-12-26T19:25:10Z

I tried to clarify how this behaves before this change landed in v11 nodejs/nodejs.org#1804

It was a little unclear for me when the nextTickQueue is processed (see this StackOverflow question). After some experimentation and more googling, re-write to make it more clear.

Deduplication section appears to be describing how things worked prior to nodejs/node#22842, so is no longer correct. The output in 11.12 is ``` setImmediate 1 process.nextTick a process.nextTick b setImmediate 2 process.nextTick a process.nextTick b ```

ghost · 2019-03-19T02:00:24Z

@apapirovski：Would you mind reviewing the article nodejs/nodejs.org#2158, if you are free

…-nexttick.md' (#2158) Deduplication section appears to be describing how things worked prior to nodejs/node#22842, so is no longer correct.

nodejs-github-bot added the timers Issues and PRs related to the timers subsystem / setImmediate, setInterval, setTimeout. label Sep 13, 2018

apapirovski added the semver-major PRs that contain breaking changes and should be released in the next major version. label Sep 13, 2018

addaleax reviewed Sep 13, 2018

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apapirovski force-pushed the next-ticks-after-each-timer-and-immediate branch from e7b20ce to 82e1515 Compare September 14, 2018 02:23

Fishrock123 reviewed Sep 17, 2018

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devsnek mentioned this pull request Sep 19, 2018

implement queueMicrotask #22951

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addaleax approved these changes Sep 24, 2018

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Fishrock123 mentioned this pull request Sep 26, 2018

MacroTask and MicroTask execution order #22257

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apapirovski force-pushed the next-ticks-after-each-timer-and-immediate branch from 82e1515 to ff24a20 Compare October 13, 2018 17:25

apapirovski force-pushed the next-ticks-after-each-timer-and-immediate branch from 88792fe to b6e4f68 Compare October 13, 2018 18:11

sam-github force-pushed the master branch from 882e022 to 9ed4646 Compare October 13, 2018 18:20

Trott closed this Oct 18, 2018

apapirovski mentioned this pull request Oct 21, 2018

11.0.0 proposal #23230

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Zirro mentioned this pull request Oct 28, 2018

Fix and run tests on Node.js v11 jsdom/jsdom#2406

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Fishrock123 mentioned this pull request Nov 6, 2018

timers: run nextTicks + MTQ between timers / immediates #22316

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refack mentioned this pull request Nov 19, 2018

flaky: parallel/test-timers-immediate-queue #24497

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OmarDarwish mentioned this pull request Dec 26, 2018

Clarify when nextTickQueue is processed nodejs/nodejs.org#1804

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ljianshu mentioned this pull request Jan 16, 2019

浏览器与Node的事件循环(Event Loop)有何区别? ljianshu/Blog#54

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XueSeason mentioned this pull request Mar 7, 2019

第 25 题：浏览器和Node 事件循环的区别 Advanced-Frontend/Daily-Interview-Question#26

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bughit mentioned this pull request Mar 18, 2019

remove the outdated Deduplication section from event-loop-timers-and-nexttick.md nodejs/nodejs.org#2158

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jilvin mentioned this pull request Apr 14, 2020

Use of process.nextTick() at db/users.js passport/todos-express-password#23

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Ziphwy mentioned this pull request Nov 11, 2020

NodeJS 系列之事件循环 Ziphwy/Blog#10

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Ayase-252 mentioned this pull request Aug 24, 2021

Event Loop performance different in different version nodejs/help#3512

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This was referenced Sep 3, 2021

Update 3.6 Event Loop.md nswbmw/node-in-debugging#17

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3.6节执行结果有误 nswbmw/node-in-debugging#15

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