events: show throw stack trace for uncaught exception #19003

addaleax · 2018-02-26T14:51:09Z

Show the stack trace for the eventemitter.emit('error') call
in the case of an uncaught exception.

Previously, there would be no clue in Node’s output about where
the actual throw comes from.

In its current form, this patch would not modify err.stack if the exception is handled somewhere, and it redacts lines from the throw stack trace if they are duplicates of the original error stack trace (which likely occurs a lot).

Those design choices are up for debate :)

Checklist

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

Affected core subsystem(s)

events

mscdex · 2018-02-26T14:58:40Z

lib/events.js

@@ -98,6 +98,58 @@ EventEmitter.prototype.getMaxListeners = function getMaxListeners() {
  return $getMaxListeners(this);
 };

+// Returns the longest sequence of a that fully appears in b, of length >= 3.


Perhaps use backticks around variables in these comments, otherwise 'a' looks like the article and not the variable and is confusing.

benjamingr · 2018-02-26T15:31:02Z

I'm +1 on both the design choices (Only modifying if thrown, and removing duplicate lines).

I'm wondering if this has a measurable performance impact.

benjamingr

Very nice! I'd love some more tests - this is a nice improvement. I wonder how common creating the error in a different context from throwing it happens.

addaleax · 2018-02-26T16:54:10Z

I'm wondering if this has a measurable performance impact.

@benjamingr I would expect that if you write a benchmark that tests for it, it will show an impact. I wouldn’t include such a benchmark in our suite though; I don’t think creating a ton of error events without handlers is something that we should need to make as fast as possible.

I’ve also added more (but similar) tests, let me know if you had something specific in mind.

targos · 2018-02-26T20:49:26Z

lib/events.js

+}
+
+function enhanceStackTrace(err, own) {
+  const sep = '\nEmitted \'error\' event at at:\n';


duplicate "at"

targos · 2018-02-26T20:53:05Z

lib/events.js

+}
+
+const kExpandStack = Symbol('kExpandStack');
+Object.defineProperty(EventEmitter, 'kExpandStack', { value: kExpandStack });


is that made public on purpose?

@targos It’s non-enumerable, so most people will never find out it exists… I don’t think anybody is going to use it? How would we hide it?

Could it be exported by an internal module? Or is it too early in the bootstrapping process to do it?

@targos It’s fine, I’ve changes it – the worst case scenario is that this mechanism just doesn’t work and leaves the error unchanged.

BridgeAR

Could we add a test for process.on('uncaughtException', fn)? I guess right now that does not work together?

BridgeAR · 2018-03-01T22:17:29Z

lib/events.js

+    return [ l1, j1, i1 ];
+  else
+    return [ l2, i2, j2 ];
+}


This part confuses me. As far as I see it the common part will always be identical or do I miss something?

@BridgeAR Thanks for catching – it made sense in an earlier version of this code, but it’s removed now.

Show the stack trace for the `eventemitter.emit('error')` call in the case of an uncaught exception. Previously, there would be no clue in Node’s output about where the actual `throw` comes from.

addaleax · 2018-03-01T22:49:03Z

I guess right now that does not work together?

It (intentionally) does not, yes, mostly to keep existing behavior unchanged & avoid this being semver-major. I don’t feel strongly about it, though.

addaleax · 2018-03-02T10:50:15Z

CI: https://ci.nodejs.org/job/node-test-commit/16593/

addaleax · 2018-03-04T21:27:23Z

Landed in 68d508a

Show the stack trace for the `eventemitter.emit('error')` call in the case of an uncaught exception. Previously, there would be no clue in Node’s output about where the actual `throw` comes from. PR-URL: #19003 Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>

Show the stack trace for the `eventemitter.emit('error')` call in the case of an uncaught exception. Previously, there would be no clue in Node’s output about where the actual `throw` comes from. PR-URL: nodejs#19003 Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>

MylesBorins · 2018-04-13T04:27:42Z

Should this be backported to v8.x-staging? If yes please follow the guide and raise a backport PR, if not let me know or add the dont-land-on label.

Show the stack trace for the `eventemitter.emit('error')` call in the case of an uncaught exception. Previously, there would be no clue in Node’s output about where the actual `throw` comes from. PR-URL: nodejs#19003 Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>

nodejs-github-bot added events Issues and PRs related to the events subsystem / EventEmitter. lib / src Issues and PRs related to general changes in the lib or src directory. labels Feb 26, 2018

mscdex reviewed Feb 26, 2018

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benjamingr approved these changes Feb 26, 2018

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jasnell approved these changes Feb 26, 2018

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targos reviewed Feb 26, 2018

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addaleax force-pushed the events-stack branch from dafe586 to 2d8e7ed Compare February 26, 2018 21:23

BridgeAR reviewed Mar 1, 2018

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addaleax added 5 commits March 1, 2018 22:33

events: show throw stack trace for uncaught exception

c5b6a2d

Show the stack trace for the `eventemitter.emit('error')` call in the case of an uncaught exception. Previously, there would be no clue in Node’s output about where the actual `throw` comes from.

[squash] better comment text

3017598

[squash] more tests

3c3fa83

[squash] remove at at

70457e0

[squash] hide internals better

9cb8461

addaleax force-pushed the events-stack branch from 80e1084 to dcc9873 Compare March 1, 2018 22:47

[squash] bridgear comments

92b6be1

addaleax force-pushed the events-stack branch from dcc9873 to 92b6be1 Compare March 1, 2018 22:48

addaleax added the author ready PRs that have at least one approval, no pending requests for changes, and a CI started. label Mar 2, 2018

addaleax closed this Mar 4, 2018

addaleax removed the author ready PRs that have at least one approval, no pending requests for changes, and a CI started. label Mar 4, 2018

addaleax deleted the events-stack branch March 4, 2018 21:27

MylesBorins mentioned this pull request Mar 6, 2018

v9.8.0 proposal #19181

Merged

MylesBorins added the dont-land-on-v6.x label Apr 13, 2018

MylesBorins added the backport-requested-v8.x label Apr 13, 2018

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events: show throw stack trace for uncaught exception #19003

events: show throw stack trace for uncaught exception #19003

addaleax commented Feb 26, 2018

mscdex Feb 26, 2018 •

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addaleax Feb 26, 2018

benjamingr commented Feb 26, 2018 •

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addaleax commented Feb 26, 2018

targos Feb 26, 2018

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addaleax commented Mar 4, 2018

MylesBorins commented Apr 13, 2018

events: show throw stack trace for uncaught exception #19003

events: show throw stack trace for uncaught exception #19003

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addaleax commented Feb 26, 2018

Checklist

Affected core subsystem(s)

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addaleax commented Mar 1, 2018

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MylesBorins commented Apr 13, 2018

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