process: add --unhandled-rejections flag #26599

BridgeAR · 2019-03-11T20:32:15Z

This adds a flag to define the default behavior for unhandled
rejections. Three modes exist: none, warn and strict. The first
is going to silence all unhandled rejection warnings. The second
behaves identical to the current default with the excetion that no
deprecation warning will be printed and the last is going to throw
an error for each unhandled rejection, just as regular exceptions do.
It is possible to intercept those with the uncaughtException hook
as with all other exceptions as well.

This PR has no influence on the existing unhandledRejection hook.
If that is used, it will continue to function as before.

Supersedes #20097

// CC @nodejs/diagnostics @nodejs/promises-debugging @nodejs/tsc

Checklist

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

nodejs-github-bot · 2019-03-11T20:32:17Z

@BridgeAR build started: https://ci.nodejs.org/blue/organizations/jenkins/node-test-pull-request-lite-pipeline/detail/node-test-pull-request-lite-pipeline/2871/pipeline

mmarchini · 2019-03-11T20:50:50Z

Code changes and proposed modes LGTM. If you don't mind, I want to investigate how this works with postmortem/llnode before we land. I'm not sure calling process.abort() is the best approach in this case and I think the stackTraceLimit reset trick to speed up Error creation might interfere with recent developments to make llnode more useful when investigating unhandled promise rejections (see https://chromium-review.googlesource.com/c/v8/v8/+/1405568 and nodejs/llnode#271).

lib/internal/process/promises.js

ljharb

Although I'd still prefer the deprecation warning be removed in the default case, I'm glad it's removed when an explicit flag is passed.

lib/internal/process/promises.js

src/node_options.cc

benjamingr

LGTM

doc/api/cli.md

src/node_options.h

src/node_options.cc

mcollina

LGTM

BridgeAR · 2019-03-12T14:36:15Z

I had to rebase due to conflicts, so PTAL.

CI https://ci.nodejs.org/job/node-test-pull-request/21457/

mmarchini · 2019-03-12T16:07:13Z

From a postmortem/llnode perspective (with the flags --unhandled-rejections=strict and --abort-on-uncaught-exception set):

The stack we get on the output is correct in most common cases (when we reject or throw inside a Promise/async function by passing an error to reject/throw.
The ReportException called inside TriggerFatalException will turn the JSArray stack stored in the Error object into its stringified version, and the frames stored in the JSArray will be deleted. This will render src: inspcet arguments from an Error object stack llnode#271 useless, but this is how V8 works and I think we should make changes there instead of blocking this PR because of it.
The stack we get on llnode (by using v8 bt) is not very useful, but this was expected and should be addressed by 2.

mmarchini

LGTM, the only thing I think we should change is on V8 and not on Node.js, so I'll open an upstream PR for that.

Edit: Upstream PR, if anyone is interested: https://chromium-review.googlesource.com/c/v8/v8/+/1518612

mhdawson

LGTM once the default behaviour is clarified.

BridgeAR · 2019-03-13T14:02:05Z

I improved the documentation and the warn I reworked the warn mode a tiny bit: it will now always warn (but without the deprecation notice), even if there is an unhandled rejections on in place.

The changes are in the 18c420d and a2eb1ea.

CI https://ci.nodejs.org/job/node-test-pull-request/21501/

benjamingr · 2019-03-13T14:03:59Z

@BridgeAR so to clarify, warn doesn't show the deprecation warning and it ignores handlers (assuming they don't actually handle the rejection) and the default did not change?

BridgeAR · 2019-03-13T14:16:31Z

@benjamingr

it ignores handlers

Exactly

assuming they don't actually handle the rejection

That's a good point. I forgot that they might actually add a handler. I'll add a fix for that so I verify that the promise is indeed still unhandled before printing the warning.

the default did not change

There is absolutely no behavior change if non of the flags is used. That is one of the goals with this PR.

BridgeAR · 2019-03-13T14:37:12Z

Thinking about it again: I would rather always warn, even if the unhandled rejection hook attached a handler. Otherwise it would a) be possible to silence those warnings with the hook which I think is orthogonal to what the user wants if they use the warn mode and b) it increases the complexity for the implementation (I have to wait another tick and add extra information and then check if it got handled in the meanwhile).

benjamingr

Explicit "still lgtm"

BridgeAR · 2019-03-13T14:56:08Z

CI https://ci.nodejs.org/job/node-test-pull-request/21504/

doc/api/cli.md

doc/api/process.md

BridgeAR · 2019-03-15T16:50:51Z

CI https://ci.nodejs.org/job/node-test-pull-request/21570/

@mmarchini @mcollina @mhdawson @benjamingr would you be so kind and confirm your LG? To me this seems ready to land.

ljharb

Still seems good to me!

Perhaps could this flag be set by an environment variable? That way it would be able to affect shebangs in files, or nested node commands i might not be able to edit.

This adds a flag to define the default behavior for unhandled rejections. Three modes exist: `none`, `warn` and `strict`. The first is going to silence all unhandled rejection warnings. The second behaves identical to the current default with the excetion that no deprecation warning will be printed and the last is going to throw an error for each unhandled rejection, just as regular exceptions do. It is possible to intercept those with the `uncaughtException` hook as with all other exceptions as well. This PR has no influence on the existing `unhandledRejection` hook. If that is used, it will continue to function as before. PR-URL: nodejs#26599 Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Matheus Marchini <mat@mmarchini.me> Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com> Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com> Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

This adds a flag to define the default behavior for unhandled rejections. Three modes exist: `none`, `warn` and `strict`. The first is going to silence all unhandled rejection warnings. The second behaves identical to the current default with the excetion that no deprecation warning will be printed and the last is going to throw an error for each unhandled rejection, just as regular exceptions do. It is possible to intercept those with the `uncaughtException` hook as with all other exceptions as well. This PR has no influence on the existing `unhandledRejection` hook. If that is used, it will continue to function as before. PR-URL: #26599 Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Matheus Marchini <mat@mmarchini.me> Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com> Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com> Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

Notable changes: * crypto: * add support for chacha20-poly1305 for AEAD (chux0519) #24081 * increase maxmem range from 32 to 53 bits (Tobias Nießen) #28799 * deps: * update npm to 6.11.3 (claudiahdz) #29430 * upgrade openssl sources to 1.1.1d (Sam Roberts) #29921 * dns: * remove dns.promises experimental warning (cjihrig) #26592 * fs: * remove experimental warning for fs.promises (Anna Henningsen) #26581 * http: * makes response.writeHead return the response (Mark S. Everitt) #25974 * http2: * makes response.writeHead return the response (Mark S. Everitt) #25974 * n-api: * make func argument of napi\_create\_threadsafe\_function optional (legendecas) #27791 * mark version 5 N-APIs as stable (Gabriel Schulhof) #29401 * implement date object (Jarrod Connolly) #25917 * process: * add --unhandled-rejections flag (Ruben Bridgewater) #26599 * stream: * implement Readable.from async iterator utility (Guy Bedford) #27660 * make Symbol.asyncIterator support stable (Matteo Collina) #26989 PR-URL: #29875

--unhandled-rejections has three explicit modes (strict, warn, none) plus one implicit "default" mode, which logs an additional deprecation warning (DEP0018). Prior to this commit, the default mode was subtly different from warn mode. If the unhandledRejections hook is set, default mode suppresses all warnings. In warn mode, unhandledRejections would always fire a warning, regardless of whether the hook was set. In addition, prior to this commit, strict mode would always throw an exception, regardless of whether the hook was set. In this commit, all modes honor the unhandledRejections hook. If the user has set the hook, then the user has taken full responsibility over the behavior of unhandled rejections. In that case, no additional warnings or thrown exceptions will be fired, even in warn mode or strict mode. This commit is a stepping stone towards resolving DEP0018. After this commit, any code that includes an unhandledRejection hook will behave unchanged when we change the default mode. Refs: nodejs#26599

BridgeAR added the semver-minor PRs that contain new features and should be released in the next minor version. label Mar 11, 2019

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src: exit on gc unhandled rejection #20097

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v10.16.0 proposal #27514

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[v10.x] backport #26599 (process: add --unhandled-rejections flag) #29036

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v10.17.0 proposal #29875

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himself65 mentioned this pull request Apr 13, 2020

misleading command line help docs for "unhandled-rejections=mode" in "node --help server" #32796

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process: Don't warn/throw on unhandled rejections when hook is set #33017

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