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lib,src: "throw" on unhandled promise rejections #6375

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lib,src: "throw" on unhandled promise rejections #6375

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Fishrock123
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@Fishrock123 Fishrock123 commented Apr 25, 2016 •
edited by estliberitas
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Checklist
  • tests and code linting passes
  • a test and/or benchmark is included
  • documentation is changed or added
  • the commit message follows commit guidelines
Affected core subsystem(s)

promises or something

Description of change

Refs: #5292
Refs: nodejs/promises#26
Refs: #6355

Makes Promises "throw" rejections which exit like regular uncaught errors. However, it only happens if:

  • An unhandled promise is GC'd
  • Unhandled promises are not handled by the time the process exits normally.

Please take a look @nodejs/ctc @nodejs/promises @benjamingr @chrisdickinson etc

@Fishrock123 Fishrock123 added semver-major PRs that contain breaking changes and should be released in the next major version. lib / src Issues and PRs related to general changes in the lib or src directory. labels Apr 25, 2016
@Fishrock123 Fishrock123 added this to the 6.0.0 milestone Apr 25, 2016
@nodejs-github-bot nodejs-github-bot added the c++ Issues and PRs that require attention from people who are familiar with C++. label Apr 25, 2016
This was referenced Apr 25, 2016
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For background on why, please see nodejs/promises#26 (comment)

CI: https://ci.nodejs.org/job/node-test-pull-request/2385/

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Fishrock123 commented Apr 25, 2016 •
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Ugh a rebase screwed up. I'll deal with it later

indutny
indutny reviewed Apr 25, 2016
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tools/test.py Outdated
@@ -1527,6 +1527,7 @@ def Main():
vmArch = archEngineContext.stdout.rstrip()
if archEngineContext.exit_code is not 0 or vmArch == "undefined":
print "Can't determine the arch of: '%s'" % vm
print archEngineContext.stderr.rstrip()
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Rationale behind this?

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Should be in a separate PR. Sometimes the test runner will swallow startup errors here.

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Ugh, guess I rebased onto a newer v8, now all the WeakCallback stuff is broken... 😞

../src/track-promise.cc:35:29: error: reference to non-static member function must be called
  persistent_.SetWeak(this, WeakCallback);
                            ^~~~~~~~~~~~
../src/track-promise.h:20:15: note: possible target for call
  inline void WeakCallback(
              ^
../src/track-promise.h:24:15: note: possible target for call
  inline void WeakCallback(v8::Isolate* isolate, v8::Local<v8::Object> object);
              ^
1 error generated.

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@Fishrock123 Don’t think so… If I read this correctly, the compiler is right, TrackPromise::WeakCallback(const WeakCallbackData<Object, TrackPromise>& data) should be static?

ofrobots
ofrobots reviewed Apr 25, 2016
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src/track-promise.cc Outdated

void TrackPromise::WeakCallback(
const WeakCallbackData<Object, TrackPromise>& data) {
data.GetParameter()->WeakCallback(data.GetIsolate(), data.GetValue());
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You're using the deprecated SetWeak API. In the non-deprecated version, the weak object is already garbage collected by the time the weak callback gets called. In other words, you won't be able to get your hands onto the promise object in the weak callback.

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I have word that this won't actually be removed remotely soon?

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@ofrobots ofrobots Apr 25, 2016 •
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I would strongly encourage you to use the new SetWeak API to make sure this feature is implementable on top of the new API. The old APIs have been deprecated for a long time switched over to imminently deprecated in V8 4.9. /cc @jeisinger.

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@ofrobots You just said this isn't possible with that API though?

I need access to the promise "reason", at very least in an associable way to storage of the "reason" (the object that is rejected).

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Is it possible for you to get and save the promise reason before the weak callback gets invoked? If so, this should be implementable using the new API.

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@ofrobots ofrobots Apr 25, 2016 •
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Basically, at the time you need to create the TrackPromise object, you need to keep a reference to the reason in the TrackPromise object. Later when the weak callback gets called, you should look up the reason object you hold in the TrackPromise C++ object rather than depending upon the promise object being available.

The other thing you will need to ensure (@jeisinger may know this off the top of his head) is that the reason object doesn't hold a reference to the promise.

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I hacked a quick patch to switch you over to the new SetWeak API: ofrobots@d1e98e8

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btw, I added WeakCallbackType::kFinalizer to the WeakCallbackInfo<> API to preserve the old behavior here https://codereview.chromium.org/1883173002

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@nodejs/v8 Looks like this old API was removed, could someone point me to how to use the new replacement API? If it is easier to guide me on something like IRC that would totally work too. (Sorry C++ are very rusty!)

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I don't have too much context on the PR but this patch https://github.com/matthewloring/node/commit/f740100758db9de6d20531feba7e512d64a54f37 should get things compiling again.

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@addaleax Interesting... seems to work, I don't really understand why though.

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New CI: https://ci.nodejs.org/job/node-test-pull-request/2387/

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@Fishrock123 When you use a non-static WeakCallback, it would like to have a this object it can refer to when it’s being executed, and C++ doesn’t allow this (in a simple way). https://isocpp.org/wiki/faq/pointers-to-members explains this quite extensively, if you’re interested.

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Fishrock123 commented Apr 25, 2016 •
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Updated, nits addressed, more tests added, CI: https://ci.nodejs.org/job/node-test-pull-request/2390/

Fixed more stuff: https://ci.nodejs.org/job/node-test-pull-request/2391/

@Fishrock123 Fishrock123 force-pushed the promise-unhandled-default branch 2 times, most recently from 55a3103 to 7e2a08c Compare April 25, 2016 21:33
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Also, is this really semver-major? It would make my life significantly easier if it wasn't.

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jasnell commented Apr 25, 2016

The change itself seems fine to me but I'll leave the sign off to others who know the details of Promises and uncaught exceptions more than I do. Given the likelihood that this will break existing code that depend on the rejections being swallowed, I'm hesitant to make this anything but major. I'm also hesitant on landing this so soon before cutting v6. But I certainly won't object if @nodejs/CTC are +1

@Fishrock123 Fishrock123 mentioned this pull request Apr 25, 2016
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@Fishrock123 Fishrock123 changed the title lib,src: throw on unhanded promise rejections lib,src: "throw" on unhanded promise rejections Apr 26, 2016
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ping again @nodejs/v8 - can anyone help me with issues related to the new WeakCallbackInfo API and not receiving notification on GC from it?

I'd really like to at least have this working properly again before I open up a new PR for visibility.

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@Fishrock123 What is the question?

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@bnoordhuis Either: why the new API doesn't fire the WeakCallbackInfo event/handle/callback at GC, or, why GC doesn't happen for promises here.

test/message/reject_promise.js is the example test that does not work correctly, and the relevant tracking code is all in src/track_promise.cc.

@LewisJEllis LewisJEllis mentioned this pull request Jan 26, 2017
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I can take a look soon. FWIW in v8's debugger we also have an event for when the promise has been collected, also building on top of weak handles. Look in src/debug/debug.cc for SendAsyncTaskEventCancel.

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Look in src/debug/debug.cc for SendAsyncTaskEventCancel.

Sorry, I really don't understand what is going on there. :(

@addaleax addaleax self-requested a review February 28, 2017 22:41
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addaleax commented Mar 1, 2017

@Fishrock123 a6a36a5...21e5bb5 works and you can pull it in here if you like the approach (if you do please remove my debug code 😄)

@Timer Timer mentioned this pull request Mar 13, 2017
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Closing this in favor of opening a new pull request. Will link shortly.

@Fishrock123 Fishrock123 mentioned this pull request Mar 23, 2017
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I have filed a new pull request at #12010, if you are still interested or against this, please go there.

Fishrock123 added a commit to Fishrock123/node that referenced this pull request Apr 28, 2017
@Fishrock123
lib,src: throw on unhanded promise rejections
1f9635d 
Refs: nodejs#5292
Refs: nodejs/promises#26
Refs: nodejs#6355
PR-URL: nodejs#6375
Fishrock123 added a commit to Fishrock123/node that referenced this pull request Apr 28, 2017
@Fishrock123
lib,src: throw on unhanded promise rejections
f6e35fe 
Refs: nodejs#12010
Refs: nodejs#5292
Refs: nodejs/promises#26
Refs: nodejs#6355
PR-URL: nodejs#6375
@Fishrock123 Fishrock123 mentioned this pull request Apr 28, 2017
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BridgeAR pushed a commit to BridgeAR/node that referenced this pull request Sep 26, 2017
@Fishrock123 @BridgeAR
lib,src: throw on unhanded promise rejections
711d699 
src: use std::map for the promise reject map

Refs: nodejs#5292
Refs: nodejs/promises#26
Refs: nodejs#6355
Refs: nodejs#6375
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