events: unwrap #once listeners in #listeners #6881

omsmith · 2016-05-19T15:56:47Z

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)

events

Description of change

Fixes: #6873

cjihrig · 2016-05-19T16:10:59Z

lib/events.js

@@ -425,9 +425,9 @@ EventEmitter.prototype.listeners = function listeners(type) {
    if (!evlistener)
      ret = [];
    else if (typeof evlistener === 'function')
-      ret = [evlistener];
+      ret = [evlistener.listener ? evlistener.listener : evlistener];


Could you just do evlistener.listener || evlistener?

Sure thing, pushing that up. This was just mirroring the check as written for 'newListener'.

cjihrig · 2016-05-19T16:12:32Z

LGTM with a couple comments.

addaleax · 2016-05-19T17:19:06Z

lib/events.js

@@ -475,3 +475,11 @@ function arrayClone(arr, i) {
    copy[i] = arr[i];
  return copy;
 }
+
+function unwrapListeners(arr) {
+  var ret = new Array(arr.length);


nit: const?

addaleax · 2016-05-19T17:21:48Z

LGTM with a nit… #5564 was labelled as semver-major. What do you think?

cjihrig · 2016-05-19T17:29:14Z

#6394 got through as a patch, so it could probably go either way. It just depends if we want to look at this as a bug or not.

jasnell · 2016-05-19T17:39:20Z

I call bug.

jasnell · 2016-05-19T17:39:58Z

LGTM if CI is green and @addaleax' nit is addressed.

Fixes: nodejs#6873

omsmith · 2016-05-19T17:49:46Z

Updated with const

addaleax · 2016-05-22T14:17:52Z

CI: https://ci.nodejs.org/job/node-test-commit/3436/

Going to land this if it’s green.

Fishrock123 · 2016-05-22T14:26:45Z

Should we run citgm against this? I don't understand whether or not there is risk here.

Edit: here's a run regardless: https://ci.nodejs.org/view/Node.js-citgm/job/thealphanerd-smoker/277/

jasnell · 2016-05-22T16:09:39Z

Couple of citgm failures on ubuntu ppc -> https://ci.nodejs.org/view/Node.js-citgm/job/thealphanerd-smoker/277/nodes=ppcle-ubuntu1404/tapTestReport/

addaleax · 2016-05-22T16:32:02Z

Nothing that looks related… @Fishrock123 is it okay for you to consider this a semver-patch one?

Fishrock123 · 2016-05-22T17:58:58Z

I don't have a firm opinion. If you are confident about it, go ahead. :)

addaleax · 2016-05-22T19:02:32Z

The more I think about this the more I start to get cautious… e.g. I didn’t realize this so far, but I’d be creating a bug myself in #6635 if this one landed, too, because I was assuming that re-adding the elements from listeners() using .addListener() would restore the previous situation.

So, eh, thanks for making me think twice…

addaleax · 2016-05-22T19:37:42Z

i.e. there’s a valid use case for the old behaviour, namely temporarily disabling listeners by storing the result of listeners(), removing all of them and re-attaching them later.

ChALkeR · 2016-05-23T09:41:51Z

This was discussed before in #914, will break several modules, and is clearly a semver-major.
Also related: #5127.

See https://github.com/timoxley/overshadow-listeners/blob/master/index.js, for example.

addaleax · 2016-05-23T10:29:55Z

Could we add an option to .listeners() that defaults to the current behaviour of returning unwrapped listeners to un-semver-major this? Changing the that default could still be discussed as a separate semver-major change…

jasnell · 2016-05-23T13:30:36Z

I view this one as a bug fix and would rather the default behavior be to
return the unwrapped listeners. Mark it semver-major if necessary but the
current behavior is broken.
On May 23, 2016 3:30 AM, "Anna Henningsen" [email protected] wrote:

Could we add an option to .listeners() that defaults to the current
behaviour of returning unwrapped listeners to un-semver-major this?
Changing the that default could still be discussed as a separate
semver-major change…

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#6881 (comment)

ChALkeR · 2016-05-23T13:48:22Z

@jasnell It looks like there will be no way to re-attach the events then, which could be useful for cloning, intercepting, or temporary disabling events. Perhaps some API should be added that allows that?

Edit: obviously missed «no» here, updated.

addaleax · 2016-05-27T23:35:37Z

Concrete proposal for implementation as an optional feature: addaleax/node@cd0a542310be. What do you think?

Fishrock123 · 2016-05-28T02:29:49Z

Could someone clarify for myself and anyone else who may drop in here what we mean by "unwrapping"? Thanks!

addaleax · 2016-05-28T02:41:37Z

@Fishrock123 oh, sorry, wasn’t aware that this isn’t clear here (and that also means that we probably need a better name). So, I hope the following sums up everything so far:

Basically, .once() uses .on() internally, but wraps the user-supplied function using a closure that, when invoked, first removes itself from the event listener list and then calls the original user-supplied function. This closure has a .listener property that refers to that original function.

Unwrapping refers to returning the .listener property of an event handler, if present, when e.g. emitter.listeners() is called; it makes sense to do that from one perspective, because those are the values that the user actually supplied to .on()/.once(), and they can’t really use the wrapped listeners themselves.

For example, in

const emitter = new EventEmitter();
function listener() {}
emitter.once('foo', listener);
emitter.listeners('foo')[0] === listener // this should be true? no?
emitter.listeners('foo')[0].listener === listener // this is currently true, but not documented in any way

it would probably reflect user expectations to return the original listener function in emitter.listeners('foo')[0].

Fishrock123 · 2016-05-28T14:49:45Z

Basically, .once() uses .on() internally, but wraps the user-supplied function using a closure that, when invoked, first removes itself from the event listener list and then calls the original user-supplied function.

Ah right, I totally knew that but didn't link the two... >_<

jasnell · 2016-08-05T22:56:15Z

@nodejs/ctc ... looks like this one fell by the way side accidentally. Please take a moment to review (again if you already reviewed it once).

jasnell · 2016-08-05T22:56:37Z

LGTM if CI is green.
CI: https://ci.nodejs.org/job/node-test-pull-request/3547/

mscdex · 2016-08-05T23:03:55Z

citgm again: https://ci.nodejs.org/view/Node.js-citgm/job/citgm-smoker/345/

yorkie · 2016-08-06T02:34:20Z

lib/events.js

    else
-      ret = arrayClone(evlistener, evlistener.length);


Should we remove the arrayClone function and do replace all arrayClone() to unwrapListeners()?

No, the other usages of arrayClone expect the wrapped listeners.

However I think the only difference between is that arrayClone supports a copy with a specified length, 2nd argument and the assignment from .listener of elements.

The function upwrapListeners seems to be only used inside to EE.prototype.listeners, so could we declare this function inside the prototype method to be unwrap? Both the functions defined at bottom looks like those pure collection ones.

I would expect declaring unwrapListeners within listeners (I believe that's what you're suggesting?) to result in a performance degradation.

jasnell · 2016-08-09T21:12:14Z

CI is green and CITGM is only showing known flaky failures. Will get this landed.
If there's anything additional that needs to be done here, we can do a follow on PR

Fixes: #6873 PR-URL: #6881 Reviewed-By: Colin Ihrig <[email protected]> Reviewed-By: Anna Henningsen <[email protected]> Reviewed-By: James M Snell <[email protected]>

jasnell · 2016-08-09T21:15:00Z

Landed in b7a8a69! (finally ;-) ...)

Matches the Node 8 API. v1 matched Node 4, and some new methods have since been introduced (notably `prepend[Once]Listener`). The major bump in `events` was because: - There is a breaking change in the `listeners()` method regarding `once()` listeners nodejs/node#6881 I think it's super unlikely to affect anyone, but there you go. - The gzipped size almost doubled from 1.1KB to 2.1KB. It'll shrink a bit because some patches have since landed in Node that remove some code, but it'll still be bigger than it was because of the new methods. Deets: https://github.com/Gozala/events/releases/tag/v2.0.0

nodejs-github-bot added the events Issues and PRs related to the events subsystem / EventEmitter. label May 19, 2016

cjihrig reviewed May 19, 2016
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omsmith force-pushed the events-listeners-fix-once-unwrapping branch from 49951dc to 3b2551a Compare May 19, 2016 16:48

addaleax reviewed May 19, 2016
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events: unwrap #once listeners in #listeners

d667704

Fixes: nodejs#6873

omsmith force-pushed the events-listeners-fix-once-unwrapping branch from 3b2551a to d667704 Compare May 19, 2016 17:49

ChALkeR added the semver-major PRs that contain breaking changes and should be released in the next major version. label May 23, 2016

addaleax mentioned this pull request Jun 6, 2016

events: allow unwraping #once handler in listeners #7172

Closed

4 tasks

addaleax mentioned this pull request Jun 9, 2016

vm,repl: (add ability to) break on sigint/ctrl+c #6635

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yorkie reviewed Aug 6, 2016
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jasnell pushed a commit that referenced this pull request Aug 9, 2016

events: unwrap #once listeners in #listeners

b7a8a69

Fixes: #6873 PR-URL: #6881 Reviewed-By: Colin Ihrig <[email protected]> Reviewed-By: Anna Henningsen <[email protected]> Reviewed-By: James M Snell <[email protected]>

jasnell closed this Aug 9, 2016

gibfahn mentioned this pull request Jun 15, 2017

Auditing for 6.11.1 nodejs/Release#230

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3 tasks

loppear mentioned this pull request Nov 27, 2017

Fix issue with node event listeners change nxus/core#117

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apapirovski mentioned this pull request Dec 3, 2017

events: remove reaches into _events internals #17440

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goto-bus-stop mentioned this pull request Feb 15, 2018

Update events to v3 webpack/node-libs-browser#74

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events: unwrap #once listeners in #listeners #6881

events: unwrap #once listeners in #listeners #6881

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events: unwrap #once listeners in #listeners #6881

events: unwrap #once listeners in #listeners #6881

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omsmith commented May 19, 2016

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