src: use symbol to store `AsyncWrap` resource by addaleax · Pull Request #31745 · nodejs/node

addaleax · 2020-02-12T00:26:43Z

Use a symbol on the bindings object to store the public resource object,
rather than a v8::Global Persistent. This has several advantages:

It’s harder to inadvertently create memory leaks this way.
The garbage collector sees the AsyncWrap → resource link like
a regular JS property, and can collect the objects as a group,
even if the resource object should happen to point back to the
AsyncWrap object.
This will make it easier in the future to use owner_symbol for
this purpose, which is generally the direction we should be moving
the async_hooks API into (i.e. using more public objects instead
of letting internal wires stick out).

Checklist

make -j4 test (UNIX), or vcbuild test (Windows) passes
commit message follows commit guidelines

lib/internal/async_hooks.js

nodejs-github-bot · 2020-02-13T20:03:32Z

CI: https://ci.nodejs.org/job/node-test-pull-request/29108/

nodejs-github-bot · 2020-02-23T02:28:46Z

CI: https://ci.nodejs.org/job/node-test-pull-request/29290/

nodejs-github-bot · 2020-02-26T03:31:59Z

CI: https://ci.nodejs.org/job/node-test-pull-request/29364/

addaleax · 2020-02-26T18:55:41Z

Looks like un-setting the field during GC isn’t allowed (which is reasonable, I guess). I’ll switch this over to using an internal field after #31960 lands – that should work as well. The big downside there is that it will make merging with owner_symbol harder, not easier.

Use a symbol on the bindings object to store the public resource object, rather than a `v8::Global` Persistent. This has several advantages: - It’s harder to inadvertently create memory leaks this way. The garbage collector sees the `AsyncWrap` → resource link like a regular JS property, and can collect the objects as a group, even if the resource object should happen to point back to the `AsyncWrap` object. - This will make it easier in the future to use `owner_symbol` for this purpose, which is generally the direction we should be moving the `async_hooks` API into (i.e. using more public objects instead of letting internal wires stick out).

addaleax · 2020-05-19T16:58:08Z

I’ve rebased this, with a smaller patch that instead only unsets the resource if not triggered from GC. I think that’s fine, considering that the object won’t be accessed anymore anyway if EmitDestroy() is caued by GC, and it’s more in line with the original intention of the PR, which included making this more similar to owner_symbol.

nodejs-github-bot · 2020-05-19T16:58:58Z

CI: https://ci.nodejs.org/job/node-test-pull-request/31415/

Qard

LGTM, with one non-blocking question.

src/async_wrap.cc

nodejs-github-bot · 2020-05-20T10:31:16Z

CI: https://ci.nodejs.org/job/node-test-pull-request/31437/

jasnell · 2020-05-22T00:43:56Z

src/async_wrap.h

  static void EmitPromiseResolve(Environment* env, double async_id);

-  void EmitDestroy();
+  void EmitDestroy(bool from_gc = false);


non-blocking nit... would prefer an enum here rather than a bool but that can be done in a separate PR

I generally agree with that but here there’s effectively only one call site where passing true ever makes sense, so I don’t think this really falls under “boolean trap”.

Use a symbol on the bindings object to store the public resource object, rather than a `v8::Global` Persistent. This has several advantages: - It’s harder to inadvertently create memory leaks this way. The garbage collector sees the `AsyncWrap` → resource link like a regular JS property, and can collect the objects as a group, even if the resource object should happen to point back to the `AsyncWrap` object. - This will make it easier in the future to use `owner_symbol` for this purpose, which is generally the direction we should be moving the `async_hooks` API into (i.e. using more public objects instead of letting internal wires stick out). PR-URL: #31745 Reviewed-By: Stephen Belanger <admin@stephenbelanger.com> Reviewed-By: David Carlier <devnexen@gmail.com> Reviewed-By: Denys Otrishko <shishugi@gmail.com> Reviewed-By: Chengzhong Wu <legendecas@gmail.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Minwoo Jung <nodecorelab@gmail.com> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com> Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>

jasnell · 2020-05-22T00:46:23Z

Landed in 6f6bf01

Use a symbol on the bindings object to store the public resource object, rather than a `v8::Global` Persistent. This has several advantages: - It’s harder to inadvertently create memory leaks this way. The garbage collector sees the `AsyncWrap` → resource link like a regular JS property, and can collect the objects as a group, even if the resource object should happen to point back to the `AsyncWrap` object. - This will make it easier in the future to use `owner_symbol` for this purpose, which is generally the direction we should be moving the `async_hooks` API into (i.e. using more public objects instead of letting internal wires stick out). PR-URL: #31745 Reviewed-By: Stephen Belanger <admin@stephenbelanger.com> Reviewed-By: David Carlier <devnexen@gmail.com> Reviewed-By: Denys Otrishko <shishugi@gmail.com> Reviewed-By: Chengzhong Wu <legendecas@gmail.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Minwoo Jung <nodecorelab@gmail.com> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com> Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>

Use a symbol on the bindings object to store the public resource object, rather than a `v8::Global` Persistent. This has several advantages: - It’s harder to inadvertently create memory leaks this way. The garbage collector sees the `AsyncWrap` → resource link like a regular JS property, and can collect the objects as a group, even if the resource object should happen to point back to the `AsyncWrap` object. - This will make it easier in the future to use `owner_symbol` for this purpose, which is generally the direction we should be moving the `async_hooks` API into (i.e. using more public objects instead of letting internal wires stick out). PR-URL: nodejs#31745 Reviewed-By: Stephen Belanger <admin@stephenbelanger.com> Reviewed-By: David Carlier <devnexen@gmail.com> Reviewed-By: Denys Otrishko <shishugi@gmail.com> Reviewed-By: Chengzhong Wu <legendecas@gmail.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Minwoo Jung <nodecorelab@gmail.com> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com> Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>

Use a symbol on the bindings object to store the public resource object, rather than a `v8::Global` Persistent. This has several advantages: - It’s harder to inadvertently create memory leaks this way. The garbage collector sees the `AsyncWrap` → resource link like a regular JS property, and can collect the objects as a group, even if the resource object should happen to point back to the `AsyncWrap` object. - This will make it easier in the future to use `owner_symbol` for this purpose, which is generally the direction we should be moving the `async_hooks` API into (i.e. using more public objects instead of letting internal wires stick out). PR-URL: #31745 Backport-PR-URL: #33962 Reviewed-By: Stephen Belanger <admin@stephenbelanger.com> Reviewed-By: David Carlier <devnexen@gmail.com> Reviewed-By: Denys Otrishko <shishugi@gmail.com> Reviewed-By: Chengzhong Wu <legendecas@gmail.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Minwoo Jung <nodecorelab@gmail.com> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com> Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>

Notable changes: - deps: V8: backport fb26d0bb1835 (Matheus Marchini) [#33573](#33573) - src: use symbol to store `AsyncWrap` resource (Anna Henningsen) [#31745](#31745) PR-URL: TBD

Notable changes: - deps: V8: backport fb26d0bb1835 (Matheus Marchini) [#33573](#33573) - src: use symbol to store `AsyncWrap` resource (Anna Henningsen) [#31745](#31745) PR-URL: #34077

MylesBorins · 2020-07-21T20:14:45Z

This change landing on v12.18.2 resulted in breakages in the glob-watcher module being used internally by gulp. The breakages appear to be related to an out of date dependency on chokidar which in turn depends on an out of date version of fsevents. While this did break in a semver-patch, it is not clear that this specific change caused the breakage as opposed to making an existing breakage more obvious by fixing something else.

At the moment I don't think there is any need to revert, but wanted to document research here.

Flarna · 2020-08-20T08:11:38Z

Refs: #30959

It's somehow a followup and fixed an issue introduced so keep them linked.

addaleax requested a review from Qard February 12, 2020 00:26

nodejs-github-bot added c++ Issues and PRs that require attention from people who are familiar with C++. lib / src Issues and PRs related to general changes in the lib or src directory. labels Feb 12, 2020

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Investigate flaky test-http2-ping-settings-heapdump #31962

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addaleax mentioned this pull request May 19, 2020

TLSWrap objects grow with HTTP keep-alive enabled until out of memory error occurs #33468

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addaleax added 2 commits May 19, 2020 14:56

fixup! src: use symbol to store AsyncWrap resource

a6b337d

addaleax force-pushed the async-hooks-resource-symbol branch from 64ce34f to a6b337d Compare May 19, 2020 16:26

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addaleax deleted the async-hooks-resource-symbol branch June 19, 2020 13:47

addaleax mentioned this pull request Jun 19, 2020

[v12.x] src: use symbol to store AsyncWrap resource #33962

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v12.18.2 proposal #34077

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v14.5.0 proposal #34093

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deps: V8: cherry-pick eec10a2fd8fa #33778

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addaleax added backported-to-v12.x and removed backport-open-v12.x labels Sep 23, 2020

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