domain: avoid circular memory references #25993

addaleax · 2019-02-07T20:25:46Z

src: add WeakReference utility

Add a simple WeakReference utility that we can use until the
language provides something on its own.

domain: avoid circular memory references

Avoid circular references that the JS engine cannot see through
because it involves an async id ⇒ domain link.

Using weak references is not a great solution, because it increases
the domain module’s dependency on internals and the added calls into
C++ may affect performance, but it seems like the least bad one.

Fixes: #23862

Checklist

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

Add a simple `WeakReference` utility that we can use until the language provides something on its own.

Avoid circular references that the JS engine cannot see through because it involves an `async id` ⇒ `domain` link. Using weak references is not a great solution, because it increases the domain module’s dependency on internals and the added calls into C++ may affect performance, but it seems like the least bad one. Fixes: nodejs#23862

nodejs-github-bot · 2019-02-07T20:25:48Z

@addaleax build started: https://ci.nodejs.org/blue/organizations/jenkins/node-test-pull-request-lite-pipeline/detail/node-test-pull-request-lite-pipeline/2539/pipeline

ChALkeR · 2019-02-07T20:33:15Z

This approach looks fine to me, given the current situation.

How does the memory profile for this look like? E.g., taken the example from #23862 as-is, and hammering it with GET requests, how high would the memory usage be with and without domains usage on the server side?

mcollina

LGTM as much as I don't like it. At least it fixes a bad bug.

addaleax · 2019-02-07T20:48:35Z

@ChALkeR What I’m getting is about 8 kB per request with that example before this patch, and flat memory usage afterwards.

ChALkeR · 2019-02-07T21:34:36Z

@addaleax

and flat memory usage afterwards.

That is what I was expecting, but I was curious about the exact memory usage profile with/without domains code on the server logic side (with this patch enabled) for the same requests pattern.

Anyway, this change looks good to me in approach and code-wise. I have not tested this locally (yet?), but this should be good once CI passes.

src/node_util.cc

refack

I'm not sure I understand the API of WeakReference. Could you write a cctest for it?

lib/domain.js

addaleax · 2019-02-07T23:12:06Z

Could you write a cctest for it?

I don’t think a cctest makes sense, but I could write a regular test if you feel that it’s important.

refack · 2019-02-07T23:56:48Z

I could write a regular test if you feel that it’s important.

If we want to reuse this is other code path I think we should cover the API.

vdeturckheim

LGTM. Technically this would mean that CLS-like implementation based on Async Hooks should be rewriten ovev domain as there is no mem leak anymore here.

addaleax · 2019-02-08T13:07:55Z

I could write a regular test if you feel that it’s important.

If we want to reuse this is other code path I think we should cover the API.

@refack I think we want to avoid that as much as possible. I’ve added a test, though.

LGTM. Technically this would mean that CLS-like implementation based on Async Hooks should be rewriten ovev domain as there is no mem leak anymore here.

@vdeturckheim No, that’s not necessarily true. The problem here is specific to domains, because they (needlessly?) keep references to objects that they track.

Ideally, we’d revert this change and remove domain.members – I’ll propose this once this PR lands, but I think it would be semver-major.

addaleax · 2019-02-08T13:09:27Z

(That’s doesn’t mean that it’s not easy to run into memory leaks when using async_hooks, but that’s a fundamental design flaw and a much bigger issue.)

bnoordhuis · 2019-02-08T15:08:49Z

lib/domain.js

@@ -53,20 +57,22 @@ const asyncHook = createHook({
  init(asyncId, type, triggerAsyncId, resource) {
    if (process.domain !== null && process.domain !== undefined) {
      // If this operation is created while in a domain, let's mark it
-      pairing.set(asyncId, process.domain);
+      pairing.set(asyncId, process.domain[kWeak]);


Is it conceivable that user code tampers with process.domain?

What would happen if I set process.domain = {}?

I don’t think the domain code is all that tampering-proof to being with…

I’m also not sure what we could do in that case.

bnoordhuis · 2019-02-08T15:15:02Z

src/node_util.cc

+  static void Get(const FunctionCallbackInfo<Value>& args) {
+    WeakReference* weak_ref = Unwrap<WeakReference>(args.Holder());
+    Isolate* isolate = args.GetIsolate();
+    if (!weak_ref->target_.IsEmpty())


Technically not necessary: Persistent<T>::Get() will return an empty handle, causing ReturnValue<T>::Set() to default to undefined.

Thought about it, and I think I’d prefer an explicit variant here, so that it’s a bit more obvious what happens when the object has been GC’ed…

refack · 2019-02-08T17:04:09Z

CI: https://ci.nodejs.org/job/node-test-pull-request/20674/

addaleax · 2019-02-12T00:16:38Z

Resume CI: https://ci.nodejs.org/job/node-test-pull-request/20735/

Add a simple `WeakReference` utility that we can use until the language provides something on its own. PR-URL: #25993 Fixes: #23862 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de> Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com> Reviewed-By: Vladimir de Turckheim <vlad2t@hotmail.com> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Refael Ackermann <refack@gmail.com>

Avoid circular references that the JS engine cannot see through because it involves an `async id` ⇒ `domain` link. Using weak references is not a great solution, because it increases the domain module’s dependency on internals and the added calls into C++ may affect performance, but it seems like the least bad one. PR-URL: #25993 Fixes: #23862 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de> Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com> Reviewed-By: Vladimir de Turckheim <vlad2t@hotmail.com> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Refael Ackermann <refack@gmail.com>

avaly · 2019-02-15T08:53:06Z

Is this fix planned to be back-ported to the v10 release?

abraxxas · 2019-03-25T10:07:15Z

Any update if this will be backported to LTS?

Add a simple `WeakReference` utility that we can use until the language provides something on its own. PR-URL: nodejs#25993 Fixes: nodejs#23862 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de> Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com> Reviewed-By: Vladimir de Turckheim <vlad2t@hotmail.com> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Refael Ackermann <refack@gmail.com>

Avoid circular references that the JS engine cannot see through because it involves an `async id` ⇒ `domain` link. Using weak references is not a great solution, because it increases the domain module’s dependency on internals and the added calls into C++ may affect performance, but it seems like the least bad one. PR-URL: nodejs#25993 Fixes: nodejs#23862 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de> Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com> Reviewed-By: Vladimir de Turckheim <vlad2t@hotmail.com> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Refael Ackermann <refack@gmail.com>

MylesBorins · 2019-05-17T15:45:54Z

Backport opened in #27749

Add a simple `WeakReference` utility that we can use until the language provides something on its own. Backport-PR-URL: #27749 PR-URL: #25993 Fixes: #23862 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de> Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com> Reviewed-By: Vladimir de Turckheim <vlad2t@hotmail.com> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Refael Ackermann <refack@gmail.com>

Avoid circular references that the JS engine cannot see through because it involves an `async id` ⇒ `domain` link. Using weak references is not a great solution, because it increases the domain module’s dependency on internals and the added calls into C++ may affect performance, but it seems like the least bad one. Backport-PR-URL: #27749 PR-URL: #25993 Fixes: #23862 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de> Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com> Reviewed-By: Vladimir de Turckheim <vlad2t@hotmail.com> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Refael Ackermann <refack@gmail.com>

addaleax added 2 commits February 7, 2019 21:25

src: add WeakReference utility

ebaae77

Add a simple `WeakReference` utility that we can use until the language provides something on its own.

nodejs-github-bot added c++ Issues and PRs that require attention from people who are familiar with C++. domain Issues and PRs related to the domain subsystem. util Issues and PRs related to the built-in util module. labels Feb 7, 2019

addaleax mentioned this pull request Feb 7, 2019

Memory leak when a Promise is stored on an Express request that's added to a domain #23862

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addaleax added 2 commits February 8, 2019 14:03

fixup! src: add WeakReference utility

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fixup! domain: avoid circular memory references

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addaleax deleted the domain-leak branch February 12, 2019 20:13

garthenweb mentioned this pull request Feb 13, 2019

@sentry/node memory leaks on node 10.13.0 getsentry/sentry-javascript#1762

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v11.10.0 proposal #26098

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v10.15.3 proposal #26063

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Memory leak in Valetudo? Hypfer/Valetudo#39

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v10.16.0 proposal #27514

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[v10.x] domain: avoid circular memory references #27749

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