src: keep main-thread Isolate attached to platform during Dispose #31795

addaleax · 2020-02-14T15:33:17Z

This works around a situation in which the V8 WASM code calls
into the platform while the Isolate is being disposed.

This goes against the V8 API constract for v8::Platform.
In lieu of a proper fix, it should be okay to keep the Isolate
registered; the race condition fixed by 25447d8 cannot
occur for the NodeMainInstance’s Isolate, as it is the last
one to exit in any given Node.js process.

This partially reverts 25447d8.

Refs: #30909
Refs: #31752

Checklist

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

This works around a situation in which the V8 WASM code calls into the platform while the Isolate is being disposed. This goes against the V8 API constract for `v8::Platform`. In lieu of a proper fix, it should be okay to keep the Isolate registered; the race condition fixed by 25447d8 cannot occur for the `NodeMainInstance`’s Isolate, as it is the last one to exit in any given Node.js process. This partially reverts 25447d8. Refs: nodejs#30909 Refs: nodejs#31752

nodejs-github-bot · 2020-02-14T15:34:05Z

CI: https://ci.nodejs.org/job/node-test-pull-request/29131/

addaleax · 2020-02-14T15:34:23Z

Please 👍 to fast-track this for inclusion in #31781 (v12.16.1).

jasnell

LGTM as a temporary fix but I definitely worry about breaking the contract here. Do we know what the WASM edge cases are and is there a better way of working around those?

addaleax · 2020-02-14T16:14:28Z

@jasnell I don’t have a full understanding of the situation yet. It looks like the WASM engine in V8 has its own, separate GC feature, that can also be triggered during Isolate deinitialization (well, the stack trace in the issue basically confirms that).

My attempt to fix that would be basically to skip sending the task after Isolate::Deinit() has been entered. That does fix #31752, and I’m currently compiling V8 to run their test suite and see if that breaks anything. If that works, I’ll try to put together a regression test and open a V8 CL – we’ll see where it goes from there. (It’s generally my experience that proposing concrete changes get things done earlier than opening issues – both in V8 and Node.js 🙂)

but I definitely worry about breaking the contract here.

To be clear, my understanding is that V8 does that, not that we do that.

addaleax · 2020-02-14T16:15:31Z

Landed in e460f8c

This works around a situation in which the V8 WASM code calls into the platform while the Isolate is being disposed. This goes against the V8 API constract for `v8::Platform`. In lieu of a proper fix, it should be okay to keep the Isolate registered; the race condition fixed by 25447d8 cannot occur for the `NodeMainInstance`’s Isolate, as it is the last one to exit in any given Node.js process. This partially reverts 25447d8. Refs: #30909 Refs: #31752 PR-URL: #31795 Reviewed-By: Denys Otrishko <[email protected]> Reviewed-By: James M Snell <[email protected]>

Discard tasks silently that are posted when the Isolate is being disposed. It is not possible to avoid a race condition window between unregistering the Isolate with the platform and disposing it in which background tasks and the Isolate deinit steps themselves may lead to new tasks being posted. The only sensible action in that case is discarding the tasks. Fixes: nodejs#31752 Fixes: https://bugs.chromium.org/p/v8/issues/detail?id=10104 Refs: https://chromium-review.googlesource.com/c/v8/v8/+/2061548 Refs: nodejs#31795 Refs: nodejs#30909

…pose" This reverts commit e460f8c. It is no longer necessary after the previous commit, and restores consistency of the call order between the main thread code, the other call sites, and the documentation. Refs: nodejs#31795

Discard tasks silently that are posted when the Isolate is being disposed. It is not possible to avoid a race condition window between unregistering the Isolate with the platform and disposing it in which background tasks and the Isolate deinit steps themselves may lead to new tasks being posted. The only sensible action in that case is discarding the tasks. Fixes: #31752 Fixes: https://bugs.chromium.org/p/v8/issues/detail?id=10104 Refs: https://chromium-review.googlesource.com/c/v8/v8/+/2061548 Refs: #31795 Refs: #30909 PR-URL: #31853 Reviewed-By: Joyee Cheung <[email protected]>

…pose" This reverts commit e460f8c. It is no longer necessary after the previous commit, and restores consistency of the call order between the main thread code, the other call sites, and the documentation. Refs: #31795 PR-URL: #31853 Reviewed-By: Joyee Cheung <[email protected]>

Discard tasks silently that are posted when the Isolate is being disposed. It is not possible to avoid a race condition window between unregistering the Isolate with the platform and disposing it in which background tasks and the Isolate deinit steps themselves may lead to new tasks being posted. The only sensible action in that case is discarding the tasks. Fixes: #31752 Fixes: https://bugs.chromium.org/p/v8/issues/detail?id=10104 Refs: https://chromium-review.googlesource.com/c/v8/v8/+/2061548 Refs: #31795 Refs: #30909 PR-URL: #31853 Reviewed-By: Joyee Cheung <[email protected]>

…pose" This reverts commit e460f8c. It is no longer necessary after the previous commit, and restores consistency of the call order between the main thread code, the other call sites, and the documentation. Refs: #31795 PR-URL: #31853 Reviewed-By: Joyee Cheung <[email protected]>

Discard tasks silently that are posted when the Isolate is being disposed. It is not possible to avoid a race condition window between unregistering the Isolate with the platform and disposing it in which background tasks and the Isolate deinit steps themselves may lead to new tasks being posted. The only sensible action in that case is discarding the tasks. Fixes: #31752 Fixes: https://bugs.chromium.org/p/v8/issues/detail?id=10104 Refs: https://chromium-review.googlesource.com/c/v8/v8/+/2061548 Refs: #31795 Refs: #30909 PR-URL: #31853 Reviewed-By: Joyee Cheung <[email protected]>

…pose" This reverts commit e460f8c. It is no longer necessary after the previous commit, and restores consistency of the call order between the main thread code, the other call sites, and the documentation. Refs: nodejs#31795 PR-URL: nodejs#31853 Reviewed-By: Joyee Cheung <[email protected]>

…pose" This reverts commit e460f8c. It is no longer necessary after the previous commit, and restores consistency of the call order between the main thread code, the other call sites, and the documentation. Refs: #31795 PR-URL: #31853 Reviewed-By: Joyee Cheung <[email protected]>

nodejs-github-bot added c++ Issues and PRs that require attention from people who are familiar with C++. process Issues and PRs related to the process subsystem. labels Feb 14, 2020

addaleax added fast-track PRs that do not need to wait for 48 hours to land. lib / src Issues and PRs related to general changes in the lib or src directory. and removed process Issues and PRs related to the process subsystem. labels Feb 14, 2020

addaleax mentioned this pull request Feb 14, 2020

v12.16.1 proposal #31781

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lundibundi approved these changes Feb 14, 2020

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jasnell approved these changes Feb 14, 2020

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addaleax closed this Feb 14, 2020

addaleax deleted the node-main-instance-isolate-dispose-order branch February 14, 2020 16:15

codebytere mentioned this pull request Feb 17, 2020

v13.9.0 proposal #31837

Merged

addaleax mentioned this pull request Feb 18, 2020

src: discard tasks posted to platform TaskRunner during shutdown #31853

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addaleax added the v8 platform Issues and PRs related to Node's v8::Platform implementation. label Feb 18, 2020

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src: keep main-thread Isolate attached to platform during Dispose #31795

src: keep main-thread Isolate attached to platform during Dispose #31795

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addaleax commented Feb 14, 2020

src: keep main-thread Isolate attached to platform during Dispose #31795

src: keep main-thread Isolate attached to platform during Dispose #31795

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