repl: Runtime.awaitPromise races with GC when objectGroup is not passed Body #64762

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1. DivyanshuX9 commented on Jul 26, 2026

   

   DivyanshuX9

   on Jul 26, 2026

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   What happened

   The inspector-backed REPL introduced in #64034 evaluates promise-returning expressions using two sequential inspector commands:

   1. Runtime.evaluate (returns a remote promise objectId)
   2. Runtime.awaitPromise (waits for the promise to settle)

   Runtime.evaluate passes objectGroup: this.objectGroup, placing the remote promise object into the REPL's named object group:

   return this.postInterruptible('Runtime.evaluate', {
     ...
     objectGroup: this.objectGroup,
     ...
   }, breakOnSigint);

   However, Runtime.awaitPromise does not pass objectGroup:

   return this.postInterruptible('Runtime.awaitPromise', {
     __proto__: null,
     promiseObjectId: response.result.objectId,
     returnByValue: params.returnByValue,
     generatePreview: params.generatePreview,
   }, breakOnSigint);

   Under GC pressure (observed on the shared-libraries CI configuration), a collection cycle can occur between these two inspector calls. If the remote promise object is collected before Runtime.awaitPromise completes, the inspector returns:

   Inspector error -32000: Promise was collected
   

   Instead of reporting the user's original exception, the REPL surfaces:

   Error [ERR_INSPECTOR_COMMAND]: Inspector error -32000: Promise was collected
   

   This causes test/parallel/test-repl-pretty-stack-custom-writer.mjs to fail.

   ---

   Failing assertion

   Expected:

   Uncaught Error: foo[a]
   

   Actual:

   Uncaught Error [ERR_INSPECTOR_COMMAND]: Inspector error -32000: Promise was collected
   

   ---

   Root cause

   Runtime.awaitPromise accepts an optional objectGroup parameter.

   The promise object is initially associated with the REPL's object group by Runtime.evaluate, but Runtime.awaitPromise does not explicitly pass that group. Under GC pressure, the remote promise object can be collected before the await operation completes, causing the inspector command to fail.

   ---

   Proposed fix

   Pass objectGroup to Runtime.awaitPromise:

   diff --git a/lib/internal/repl/inspector.js b/lib/internal/repl/inspector.js
   @@ -180,9 +180,11 @@ class ReplInspectorChannel {
   -    // Hold the promise open until it resolves or rejects,
   -    // so we can return the final value.
   +    // Hold the promise open until it resolves or rejects.
   +    // Pass objectGroup so the remote promise object remains retained for the
   +    // duration of the await operation.
        return this.postInterruptible('Runtime.awaitPromise', {
          __proto__: null,
          promiseObjectId: response.result.objectId,
          returnByValue: params.returnByValue,
          generatePreview: params.generatePreview,
   +      objectGroup: this.objectGroup,
        }, breakOnSigint);

   Passing the existing object group keeps the remote promise object alive until the await operation completes and prevents the race.

   ---

   Affected file

   • lib/internal/repl/inspector.js

   This code was introduced by #64034 and is not yet present on main.

   ---

   Additional notes

   • This is a follow-up to repl: use inspector over vm #64034 (repl: use inspector over vm).
   • The fix can be applied directly to that PR or submitted as a follow-up after it merges.
   • Updating the test to accept ERR_INSPECTOR_COMMAND would mask the underlying issue instead of fixing it.
   • The issue is reproducible on the shared-libraries CI configuration but is difficult to reproduce consistently on standard builds because it depends on GC timing.
2. Archkon commented on Jul 26, 2026

   

   Archkon

   on Jul 26, 2026 · Hidden as spam

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3. DivyanshuX9 commented on Jul 26, 2026

   

   DivyanshuX9

   on Jul 26, 2026

   Last edited by DivyanshuX9

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   i was not sure about upstreamV8 much since i got this issue in my pr #63651 , so i tried to dig why am i facing the failure, So i have a small fix for that so i just raised the issue
4. DivyanshuX9

   added a commit that references this issue on Jul 26, 2026

   repl: pass objectGroup to Runtime.awaitPromise

   ...

   a16deb3
5. Archkon commented on Jul 26, 2026

   

   Archkon

   on Jul 26, 2026 · Hidden as spam

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6. DivyanshuX9 commented on Jul 26, 2026

   

   DivyanshuX9

   on Jul 26, 2026

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   Thanks for the pointer. I wasn't aware of the upstream V8 issue.

   My understanding was that passing objectGroup to Runtime.awaitPromise keeps the remote promise retained for the duration of the await and avoids the failure on the Node.js side.

   Do you think this workaround is still worth taking in Node, or should we rely entirely on the upstream V8 fix?
7. Archkon commented on Jul 26, 2026

   

   Archkon

   on Jul 26, 2026 · Hidden as spam

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8. DivyanshuX9 commented on Jul 26, 2026

   

   DivyanshuX9

   on Jul 26, 2026

   Last edited by DivyanshuX9

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   I had assumed objectGroup was supported by Runtime.awaitPromise, but i think you're right that it isn't part of the protocol. I'll take another look at the V8 change you linked and understand how ProtocolPromiseHandler::setWeak() is involved before pursuing this further.
9. avivkeller commented on Jul 26, 2026

   

   avivkeller

   on Jul 26, 2026

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   @DivyanshuX9 @Archkon The proposed fix will not work. I'm already coordinating with V8 to fix this. See https://chromium-review.googlesource.com/c/v8/v8/+/8123081
10. avivkeller

    closed this as not plannedon Jul 26, 2026
11. avivkeller

    self-assigned this

    on Jul 26, 2026