fix(query-core): Keep observer notifications stable by scttcper · Pull Request #11234 · TanStack/query

scttcper · 2026-08-20T00:36:53Z

PR #11214 changed observer removal from filter() to splice(). That made removing lots of observers much faster, but it also allowed an observer to change the same array while a query was notifying it. If an observer unsubscribed synchronously, the next observer could be skipped and left with stale data.

This notifies a shallow copy of the observer array. The removal path still uses splice(), so the performance improvement from #11214 stays.

I ran a local Vitest benchmark that calls setQueryData on one query with all observers subscribed:

Observers	Before	After
10	0.0027 ms	0.0027 ms
50	0.0096 ms	0.0101 ms
10,000	2.6049 ms	2.6032 ms

There isn't a meaningful change in notification time. The key change and unmount paths measured in #11214 are unchanged because this does not change observer removal.

Summary by CodeRabbit

Bug Fixes
- Fixed query updates so all remaining observers are notified correctly when another observer unsubscribes during notification.
- Ensured observers receive the latest query data consistently during synchronous updates.
Tests
- Added regression coverage for observer notifications during unsubscribe scenarios.
Release
- Included in a patch release of @tanstack/query-core.

Removing an observer in place can shift the active notification loop and skip the next observer. Iterate over a shallow copy so synchronous unsubscriptions keep the old behavior without giving up the faster removal path from TanStack#11214. Co-Authored-By: Codex <noreply@openai.com>

coderabbitai · 2026-08-20T00:37:03Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: b133350a-a59a-4e5c-a4be-d39fc870d97e

📥 Commits

Reviewing files that changed from the base of the PR and between 64a8035 and 131504a.

📒 Files selected for processing (3)

.changeset/stable-observers-notify.md
packages/query-core/src/__tests__/query.test.tsx
packages/query-core/src/query.ts

Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review.

📝 Walkthrough

Walkthrough

The query dispatch path now snapshots observers before notification. A regression test verifies that remaining observers receive updated data after one observer unsubscribes synchronously. A patch changeset documents the fix.

Changes

Observer notification stability

Layer / File(s)	Summary
Stable dispatch and regression coverage `packages/query-core/src/query.ts`, `packages/query-core/src/__tests__/query.test.tsx`, `.changeset/stable-observers-notify.md`	`Query.#dispatch` iterates over a snapshot of observers. The regression test verifies notification of the remaining observer after synchronous unsubscription. The changeset declares a patch release.
Estimated code review effort: 2 (Simple)	~10 minutes

Merge Risk:⚪ Minimal · up to 13150

This localized change stabilizes observer notifications while preserving the existing removal performance improvement, and no actionable merge-blocking risk remains after normal checks and review.

Possibly related PRs

TanStack/query#11231: This PR applies the same observer snapshot fix and regression coverage.
TanStack/query#11214: Both PRs change observer-array handling in packages/query-core/src/query.ts.

Suggested reviewers:tkdodo

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main change: stabilizing query observer notifications during synchronous unsubscription.
Description check	✅ Passed	The description explains the bug, fix, performance impact, and benchmark results, but it omits the template checklist and release-impact headings.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

Create PR with unit tests

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

_{Comment @coderabbitai help to get the list of available commands.}

nx-cloud · 2026-08-20T07:59:02Z

View your CI Pipeline Execution ↗ for commit 131504a

Command	Status	Duration	Result
`nx affected --targets=test:sherif,test:knip,tes...`	✅ Succeeded	7m 45s	View ↗
`nx run-many --target=build --exclude=examples/*...`	✅ Succeeded	44s	View ↗

☁️ Nx Cloud last updated this comment at 2026-08-20 08:07:42 UTC

pkg-pr-new · 2026-08-20T08:01:06Z

More templates

@tanstack/angular-query-experimental

npm i https://pkg.pr.new/@tanstack/angular-query-experimental@11234

@tanstack/eslint-plugin-query

npm i https://pkg.pr.new/@tanstack/eslint-plugin-query@11234

@tanstack/lit-query

npm i https://pkg.pr.new/@tanstack/lit-query@11234

@tanstack/preact-query

npm i https://pkg.pr.new/@tanstack/preact-query@11234

@tanstack/preact-query-devtools

npm i https://pkg.pr.new/@tanstack/preact-query-devtools@11234

@tanstack/preact-query-persist-client

npm i https://pkg.pr.new/@tanstack/preact-query-persist-client@11234

@tanstack/query-async-storage-persister

npm i https://pkg.pr.new/@tanstack/query-async-storage-persister@11234

@tanstack/query-broadcast-client-experimental

npm i https://pkg.pr.new/@tanstack/query-broadcast-client-experimental@11234

@tanstack/query-core

npm i https://pkg.pr.new/@tanstack/query-core@11234

@tanstack/query-devtools

npm i https://pkg.pr.new/@tanstack/query-devtools@11234

@tanstack/query-persist-client-core

npm i https://pkg.pr.new/@tanstack/query-persist-client-core@11234

@tanstack/query-sync-storage-persister

npm i https://pkg.pr.new/@tanstack/query-sync-storage-persister@11234

@tanstack/react-query

npm i https://pkg.pr.new/@tanstack/react-query@11234

@tanstack/react-query-devtools

npm i https://pkg.pr.new/@tanstack/react-query-devtools@11234

@tanstack/react-query-next-experimental

npm i https://pkg.pr.new/@tanstack/react-query-next-experimental@11234

@tanstack/react-query-persist-client

npm i https://pkg.pr.new/@tanstack/react-query-persist-client@11234

@tanstack/solid-query

npm i https://pkg.pr.new/@tanstack/solid-query@11234

@tanstack/solid-query-devtools

npm i https://pkg.pr.new/@tanstack/solid-query-devtools@11234

@tanstack/solid-query-persist-client

npm i https://pkg.pr.new/@tanstack/solid-query-persist-client@11234

@tanstack/svelte-query

npm i https://pkg.pr.new/@tanstack/svelte-query@11234

@tanstack/svelte-query-devtools

npm i https://pkg.pr.new/@tanstack/svelte-query-devtools@11234

@tanstack/svelte-query-persist-client

npm i https://pkg.pr.new/@tanstack/svelte-query-persist-client@11234

@tanstack/vue-query

npm i https://pkg.pr.new/@tanstack/vue-query@11234

@tanstack/vue-query-devtools

npm i https://pkg.pr.new/@tanstack/vue-query-devtools@11234

commit: 131504a

scttcper marked this pull request as ready for review August 20, 2026 00:38

TkDodo mentioned this pull request Aug 20, 2026
fix(query-core): notify sibling observers when one unsubscribes during dispatch #11231
Closed

TkDodo approved these changes Aug 20, 2026
View reviewed changes

TkDodo merged commit 9656dc4 into TanStack:mainAug 20, 2026
9 checks passed

github-actionsBot mentioned this pull request Aug 20, 2026
ci: Version Packages #11206
Open

Navigation Menu

Uh oh!

Uh oh!

fix(query-core): Keep observer notifications stable - #11234

fix(query-core): Keep observer notifications stable#11234
TkDodo merged 1 commit into
TanStack:mainfrom
scttcper:scttcper/observer-notification-test

scttcper commented Aug 20, 2026•
edited by coderabbitai Bot
Loading

Uh oh!

coderabbitaiBot commented Aug 20, 2026•
edited
Loading

Walkthrough

Changes

Uh oh!

nx-cloudBot commented Aug 20, 2026•
edited
Loading

Uh oh!

pkg-pr-newBot commented Aug 20, 2026

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Uh oh!

Uh oh!

Conversation

scttcper commented Aug 20, 2026• edited by coderabbitai BotLoading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Summary by CodeRabbit

Uh oh!

coderabbitaiBot commented Aug 20, 2026• edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Walkthrough

Changes

Uh oh!

nx-cloudBot commented Aug 20, 2026• edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

pkg-pr-newBot commented Aug 20, 2026

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

scttcper commented Aug 20, 2026•
edited by coderabbitai Bot
Loading

coderabbitaiBot commented Aug 20, 2026•
edited
Loading

nx-cloudBot commented Aug 20, 2026•
edited
Loading