[Unhandled Error] potential listener LEAK detected, popular — search/searchResultsView / toolbar → menuService #308255

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1. vs-code-engineering

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   bugIssue identified by VS Code Team member as probable bugIssue identified by VS Code Team member as probable bug

   error-telemetryVS Code - Issues generated by telemetryVS Code - Issues generated by telemetry

   recent-regression

   on Apr 7, 2026
2. vs-code-engineering

   assigned

   Bryan Chen (bryanchen-d)

   on Apr 7, 2026
3. vs-code-engineering commented on Apr 7, 2026

   

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4. vs-code-engineering commented on Apr 7, 2026

   

   vs-code-engineeringBot

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   🔍 Error Investigation

   Summary

   The error potential listener LEAK detected, popular fires on the singleton PersistedMenuHideState._onDidChange emitter in menuService.ts. Every MenuImpl that has an active onDidChange listener subscribes to this shared emitter. The search results view creates a MenuWorkbenchToolBar (and thus a MenuImpl) for each template across 4 renderers (TextSearchResultRenderer, FolderMatchRenderer, FileMatchRenderer, MatchRenderer), pushing the total listener count above the global leak threshold of 175. Affects 119+ users across all platforms.

   Culprit Commit

   No single commit in the range 54b695e0...b826afb9 directly modifies the affected files (event.ts, menuService.ts, toolbar.ts, searchResultsView.ts). This regression is a threshold-crossing event: the total number of active MenuImpl instances across the entire application grew past the 175 global leak warning threshold. The 29 commits in the range include multiple Sessions/Agents UI additions that cumulatively add new menus and toolbars to the app, each subscribing to the shared PersistedMenuHideState._onDidChange emitter. The search results view is the "straw that broke the camel's back" — it creates many templates rapidly when rendering results, triggering the leak detection.

   Code Flow

   sequenceDiagram
       participant Search as SearchResultsView<br/>renderTemplate()
       participant Toolbar as MenuWorkbenchToolBar<br/>constructor
       participant MenuImpl as MenuImpl<br/>constructor
       participant HiddenStates as PersistedMenuHideState<br/>._onDidChange (singleton)
       participant LeakMon as LeakageMonitor
   
       Search->>Toolbar: createInstance(MenuWorkbenchToolBar, MenuId.SearchActionMenu)
       Toolbar->>MenuImpl: menuService.createMenu(menuId)
       Toolbar->>MenuImpl: menu.onDidChange(callback)
       Note over MenuImpl: First listener → onWillAddFirstListener
       MenuImpl->>HiddenStates: hiddenStates.onDidChange(callback)
       Note over HiddenStates: ⚠️ Root cause:<br/>Singleton emitter with default<br/>threshold (175), receives one<br/>listener per active MenuImpl
       HiddenStates->>LeakMon: check(stack, listenerCount)
       Note over LeakMon: 💥 listenerCount ≥ 175<br/>Error: "potential listener<br/>LEAK detected, popular"
   

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   Affected Files

   File	Role
   src/vs/platform/actions/common/menuService.ts:59-60	Root cause — PersistedMenuHideState._onDidChange singleton Emitter with no custom leak threshold
   src/vs/platform/actions/common/menuService.ts:437	Each MenuImpl.startLazyListener() subscribes to hiddenStates.onDidChange
   src/vs/platform/actions/browser/toolbar.ts:377	MenuWorkbenchToolBar constructor subscribes to _menu.onDidChange, triggering lazy listener
   src/vs/workbench/contrib/search/browser/searchResultsView.ts:123,227,328,422	4 renderers each create MenuWorkbenchToolBar per template — leak trigger
   src/vs/base/common/event.ts:1008-1034	LeakageMonitor.check() — fires the leak error when listenerCount ≥ threshold
   src/vs/workbench/browser/workbench.ts:135	Sets _globalLeakWarningThreshold to 175

   Repro Steps

   1. Open VS Code Insiders (1.115.0+, commit b826afb9 or later)
   2. Open a workspace with many files (e.g., the VS Code repo itself)
   3. Open the Search view (Ctrl+Shift+F / Cmd+Shift+F)
   4. Perform a search that returns many results (e.g., search for import)
   5. Expand several file matches so many match rows are visible
   6. The leak error fires in telemetry when the total count of MenuImpl instances subscribing to hiddenStates.onDidChange exceeds 175

   The error is more likely to trigger when VS Code has many menus active (editor tabs, sidebar panels, toolbars) in addition to the search results.

   Fix Proposal

   Option A (quick fix) — Increase the leak threshold on the singleton emitter:

   Fix location: src/vs/platform/actions/common/menuService.ts → PersistedMenuHideState class
   Approach: Change line 59 from new Emitter(void)() to new Emitter(void)({ leakWarningThreshold: 500 }). This emitter is a singleton that legitimately receives one listener per active MenuImpl in the entire application, so 175 is too low.

   Option B (structural fix) — Decouple search result templates from per-instance menus:

   Fix location: src/vs/workbench/contrib/search/browser/searchResultsView.ts → all 4 renderTemplate() methods
   Approach: Instead of creating a MenuWorkbenchToolBar (and thus a MenuImpl) per template, share a single menu instance per renderer type. The toolbar can refresh its context on renderElement without needing a dedicated MenuImpl per row. This reduces the listener count on hiddenStates.onDidChange by ~100+.

   Option C (hybrid) — Apply both fixes: raise the threshold to avoid false positives, and refactor search templates for efficiency.

   Recommended Owner

   @bryanchen-d is already assigned (error-telemetry area owner). For the fix itself, @osortega (Search area owner per working-areas.md) is the recommended owner, as the primary fix involves the search results view template pattern. For Option A (menuService threshold), @jrieken (platform/performance owner) may want to weigh in on the appropriate threshold value.

   Generated by errors-investigate · ◷
5. bryanchen-d commented on Apr 7, 2026

   

   Bryan Chen (bryanchen-d)

   on Apr 7, 2026

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   as per analysis, this is more a false alarm:

   The global leak threshold is set to 175 in workbench.ts:135. It just wasn't tuned for a scenario where 4 renderer types each create toolbars across hundreds of search result rows. This is a false positive from too many legitimate subscribers, not an actual leak.
6. vs-code-engineering commented on Apr 8, 2026

   

   vs-code-engineeringBot

   on Apr 8, 2026 – with VS Code Engineering

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   Related Error Buckets

   These additional error buckets are tracked by this issue (v1.114.0):

   Bucket ID	Error Message	Version
   18361d63	potential listener LEAK detected, popular	1.114.0

   Stack path: event.ts → menuService.ts:437 → toolbar.ts:377 → instantiationService → searchResultsView.ts:422 — same search results view toolbar listener leak pattern as the primary bucket (different line in searchResultsView.ts but same code path through toolbar initialization).

   Generated by errors-triage · ◷
7. Bryan Chen (bryanchen-d)

   changed the title [-][Unhandled Error] potential listener LEAK detected, popular[/-] [+][Unhandled Error] potential listener LEAK detected, popular — search/searchResultsView / toolbar → menuService[/+] on Apr 14, 2026
8. vs-code-engineering commented on Apr 17, 2026

   

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9. vs-code-engineering commented on Apr 21, 2026

   

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   Related Error Buckets

   These error buckets continue to appear in v1.117.0-insider (previously tracked since v1.115.0-insider):

   Bucket ID	Error Message	Users	Path
   5912c915	potential listener LEAK detected, popular	207	searchResultsView.ts:422 → menuService.ts:437 → toolbar.ts:377
   ccfc3902	potential listener LEAK detected, popular	122	searchResultsView.ts:328 → menuService.ts:437 → toolbar.ts:377
   aa1cb938	potential listener LEAK detected, popular	32	searchResultsView.ts:422 → toolbar.ts:382

   These additional error buckets are tracked by this issue (v1.117.0-insider):

   Bucket ID	Error Message	Users	Path
   634c9a3e	potential listener LEAK detected, popular	35	toolbar.ts:382 → codeBlockPart.ts:210 → chatMarkdownContentPart.ts:438 (chat code block)

   All from commit [173f07e5]((insiders.vscode.dev/redacted) (Apr 20 build). The first three are the same search results view / menuService / toolbar pattern. The 634c9a3e bucket is a new triggering path: the toolbar listener leak fired from chat code block rendering instead of search results.

   Generated by errors-regression-scan · ● 15.8M · ◷
10. vs-code-engineering commented on Apr 22, 2026

    

    vs-code-engineeringBot

    on Apr 22, 2026 – with VS Code Engineering

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    Related Error Buckets

    These additional error buckets are tracked by this issue (v1.116.0):

    Bucket ID	Error Message	Version
    a0686ebe	potential listener LEAK detected, popular	1.116.0

    Stack path: event.ts → menuService.ts:437 → toolbar.ts → searchResultsView.ts (renderTemplate) — same search results view / menuService / toolbar listener leak pattern as the primary bucket (new bucket ID from minification drift on v1.116.0 stable). 89.6K users, 1.2M hits.

    Generated by errors-triage · ● 3.7M · ◷
11. Bryan Chen (bryanchen-d)

    added

    ai-generatedGenerated by AI automation workflowsGenerated by AI automation workflows

    ai-analyzedAI automation workflow has run an analysis of this issue and provided a comment.AI automation workflow has run an analysis of this issue and provided a comment.

    on Apr 28, 2026
12. vs-code-engineering commented on Aug 11, 2026

    

    vs-code-engineeringBot

    on Aug 11, 2026 – with VS Code Engineering

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    Related Error Buckets

    These error buckets continue to appear in v1.132.0 (previously tracked since v1.114.0):

    Bucket	Error Message	Version
    18361d63	unhandlederror-potential listener LEAK detected, popular	1.132.0

    This is a continuation of the previously-tracked listener leak, not a new regression.

    Generated by errors-triage · opus48 · 110.7 AIC · ⌖ 10.1 AIC · ⊞ 10.5K · ◷