[Error] potential listener LEAK — menuService

[vs-code-engineering]

Error Message

unhandlederror-potential listener LEAK detected, popular

Stack Trace

    at a.create (./src/vs/base/common/event.ts:1062:14)
    at nK._event [as onDidChange] (./src/vs/base/common/event.ts:1263:33)
    at Object.u [as onWillAddFirstListener] (./src/vs/platform/actions/common/menuService.ts:437:0)
    at _ke._event [as onDidChange] (./src/vs/base/common/event.ts:1272:19)
    at new mn (./src/vs/platform/actions/browser/toolbar.ts:377:0)
    at a._createInstance (./src/vs/platform/instantiation/common/instantiationService.ts:162:17)
    at a.createInstance (./src/vs/platform/instantiation/common/instantiationService.ts:128:17)
    at $9.renderTemplate (./src/vs/sessions/contrib/changes/browser/changesViewRenderer.ts:205:69)
    at tTt.renderTemplate (./src/vs/base/browser/ui/tree/objectTree.ts:122:29)
    at a.renderTemplate (./src/vs/base/browser/ui/tree/abstractTree.ts:431:0)
    at (anonymous) (./src/vs/base/browser/ui/list/listWidget.ts:1273:35)
    at vci.renderTemplate (./src/vs/base/browser/ui/list/listWidget.ts:1273:24)
    at Mxt.alloc (./src/vs/base/browser/ui/list/rowCache.ts:40:33)
    at GR.insertItemInDOM (./src/vs/base/browser/ui/list/listView.ts:962:30)
    at (anonymous) (./src/vs/base/browser/ui/list/listView.ts:931:10)
    at makeChanges (./src/vs/base/browser/ui/list/rowCache.ts:69:3)
    at GR.render (./src/vs/base/browser/ui/list/listView.ts:922:13)
    at GR.onScroll (./src/vs/base/browser/ui/list/listView.ts:1165:8)
    at E._deliver (./src/vs/base/common/event.ts:1355:12)
    at E._deliverQueue (./src/vs/base/common/event.ts:1366:8)

Raw Stack Trace (minified)

Error     at a.create (out/vs/sessions/sessions.desktop.main.js:403:18384)     at nK._event [as onDidChange] (out/vs/sessions/sessions.desktop.main.js:405:1891)     at Object.u [as onWillAddFirstListener] (out/vs/sessions/sessions.desktop.main.js:852:136321)     at _ke._event [as onDidChange] (out/vs/sessions/sessions.desktop.main.js:405:2158)     at new mn (out/vs/sessions/sessions.desktop.main.js:852:141166)     at a._createInstance (out/vs/sessions/sessions.desktop.main.js:1466:2000)     at a.createInstance (out/vs/sessions/sessions.desktop.main.js:1466:1440)     at $9.renderTemplate (out/vs/sessions/sessions.desktop.main.js:4115:12219)     at tTt.renderTemplate (out/vs/sessions/sessions.desktop.main.js:861:18655)     at a.renderTemplate (out/vs/sessions/sessions.desktop.main.js:860:17232)     at out/vs/sessions/sessions.desktop.main.js:728:2084     at Array.map (<anonymous>)     at vci.renderTemplate (out/vs/sessions/sessions.desktop.main.js:728:2075)     at Mxt.alloc (out/vs/sessions/sessions.desktop.main.js:685:5675)     at GR.insertItemInDOM (out/vs/sessions/sessions.desktop.main.js:685:21720)     at out/vs/sessions/sessions.desktop.main.js:685:21230     at Mxt.transact (out/vs/sessions/sessions.desktop.main.js:685:5912)     at GR.render (out/vs/sessions/sessions.desktop.main.js:685:21090)     at GR.onScroll (out/vs/sessions/sessions.desktop.main.js:685:27657)     at E._deliver (out/vs/sessions/sessions.desktop.main.js:405:3150)     at E._deliverQueue (out/vs/sessions/sessions.desktop.main.js:405:3239)     at E.fire (out/vs/sessions/sessions.desktop.main.js:405:3574)     at _ye.value (out/vs/sessions/sessions.desktop.main.js:483:36808)     at E._deliver (out/vs/sessions/sessions.desktop.main.js:405:3150)     at E.fire (out/vs/sessions/sessions.desktop.main.js:405:3469)     at $_._setState (out/vs/sessions/sessions.desktop.main.js:414:21424)     at $_.setScrollDimensions (out/vs/sessions/sessions.desktop.main.js:414:19430)     at oF.setScrollDimensions (out/vs/sessions/sessions.desktop.main.js:483:39181)     at GR.layout (out/vs/sessions/sessions.desktop.main.js:685:20360)     at uui.layout (out/vs/sessions/sessions.desktop.main.js:728:10167)     at iM.layout (out/vs/sessions/sessions.desktop.main.js:860:56372)     at _ye.value (out/vs/sessions/sessions.desktop.main.js:4121:28357)     at E._deliver (out/vs/sessions/sessions.desktop.main.js:405:3150)     at E.fire (out/vs/sessions/sessions.desktop.main.js:405:3469)     at Object.layout (out/vs/sessions/sessions.desktop.main.js:1299:113533)     at co (out/vs/sessions/sessions.desktop.main.js:1299:112038)     at Object.G [as runAndSubscribe] (out/vs/sessions/sessions.desktop.main.js:403:15951)     at XMe.create (out/vs/sessions/sessions.desktop.main.js:1299:112073)     at jM.createModalEditorPart (out/vs/sessions/sessions.desktop.main.js:1299:122423)     at otn (out/vs/sessions/sessions.desktop.main.js:1299:56827)     at whe (out/vs/sessions/sessions.desktop.main.js:1299:55243)     at a.invokeFunction (out/vs/sessions/sessions.desktop.main.js:1466:944)     at bN.resolveUntypedInputAndGroup (out/vs/sessions/sessions.desktop.main.js:1347:51939)     at bN.resolveEditor (out/vs/sessions/sessions.desktop.main.js:1347:52185)     at Rhe.openEditor (out/vs/sessions/sessions.desktop.main.js:1347:44707)     at bqe._openFileItem (out/vs/sessions/sessions.desktop.main.js:4121:30313)     at _ye.value (out/vs/sessions/sessions.desktop.main.js:4121:23696)     at E._deliver (out/vs/sessions/sessions.desktop.main.js:405:3150)     at E.fire (out/vs/sessions/sessions.desktop.main.js:405:3469)     at Mui._open (out/vs/sessions/sessions.desktop.main.js:861:61260)     at Mui.onPointer (out/vs/sessions/sessions.desktop.main.js:861:60943)     at _ye.value (out/vs/sessions/sessions.desktop.main.js:861:60075)     at E._deliver (out/vs/sessions/sessions.desktop.main.js:405:3150)     at E.fire (out/vs/sessions/sessions.desktop.main.js:405:3469)     at _ye.value (out/vs/sessions/sessions.desktop.main.js:403:11566)     at E._deliver (out/vs/sessions/sessions.desktop.main.js:405:3150)     at E.fire (out/vs/sessions/sessions.desktop.main.js:405:3469)     at dui.onViewPointer (out/vs/sessions/sessions.desktop.main.js:685:48200)     at dui.onViewPointer (out/vs/sessions/sessions.desktop.main.js:860:47487)     at _ye.value (out/vs/sessions/sessions.desktop.main.js:403:11923)     at E._deliver (out/vs/sessions/sessions.desktop.main.js:405:3150)     at E.fire (out/vs/sessions/sessions.desktop.main.js:405:3469)     at _ye.value (out/vs/sessions/sessions.desktop.main.js:403:11566)     at E._deliver (out/vs/sessions/sessions.desktop.main.js:405:3150)     at E.fire (out/vs/sessions/sessions.desktop.main.js:405:3469)     at HTMLDivElement.o (out/vs/sessions/sessions.desktop.main.js:483:63361)

Details

Property	Value
Bucket ID	66c2ab70-9fd3-b4ab-43f7-4f41cdfa38b7
Version	1.117.0-insider
Commit	98b4d3e2
Last Seen	Wed Apr 15 2026 18:04:58 GMT+0000 (Coordinated Universal Time)
Platforms	Mac, Windows, Linux
Product	Agents

---

This issue was automatically created from the VS Code Errors Dashboard

[vs-code-engineering]

🔍 Error Investigation

Summary

The PersistedMenuHideState._onDidChange emitter (a singleton shared by all MenuImpl instances) is accumulating too many listeners. In the Agents workbench, the global leak warning threshold is set to 175. The ChangesTreeRenderer.renderTemplate() in changesViewRenderer.ts creates a new MenuWorkbenchToolBar for every tree-row template, and each toolbar's internal MenuImpl subscribes to this shared emitter. When a session has enough file changes to fill the viewport (creating ~30–50 templates), the total subscriber count — combined with all other menus in the app — exceeds 175, triggering the "popular" leak warning. The error fires on scroll/layout when new tree rows are rendered.

Culprit Commit

No single recent commit introduced this regression. The per-template toolbar pattern has been present since changesViewRenderer.ts was extracted from changesView.ts in PR #307903 (April 5). The error first surfaced on commit 98b4d3e2 (April 14) because that was the first Insiders build where enough Agents users had sessions with large enough working sets to cross the 175-listener threshold. The recent-regression label reflects that the error bucket is new to this build, not that the underlying code pattern changed.

Code Flow

sequenceDiagram
    participant User as User (click/scroll)
    participant ListView as ListView.render()
    participant RowCache as RowCache.alloc()
    participant Renderer as ChangesTreeRenderer.renderTemplate()
    participant Toolbar as MenuWorkbenchToolBar
    participant MenuImpl as MenuImpl (onDidChange)
    participant HiddenState as PersistedMenuHideState._onDidChange

    User->>ListView: scroll / layout
    ListView->>RowCache: alloc template
    RowCache->>Renderer: renderTemplate()
    Note over Renderer: ⚠️ Root cause:<br/>Creates new MenuWorkbenchToolBar<br/>per template (line 205)
    Renderer->>Toolbar: new MenuWorkbenchToolBar(MenuId.ChatEditingSessionChangeToolbar)
    Toolbar->>MenuImpl: subscribe to menu.onDidChange
    MenuImpl->>HiddenState: subscribe to hiddenStates.onDidChange (line 437)
    Note over HiddenState: 💥 LeakageMonitor.check()<br/>listenerCount ≥ 175 threshold<br/>→ ListenerLeakError("popular")

Loading

Affected Files

File	Role
src/vs/sessions/contrib/changes/browser/changesViewRenderer.ts:205	Root cause — creates per-template MenuWorkbenchToolBar
src/vs/platform/actions/common/menuService.ts:437	startLazyListener() subscribes each MenuImpl to shared hiddenStates.onDidChange
src/vs/platform/actions/common/menuService.ts:59	PersistedMenuHideState._onDidChange — the leaking emitter (singleton)
src/vs/base/common/event.ts:1008-1034	LeakageMonitor.check() — detects the leak
src/vs/sessions/browser/workbench.ts:345	Sets global leak threshold to 175

Repro Steps

1. Launch VS Code Agents (Insiders 1.117.0+)
2. Start or open an agent session that has many file changes (30+ modified files)
3. Open the Changes view in the sidebar so the file tree is visible
4. Scroll through the changes list or resize the window to trigger new row rendering
5. The error fires when enough tree-row templates accumulate, each subscribing their toolbar's menu to PersistedMenuHideState._onDidChange

The likelihood increases with more files in the session and a larger viewport (more visible rows = more templates).

Fix Proposal

Fix location: src/vs/sessions/contrib/changes/browser/changesViewRenderer.ts → renderTemplate()

Approach: Instead of creating a new MenuWorkbenchToolBar (and thus a new MenuImpl subscriber to hiddenStates.onDidChange) in every renderTemplate() call, defer toolbar creation to renderElement() and dispose it in disposeElement(). This way, only the currently-visible rows have active toolbar/menu subscriptions, and the subscriber count stays proportional to the viewport rather than accumulating over the tree's lifetime.

Alternatively, the PersistedMenuHideState._onDidChange emitter could be created with an explicit higher leakWarningThreshold (e.g., new Emitter<void>({ leakWarningThreshold: 500 })) since it is architecturally expected to have many subscribers across all menus in the application. However, this would mask the symptom rather than fix the underlying per-template allocation pattern.

Recommended Owner

@lszomoru — primary developer of the sessions/changes area; authored the changesViewRenderer.ts extraction (PR #307903) and multiple sessions toolbar/context-key PRs.

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