[Error] unhandlederror-[ThemeService.onColorThemeChange] potential listener LEAK detected, popular — documentSemanticTokens

[vs-code-engineering]

Error Message

unhandlederror-[ThemeService.onColorThemeChange] potential listener LEAK detected, popular

Stack Trace

    at a.create (./src/vs/base/common/event.ts:1068:14)
    at Gee._event (./src/vs/base/common/event.ts:1272:33)
    at new MF (./src/vs/editor/contrib/semanticTokens/browser/documentSemanticTokens.ts:178:30)
    at c (./src/vs/editor/contrib/semanticTokens/browser/documentSemanticTokens.ts:46:33)
    at register (./src/vs/editor/contrib/semanticTokens/browser/documentSemanticTokens.ts:87:4)
    at T._deliver (./src/vs/base/common/event.ts:1364:12)
    at T._deliverQueue (./src/vs/base/common/event.ts:1375:8)
    at T.fire (./src/vs/base/common/event.ts:1399:8)
    at yet.createModel (./src/vs/editor/common/services/modelService.ts:449:21)
    at G0.doCreateTextEditorModel (./src/vs/workbench/common/editor/textEditorModel.ts:172:0)
    at G0.createTextEditorModel (./src/vs/workbench/common/editor/textEditorModel.ts:166:0)
    at G0.doCreateTextModel (./src/vs/workbench/services/textfile/common/textFileEditorModel.ts:565:0)
    at G0.resolveFromContent (./src/vs/workbench/services/textfile/common/textFileEditorModel.ts:547:0)
    at G0.resolveFromFile (./src/vs/workbench/services/textfile/common/textFileEditorModel.ts:471:0)
    at async G0.resolve (./src/vs/workbench/services/textfile/common/textFileEditorModel.ts:307:0)
    at async PGe.doResolve (./src/vs/workbench/services/textfile/common/textFileEditorModelManager.ts:446:0)
    at async get.doCreateReferencedObject (./src/vs/workbench/services/textmodelResolver/common/textModelResolverService.ts:57:17)
    at async sIe.acquire (./src/vs/base/common/lifecycle.ts:727:18)
    at async fet.createModelReference (./src/vs/workbench/services/textmodelResolver/common/textModelResolverService.ts:242:9)
    at async ZTe._handleAsResourceInput (./src/vs/workbench/api/browser/mainThreadDocuments.ts:286:14)

Raw Stack Trace (minified)

Error     at a.create (out/vs/workbench/workbench.desktop.main.js:403:18436)     at Gee._event (out/vs/workbench/workbench.desktop.main.js:405:2009)     at new MF (out/vs/workbench/workbench.desktop.main.js:923:48048)     at c (out/vs/workbench/workbench.desktop.main.js:923:45618)     at fIe.value (out/vs/workbench/workbench.desktop.main.js:923:46109)     at T._deliver (out/vs/workbench/workbench.desktop.main.js:405:3268)     at T._deliverQueue (out/vs/workbench/workbench.desktop.main.js:405:3357)     at T.fire (out/vs/workbench/workbench.desktop.main.js:405:3692)     at yet.createModel (out/vs/workbench/workbench.desktop.main.js:1810:977)     at G0.doCreateTextEditorModel (out/vs/workbench/workbench.desktop.main.js:936:15249)     at G0.createTextEditorModel (out/vs/workbench/workbench.desktop.main.js:936:15075)     at G0.doCreateTextModel (out/vs/workbench/workbench.desktop.main.js:1785:17780)     at G0.resolveFromContent (out/vs/workbench/workbench.desktop.main.js:1785:17617)     at G0.resolveFromFile (out/vs/workbench/workbench.desktop.main.js:1785:16719)     at async G0.resolve (out/vs/workbench/workbench.desktop.main.js:1785:14593)     at async PGe.doResolve (out/vs/workbench/workbench.desktop.main.js:4910:8863)     at async get.doCreateReferencedObject (out/vs/workbench/workbench.desktop.main.js:1785:27870)     at async sIe.acquire (out/vs/workbench/workbench.desktop.main.js:403:3866)     at async fet.createModelReference (out/vs/workbench/workbench.desktop.main.js:1785:30166)     at async ZTe._handleAsResourceInput (out/vs/workbench/workbench.desktop.main.js:969:11608)     at async ZTe.$tryOpenDocument (out/vs/workbench/workbench.desktop.main.js:969:10864)

Details

Property	Value
Bucket ID	65a895ff-3805-0ec6-03e9-1361e485f06b
Version	1.118.0-insider
Commit	659d444a
Last Seen	Thu Apr 23 2026 23:58:27 GMT+0000 (Coordinated Universal Time)
Platforms	Mac, Windows, Linux
Product	VSCode

---

This issue was automatically created from the VS Code Errors Dashboard

[vs-code-engineering]

Regression Details

• Product: VSCode
• Regression type: new
• Last release without this error: 1.117.0-insider (7f0183b, Apr 21)
• First release with this error: 1.118.0-insider (102df5b, Apr 22)
• Commit range: 7f0183b5...102df5b5
• Users on target build: 59

Deminified Stack Summary

The emitter is ThemeService.onColorThemeChange. The leak occurs at documentSemanticTokens.ts:178 where semantic tokens subscribe to a color theme change event. The call path:

1. event.ts → leak monitoring fires
2. documentSemanticTokens.ts:178 → constructor subscribes to theme change
3. documentSemanticTokens.ts:46/87 → registration flow
4. Triggered by modelService.ts:449 → createModel → textEditorModel.ts → textFileEditorModel.ts → file resolve

This is a popular leak — the ThemeService.onColorThemeChange emitter has too many subscribers from DocumentSemanticTokens instances that aren't properly cleaned up.

Related Issues

• [Error] potential listener LEAK — documentSemanticTokens #311542 — Same component (documentSemanticTokens.ts:178) but for Agents product, triggered via multiDiffEditorViewModel

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[vs-code-engineering]

🔍 Error Investigation

Summary

This error bucket was created by a telemetry grouping change, not a new listener leak. PR #311728 added leakWarningName: 'ThemeService.onColorThemeChange' to the theme service emitter, which changed the error message from the generic potential listener LEAK detected, popular to [ThemeService.onColorThemeChange] potential listener LEAK detected, popular, producing a new telemetry bucket. The underlying listener accumulation on ThemeService.onColorThemeChange (threshold: 400) is pre-existing — each open text model registers a listener via ModelSemanticColoring, and with many other theme-change subscribers, the threshold is exceeded for users with many open files.

Culprit Commit

Field	Value
Commit	4dabc9bb
Author	@bryanchen-d
PR	#311728
Message	feat: add leakWarningName to emitters for better leak error telemetry grouping
Why	Added leakWarningName: 'ThemeService.onColorThemeChange' to the emitter in workbenchThemeService.ts, changing the error message format and creating a new telemetry bucket for a pre-existing listener accumulation.

Code Flow

sequenceDiagram
    participant Main as mainThreadDocuments
    participant TF as textFileEditorModel
    participant MS as modelService
    participant DST as DocumentSemanticTokensFeature
    participant MSC as ModelSemanticColoring
    participant TS as ThemeService.onColorThemeChange

    Main->>TF: resolve() → createModel
    TF->>MS: createModel()
    MS->>DST: onModelAdded fires
    DST->>MSC: new ModelSemanticColoring(model)
    Note over MSC: Constructor at line 178
    MSC->>TS: themeService.onDidColorThemeChange(...)
    Note over TS: ⚠️ Listener count exceeds<br/>threshold (400).<br/>Each model adds one listener.
    Note over TS: 💥 ListenerLeakError thrown:<br/>[ThemeService.onColorThemeChange]<br/>potential listener LEAK detected, popular

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Affected Files

File	Role
src/vs/workbench/services/themes/browser/workbenchThemeService.ts	Emitter definition with threshold=400 and new leakWarningName (root cause of new bucket)
src/vs/editor/contrib/semanticTokens/browser/documentSemanticTokens.ts	Each ModelSemanticColoring subscribes to theme change (line 178) — primary listener source
src/vs/base/common/event.ts	Leak detection infrastructure — ListenerLeakError now includes emitter name

Repro Steps

1. Open VS Code Insiders (1.118.0+, commit 659d444a or later)
2. Open a workspace with many files (200+ text models, or have extensions that open many virtual documents)
3. The ThemeService.onColorThemeChange emitter accumulates listeners: one per ModelSemanticColoring instance plus many other theme-change subscribers across the codebase
4. When total listener count exceeds 400, the leak warning fires
5. The "popular" classification means no single subscriber source dominates (≤30% of total), confirming multiple different code paths subscribe

Fix Proposal

Two options depending on whether the threshold is appropriate:

Option A — Increase the threshold (if 400+ listeners is expected for power users):
Fix location: src/vs/workbench/services/themes/browser/workbenchThemeService.ts → onColorThemeChange emitter
Approach: Increase leakWarningThreshold from 400 to a higher value (e.g., 600 or 800) to accommodate users with many open files.

Option B — Reduce per-model listeners (if the listener pattern should be optimized):
Fix location: src/vs/editor/contrib/semanticTokens/browser/documentSemanticTokens.ts → ModelSemanticColoring constructor
Approach: Instead of each ModelSemanticColoring subscribing individually to themeService.onDidColorThemeChange (line 178), have DocumentSemanticTokensFeature listen once and broadcast to all watchers — similar to how handleSettingOrThemeChange already works (line 52-64). This would reduce N per-model listeners to a single shared listener.

Recommended Owner

@bryanchen-d — author of PR #311728 that surfaced this bucket via leakWarningName, already assigned, best positioned to evaluate threshold vs. pattern fix.

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