[Unhandled Error] potential listener LEAK detected, popular — textModel / textFileEditorModel (file resolve, older)

[vs-code-engineering]

Error Message

potential listener LEAK detected, popular

Stack Trace

    at a.create (./src/vs/base/common/event.ts:1062:14)
    at LL._event [as event] (./src/vs/base/common/event.ts:1262:33)
    at LL.onFirstObserverAdded (./src/vs/base/common/observableInternal/observables/observableFromEvent.ts:95:28)
    at LL.addObserver (./src/vs/base/common/observableInternal/observables/baseObservable.ts:161:8)
    at Object.onWillAddFirstListener (./src/vs/base/common/event.ts:804:17)
    at G7e._event [as onDidChange] (./src/vs/base/common/event.ts:1271:19)
    at new ju (./src/vs/editor/common/model/textModel.ts:354:65)
    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 kJe._createModelData (./src/vs/editor/common/services/modelService.ts:310:54)
    at kJe.createModel (./src/vs/editor/common/services/modelService.ts:444:20)
    at v0.doCreateTextEditorModel (./src/vs/workbench/common/editor/textEditorModel.ts:172:0)
    at v0.createTextEditorModel (./src/vs/workbench/common/editor/textEditorModel.ts:166:0)
    at v0.doCreateTextModel (./src/vs/workbench/services/textfile/common/textFileEditorModel.ts:565:0)
    at v0.resolveFromContent (./src/vs/workbench/services/textfile/common/textFileEditorModel.ts:547:0)
    at v0.resolveFromFile (./src/vs/workbench/services/textfile/common/textFileEditorModel.ts:471:0)
    at async v0.resolve (./src/vs/workbench/services/textfile/common/textFileEditorModel.ts:307:0)
    at async w2e.doResolve (./src/vs/workbench/services/textfile/common/textFileEditorModelManager.ts:446:0)
    at async IJe.doCreateReferencedObject (./src/vs/workbench/services/textmodelResolver/common/textModelResolverService.ts:57:17)
    at async bSe.acquire (./src/vs/base/common/lifecycle.ts:727:18)

Raw Stack Trace (minified)

Error     at a.create (out/vs/workbench/workbench.desktop.main.js:403:18382)     at LL._event [as event] (out/vs/workbench/workbench.desktop.main.js:405:1807)     at LL.onFirstObserverAdded (out/vs/workbench/workbench.desktop.main.js:407:19306)     at LL.addObserver (out/vs/workbench/workbench.desktop.main.js:407:1590)     at Object.onWillAddFirstListener (out/vs/workbench/workbench.desktop.main.js:403:16116)     at G7e._event [as onDidChange] (out/vs/workbench/workbench.desktop.main.js:405:2074)     at new ju (out/vs/workbench/workbench.desktop.main.js:668:36700)     at a._createInstance (out/vs/workbench/workbench.desktop.main.js:1854:2000)     at a.createInstance (out/vs/workbench/workbench.desktop.main.js:1854:1440)     at kJe._createModelData (out/vs/workbench/workbench.desktop.main.js:1750:2487)     at kJe.createModel (out/vs/workbench/workbench.desktop.main.js:1751:898)     at v0.doCreateTextEditorModel (out/vs/workbench/workbench.desktop.main.js:936:14712)     at v0.createTextEditorModel (out/vs/workbench/workbench.desktop.main.js:936:14538)     at v0.doCreateTextModel (out/vs/workbench/workbench.desktop.main.js:1726:17779)     at v0.resolveFromContent (out/vs/workbench/workbench.desktop.main.js:1726:17616)     at v0.resolveFromFile (out/vs/workbench/workbench.desktop.main.js:1726:16718)     at async v0.resolve (out/vs/workbench/workbench.desktop.main.js:1726:14592)     at async w2e.doResolve (out/vs/workbench/workbench.desktop.main.js:5005:8805)     at async IJe.doCreateReferencedObject (out/vs/workbench/workbench.desktop.main.js:1726:27869)     at async bSe.acquire (out/vs/workbench/workbench.desktop.main.js:403:3866)     at async yJe.createModelReference (out/vs/workbench/workbench.desktop.main.js:1726:30165)     at async XEe._handleAsResourceInput (out/vs/workbench/workbench.desktop.main.js:967:11608)     at async XEe.$tryOpenDocument (out/vs/workbench/workbench.desktop.main.js:967:10864)

Details

Property	Value
Bucket ID	6dc284b6-1711-582d-2595-7931149f5644
Version	1.113.0
Commit	cfbea10c
Last Seen	Tue Mar 24 2026 23:59:27 GMT+0000 (Coordinated Universal Time)
Platforms	Windows, Linux, Mac
Product	VSCode

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This issue was automatically created from the VS Code Errors Dashboard

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Related Error Buckets

These additional error buckets are tracked by this issue (v1.113.0):

Bucket ID	Error Message	Hits	Users
5f282ff1-bb7c-b6ca-2aca-539c6cde016f	potential listener LEAK detected, dominated	492K	4.2K
29002e57-8eb1-2db0-7c8d-9b82b645a63b	potential listener LEAK detected, popular	446K	18.8K
1d8659c4-d5c4-bac7-7f2f-933c9aae2c36	potential listener LEAK detected, dominated	402K	2.7K
754b1f05-8fb5-553a-e5c4-bb66b581b329	potential listener LEAK detected, popular	394K	18.7K
733cfbc3-da69-256d-c039-8aa320a8256d	potential listener LEAK detected, popular	347K	19.4K

Generated by errors-triage · ◷

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Related Error Buckets

These additional error buckets are tracked by this issue (v1.113.0):

Bucket ID	Error Message	Version
8fd6841e	potential listener LEAK detected, popular	1.113.0
a6d1a856	potential listener LEAK detected, popular	1.113.0

Generated by errors-triage · ◷

[vs-code-engineering]

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
cacb6de3	potential listener LEAK detected, popular	1.114.0

Generated by errors-triage · ◷

[vs-code-engineering]

Related Error Buckets

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

Bucket ID	Error Message	Version
6bf751cc	potential listener LEAK detected, popular	1.114.0
18361d63	potential listener LEAK detected, popular	1.114.0
cacb6de3	potential listener LEAK detected, popular	1.114.0

Generated by errors-triage · ◷

[vs-code-engineering]

Related Error Buckets

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

Bucket ID	Error Message	Version
6bf751cc	potential listener LEAK detected, popular	1.114.0
18361d63	potential listener LEAK detected, popular	1.114.0
cacb6de3	potential listener LEAK detected, popular	1.114.0

Generated by errors-triage · ◷

[vs-code-engineering]

🔍 Error Investigation

Summary

The error "potential listener LEAK detected, popular" fires when the global LanguageService._onDidChange emitter exceeds its leakWarningThreshold of 200. Every TextModel created with an ILanguageSelection subscribes to this global emitter via a chain of wrappers (LanguageSelection.onDidChange → observableFromEvent → LanguageService.onDidChange). When a workspace has 200+ open models, the threshold is exceeded. This is a longstanding design issue — not a disposal bug — correctly classified as "popular" (many independent callers, no single dominant subscriber).

Impact: 3M+ hits, 121K+ users across all platforms.

Culprit Commit

Field	Value
Commit	18b02b6
Author	@jrieken
PR	#303543
Message	Classify listener leak errors as dominated or popular
Why	This commit added the "popular"/"dominated" suffix to ListenerLeakError messages, creating a new error bucket. The underlying listener accumulation on LanguageService._onDidChange is a pre-existing design issue (threshold already raised from default to 200 in #119968).

Note: The commit above created the error bucket (by changing the error message). The underlying listener accumulation pattern has existed since LanguageSelection was introduced.

Code Flow

sequenceDiagram
    participant Ext as Extension / Editor
    participant TFM as TextFileEditorModel
    participant MS as ModelService
    participant TM as TextModel
    participant LS as LanguageSelection
    participant OFE as observableFromEvent
    participant GE as LanguageService._onDidChange

    Ext->>TFM: resolve() → open file
    TFM->>MS: createModel(value, languageSelection)
    MS->>TM: new TextModel(languageSelection)
    Note over TM: textModel.ts:354<br/>subscribes to onDidChange
    TM->>LS: languageSelection.onDidChange(cb)
    LS->>OFE: Event.fromObservable → addObserver
    Note over OFE: observableFromEvent.ts:95<br/>onFirstObserverAdded
    OFE->>GE: subscribe to global event
    Note over GE: ⚠️ leakWarningThreshold: 200<br/>(languageService.ts:26)<br/>Exceeded when 200+ models exist
    Note over GE: 💥 ListenerLeakError("popular")<br/>fired via event.ts:1032

Loading

Affected Files

File	Role
src/vs/base/common/event.ts:1032	Crash site — LeakageMonitor.check() creates ListenerLeakError when threshold exceeded
src/vs/base/common/event.ts:1074-1087	ListenerLeakError class with "dominated"/"popular" kind
src/vs/editor/common/services/languageService.ts:26	Root cause — _onDidChange emitter with leakWarningThreshold: 200
src/vs/editor/common/services/languageService.ts:152-164	LanguageSelection class — creates per-instance observable wrapping global event
src/vs/editor/common/model/textModel.ts:354	Subscription site — each TextModel subscribes to languageSelection.onDidChange
src/vs/editor/common/services/modelService.ts:310	Model creation — _createModelData instantiates TextModel with ILanguageSelection

Repro Steps

1. Open VS Code with a large workspace (or use extensions that open many documents programmatically via vscode.workspace.openTextDocument)
2. Open 200+ files — each open file creates a TextModel with a LanguageSelection that subscribes to the global LanguageService.onDidChange
3. The 200th model triggers the leak warning. Extensions calling $tryOpenDocument (visible at the bottom of the raw stack) accelerate this.
4. The error is non-deterministic in the sense that it depends on how many models are simultaneously alive. Users with many tabs/editors or extensions that process many files are most likely to trigger it.

Fix Proposal

Two complementary approaches:

Option A — Raise the threshold (quick fix):
Fix location: src/vs/editor/common/services/languageService.ts → line 26
Approach: Increase leakWarningThreshold from 200 to a higher value (e.g., 500 or 1000). This was already raised once for #119968. Given that each open TextModel legitimately needs to listen for language changes, 200 is too low for modern workspaces with many open files.

Option B — Share subscriptions (architectural fix):
Fix location: src/vs/editor/common/services/languageService.ts → LanguageSelection class
Approach: Instead of each LanguageSelection instance independently subscribing to the global onDidChange event via its own observableFromEvent, use a single shared observable that all LanguageSelection instances reference. This would reduce the listener count on the global emitter from N (one per model) to 1 (shared), regardless of how many models exist.

Recommended Owner

@jrieken — Author of the leak detection classification change (PR #303543) and owner of the event infrastructure (src/vs/base/common/event.ts). Also the original author of ListenerLeakError (#212900). The threshold on LanguageService._onDidChange was previously tuned in response to #119968.

Generated by errors-investigate · ◷

[vs-code-engineering]

Related Error Buckets

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

Bucket ID	Error Message	Version
6bf751cc	potential listener LEAK detected, popular	1.114.0

Stack path: event.ts → observableFromEvent.ts → baseObservable.ts → event.ts → textModel.ts:354 → modelService.ts:310 — same observable/textModel listener leak pattern as the primary bucket.

Generated by errors-triage · ◷

[vs-code-engineering]

Related Error Buckets

These error buckets continue to appear in v1.115.0 (previously tracked since v1.114.0):

Bucket ID	Error Message	Version
6bf751cc	potential listener LEAK detected, popular	1.115.0

Generated by errors-triage · ● 3.7M · ◷