memory-leak-audit

name memory-leak-audit description Audit code for memory leaks and disposable issues. Use when reviewing event listeners, DOM handlers, lifecycle callbacks, or fixing leak reports. Covers addDisposableListener, Event.once, MutableDisposable, DisposableStore, and onWillDispose patterns. Memory Leak Audit The #1 bug category in VS Code. This skill encodes the patterns that prevent and fix leaks. When to Use Reviewing code that registers event listeners or DOM handlers Fixing reported memory leaks (listener counts growing over time) Creating objects in methods that are called repeatedly Working with model lifecycle events (onWillDispose, onDidClose) Adding event subscriptions in constructors or setup methods Audit Checklist Work through each check in order. A single missed pattern can cause thousands of leaked objects. Step 1: DOM Event Listeners Rule : Never use raw .onload , .onclick , or addEventListener() directly. Always use addDisposableListener() . // BAD — leaks a listener every call this . iconElement . onload = () => { ... }; // GOOD — tracked and disposable this . _register ( addDisposableListener ( this . iconElement , 'load' , () => { ... })); Validated by : PR #280566 — Extension icon widget leaked 185 listeners after 37 toggles. Step 2: One-Time Events Rule : Use Event.once() for events that should only fire once (lifecycle events, close events, first-change events). // BAD — listener stays registered forever after first fire model. onDidDispose ( () => store. dispose ()); // GOOD — auto-removes after first invocation Event . once (model. onDidDispose )( () => store. dispose ()); Validated by : PRs #285657, #285661 — Terminal lifecycle hacks replaced with Event.once() . Step 3: Repeated Method Calls Rule : Objects created in methods called multiple times must NOT be registered to the class this._register() . Use MutableDisposable or return IDisposable to the caller. // BAD — every call adds another listener to the class store startSearch ( ) { this . _register ( this . model . onResults ( () => { ... })); } // GOOD — MutableDisposable ensures max 1 listener private readonly _searchListener = this . _register ( new MutableDisposable ()); startSearch ( ) { this . _searchListener . value = this . model . onResults ( () => { ... }); } When the event should only fire once per method call, combine Event.once() with MutableDisposable — this auto-removes the listener after the first invocation while still guarding against repeated calls: private readonly _searchListener = this . _register ( new MutableDisposable ()); startSearch ( ) { this . _searchListener . value = Event . once ( this . model . onResults )( () => { ... }); } Validated by : PR #283466 — Terminal find widget leaked 1 listener per search. Step 4: Model-Tied DisposableStores Rule : When creating a DisposableStore tied to a model's lifetime, register model.onWillDispose(() => store.dispose()) to the store itself. const store = new DisposableStore (); store. add (model. onWillDispose ( () => store. dispose ())); store. add (model. onDidChange ( () => { ... })); Validated by : Pattern used in chatEditingSession.ts , fileBasedRecommendations.ts , testingContentProvider.ts . Step 5: Resource Pool Patterns Rule : When using factory methods that create pooled objects (lists, trees), disposables must be registered to the individual item, not the pool class. // BAD — registers to pool, never cleaned per item createItem ( ) { const item = new Item (); this . _register (item. onEvent ( () => { ... })); return item; } // GOOD — wrap with item-scoped disposal createItem (): IDisposable & Item { const store = new DisposableStore (); const item = new Item (); store. add (item. onEvent ( () => { ... })); return { ...item, dispose : () => store. dispose () }; } Validated by : PR #290505 — Chat content parts CollapsibleListPool and TreePool leaked disposables. Step 6: Test Validation Rule : Every test suite that creates disposable objects must call ensureNoDisposablesAreLeakedInTestSuite() . import { ensureNoDisposablesAreLeakedInTestSuite } from '../../../../base/test/common/utils.js' ; suite ( 'MyFeature' , () => { ensureNoDisposablesAreLeakedInTestSuite (); test ( 'does something' , () => { // test disposables are tracked automatically }); }); Quick Reference Scenario Pattern Anti-Pattern DOM events addDisposableListener() .onclick = , addEventListener() One-time events Event.once(event)(handler) event(handler) for lifecycle Repeated methods MutableDisposable or return IDisposable this._register() in non-constructor Model lifecycle store.add(model.onWillDispose(...)) Forgetting cleanup Pooled objects Item-scoped DisposableStore Pool-scoped this._register() Tests ensureNoDisposablesAreLeakedInTestSuite() No leak checking Verification After fixing leaks, verify by: Checking listener counts before/after repeated operations Running ensureNoDisposablesAreLeakedInTestSuite() in tests Confirming object counts stabilize (don't grow linearly with usage) For chat-specific leaks : Run the chat memory leak checker via npm run perf:chat-leak (see the chat-perf skill). It sends N messages in a single session, forces GC between each, and uses linear regression on heap/DOM samples to detect per-message growth. A slope above 2 MB/msg indicates a leak. Use --messages 20 --verbose for more accurate results.