Microsoft/vscode

Review AsyncIterableObject usage: potential memory leaks and migration to AsyncIterableProducer

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#256854 opened on Jul 19, 2025

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 (19 comments) (0 reactions) (2 assignees)TypeScript (74,848 stars) (10,221 forks)batch import
debtgood first issuehelp wantedperf

Description

GitHub Issue: Review AsyncIterableObject usage: potential memory leaks and migration to AsyncIterableProducer

Title: Review AsyncIterableObject usage: potential memory leaks and migration to AsyncIterableProducer

Problem

AsyncIterableObject has a potential memory leak issue when iterables are only consumed once. The class stores all emitted values in an internal _results array to support multiple iterations, but this means values are never garbage collected in long-running iterations even when the iterable is only consumed once.

AsyncIterableProducer was introduced as an alternative that doesn't store values, making it more memory-efficient for single-consumption scenarios. However, this means that a second iteration will miss initial values.

Analysis

We found 112 occurrences of AsyncIterableObject across the codebase that should be reviewed to determine if they can be migrated to AsyncIterableProducer for better memory efficiency.

Action Items

Please review the usages you've contributed to and determine if they can be migrated to AsyncIterableProducer:

Contributors to Review

  • @alexdima (31 occurrences) - Core async.ts implementation and editor hover functionality
  • @jrieken (18 occurrences) - AsyncIterableSource, tests, chat and language model features
  • @aiday-mar (15 occurrences) - Editor hover functionality (inlay hints, color picker, markdown hover)
  • @amunger (19 occurrences total) - Notebook-related functionality and tests
  • @hediet (8 occurrences) - Core async functionality and inline completions
  • @Tyriar (5 occurrences) - Terminal shell integration
  • @sandy081 (4 occurrences) - Extension services
  • @joaomoreno (2 occurrences) - Workspace functionality
  • @connor4312 (2 occurrences) - MCP (Model Context Protocol) server
  • @aeschli (2 occurrences) - Chat code block operations
  • @DonJayamanne (1 occurrence) - Chat code block operations
  • @mjbvz (1 occurrence) - Editor hover functionality

Review Criteria

For each usage, consider:

  1. Single vs Multiple Consumption: Is the AsyncIterable consumed only once or multiple times?
  2. Memory Sensitivity: Are large amounts of data being emitted that should be garbage collected promptly?
  3. Performance Impact: Would switching to AsyncIterableProducer provide meaningful memory savings?

Migration Guidelines

✅ Good candidates for AsyncIterableProducer:

  • Single-use iterables (consumed once then discarded)
  • Large data streams
  • Real-time data processing
  • Event streams

❌ Keep AsyncIterableObject for:

  • Iterables that need to be consumed multiple times
  • Cases where re-iteration is expected

Files to Review

src/vs/base/common/async.ts

  • Lines: 1963, 1975, 1977, 1978, 1983, 1984, 1989, 1990, 1995, 1996, 2005, 2063, 2064, 2071, 2072, 2075, 2076, 2085, 2086, 2087, 2088, 2091, 2092, 2095, 2096, 2108, 2171, 2184, 2188, 2215, 2228, 2267, 2375

Hover functionality:

  • src/vs/editor/contrib/hover/browser/contentHoverComputer.ts (5 occurrences)
  • src/vs/editor/contrib/hover/browser/markdownHoverParticipant.ts (5 occurrences)
  • src/vs/editor/contrib/hover/browser/getHover.ts (3 occurrences)
  • src/vs/editor/contrib/hover/browser/hoverOperation.ts (3 occurrences)
  • src/vs/editor/contrib/hover/browser/hoverTypes.ts (2 occurrences)

Inlay hints:

  • src/vs/editor/contrib/inlayHints/browser/inlayHintsHover.ts (7 occurrences)

Other editor features:

  • src/vs/editor/contrib/inlineCompletions/browser/model/provideInlineCompletions.ts (3 occurrences)
  • src/vs/editor/contrib/colorPicker/browser/hoverColorPicker/hoverColorPickerParticipant.ts (3 occurrences)

Notebook functionality:

  • src/vs/workbench/contrib/notebook/test/browser/ (15 occurrences across test files)
  • src/vs/workbench/contrib/notebook/common/notebookKernelService.ts (2 occurrences)
  • src/vs/workbench/api/browser/mainThreadNotebookKernels.ts (3 occurrences)

Chat functionality:

  • src/vs/workbench/contrib/chat/browser/actions/chatCodeblockActions.ts (2 occurrences)
  • src/vs/workbench/contrib/chat/browser/actions/codeBlockOperations.ts (2 occurrences)
  • src/vs/workbench/services/extensions/browser/extensionService.ts (2 occurrences)
  • src/vs/workbench/services/extensions/electron-browser/nativeExtensionService.ts (2 occurrences)
  • src/vs/workbench/api/common/extHostTerminalShellIntegration.ts (4 occurrences)
  • src/vs/workbench/api/common/extHostLanguageModels.ts (2 occurrences)
  • src/vs/workbench/api/common/extHostWorkspace.ts (2 occurrences)
  • src/vs/workbench/contrib/mcp/common/mcpServer.ts (2 occurrences)

Next Steps

  1. Each contributor should review their assigned usages
  2. Create follow-up PRs for migrations where appropriate
  3. Update documentation/guidelines for when to use each class
  4. Consider adding ESLint rules to guide future usage

This review will help improve VS Code's memory efficiency and prevent potential memory leaks in async iteration scenarios.

Labels to add: debt, performance, good first issue, help wanted

Contributor guide

Tech stack
typescriptnodejs
Domain
performance
Issue type
refactor
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
TypeScriptasync/awaitasync iterablesVS Code codebase
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
Review the 112 occurrences of AsyncIterableObject in the listed files, such as src/vs/base/common/async.ts and editor hover features. For each, determine if the iterable is consumed only once (good for AsyncIterableProducer) or multiple times (keep AsyncIterableObject) based on the Review Criteria. Check the existing progress (checkboxes) to avoid duplication. Focus on files with many occurrences like core async.ts and editor hover.