VSCode Memory Leak Finder

Find memory leaks in vscode to improve robustness and performance.

Quickstart

git clone git@github.com:SimonSiefke/vscode-memory-leak-finder.git &&
cd vscode-memory-leak-finder &&
npm ci &&
npm run e2e

Sharding

Split the selected test files across parallel jobs with the Jest-compatible, one-based --shard=<index>/<count> option:

node packages/cli/bin/test.js --cwd packages/e2e --measure promises-with-stack-trace --shard=1/2
node packages/cli/bin/test.js --cwd packages/e2e --measure promises-with-stack-trace --shard=2/2

Each test file belongs to exactly one shard. Results from separate jobs can be downloaded into directories whose names start with vscode-memory-leak-finder-results-linux- and combined with:

node packages/build/src/mergeArtifacts.ts

Measures

PendingPromisesWithRetainers

Finds pending Promises added during a test and reports their shortest strong path from a GC root, together with per-path counts and retained bytes. Inspector query handles are released before the final heap snapshot.

node packages/cli/bin/test.js --cwd packages/e2e --check-leaks --measure-after --measure pending-promises-with-retainers --only base

RetainedBytesBySource

Ranks allocation sources by the bytes they still own after garbage collection. Source-map-aware results include surviving allocation count, dominated object count, and retained bytes.

node packages/cli/bin/test.js --cwd packages/e2e --check-leaks --measure-after --measure retained-bytes-by-source --only base

NativeContextCount

Measures live V8 native contexts from before and after heap snapshots. A growing count can reveal leaked windows, workers, realms, or VM contexts.

node packages/cli/bin/test.js --cwd packages/e2e --check-leaks --measure-after --measure native-context-count --only base

ActiveAsyncResourcesWithStackTraces

Tracks Node async resources created during the test and reports resources that remain active, grouped by resource type and creation stack. The tracker stores metadata only and removes its hook during capture.

node packages/cli/bin/test.js --cwd packages/e2e --check-leaks --measure-after --measure active-async-resources-with-stack-traces --only base

ObjectShapeDifference

Compares V8 object shapes before and after a test. Results identify constructor, prototype, elements kind, descriptor names, shape-count delta, and live-instance delta.

node packages/cli/bin/test.js --cwd packages/e2e --check-leaks --measure-after --measure object-shape-difference --only base

ObjectUrlCount

Spies on URL.createObjectURL and URL.revokeObjectURL from renderer startup and reports cumulative call counts plus the number of created object URLs that are still active after each test.

node packages/cli/bin/test.js --cwd packages/e2e --check-leaks --measure-after --measure object-url-count --only base

MemoryCity

Captures allocation-aware renderer and extension-host heap snapshots, computes source-mapped retained ownership, and generates the interactive VS Code Memory City visualization.

node packages/cli/bin/test.js --cwd packages/e2e --check-leaks --measure-after --measure memory-city --only base

Build or preview the standalone viewer:

npm --prefix packages/visualizations run build
npm --prefix packages/visualizations run dev

ChromiumMemoryDump

Captures two detailed Chromium MemoryInfra snapshots around a browser scenario. The informational result compares per-process private footprint and detailed allocator paths, retains normalized allocator attributes and ownership edges, and reports trace completeness without storing the full raw trace. Because allocator paths are hierarchical, their sizes are not additive.

node packages/cli/bin/test.js --cwd packages/e2e --check-leaks --measure-after --measure chromium-memory-dump --only base
npm run build-charts

The generated process and allocator charts are written to .vscode-charts/chromium-memory-dump-processes and .vscode-charts/chromium-memory-dump-allocators.

ArrayBufferBytes

Measures the native backing-store bytes retained by live ArrayBuffer objects. The result includes before, after, and delta byte and backing-store counts.

node packages/cli/bin/test.js --cwd packages/e2e --check-leaks --measure-after --measure array-buffer-bytes --only base

PerformanceMarkCounts

Measures the number of native Chromium PerformanceMark objects before and after a browser scenario. The generated chart shows the initial count in black and growth in red.

node packages/cli/bin/test.js --cwd packages/e2e --check-leaks --measure-after --measure performance-mark-counts --only base
npm run build-charts

PerformanceMarkBytes

Measures the native self-size bytes retained by Chromium PerformanceMark objects before and after a browser scenario. The generated chart shows the initial bytes in black and growth in red.

node packages/cli/bin/test.js --cwd packages/e2e --check-leaks --measure-after --measure performance-mark-bytes --only base
npm run build-charts

ArrayCount

Measures the total number of arrays.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure array-count --only base

ArrayElementCount

Measures the total number of elements in all arrays.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure array-element-count --only base

ClassCount

Measures the total number of classes.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure class-count --only base

CompiledCodeSize

Measures V8 compiled-code bytes from before and after heap snapshots. Results include the exact total, attributed/shared/unattributed buckets, and rankings by function size and growth.

node packages/cli/bin/test.js --cwd packages/e2e --measure-after --measure compiled-code-size --only base

ConcatenatedErrorStringCount

Measures V8 concatenated-string nodes whose bounded prefix is an Error-style stack trace. The result includes before/after matching counts and diagnostic totals for all concatenated strings; stack contents are not written to the result.

node packages/cli/bin/test.js --cwd packages/e2e --check-leaks --measure-after --measure concatenated-error-string-count --only base

ConcatenatedStrings

Measures V8 concatenated-string nodes and reconstructs their values when the heap snapshot contains enough rope data. The before/after data is an array of strings, with V8's node name used when a value cannot be reconstructed.

node packages/cli/bin/test.js --cwd packages/e2e --check-leaks --measure-after --measure concatenated-strings --only base

CpuPerformanceCounters

Measures CPU instructions and cycles for the inspected process.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure cpu-performance-counters --only base

LinuxProcessTreeResources

On Linux, measures CPU activity and aggregate proportional memory for the Electron main process and its descendants during the scenario. CPU data comes from inherited perf stat counters. Memory data comes from the sum of /proc/<pid>/smaps_rollup PSS sampled every 250 ms, so sampledPeakPssMiB can miss shorter spikes. The result is informational and never reports a leak.

node packages/cli/bin/test.js --cwd packages/e2e --measure-after --measure linux-process-tree-resources --only base

LinuxProcessTreeResourcesFromStart

Measures the same process-tree resources from Electron launch through scenario completion. Use --startup-runs to restart Electron and aggregate every numeric metric across independent samples.

node packages/cli/bin/test.js --cwd packages/e2e --measure-after --measure linux-process-tree-resources-from-start --startup-runs 5 --only base

Both measures run collection and parsing in a dedicated Linux process-tree worker. The caller starts it with the process-tree root PID, receives the parsed result when stopping it, and disposes the worker immediately after measurement. They require Linux, perf, access to the requested perf events, and readable smaps_rollup files. Missing facilities or permissions fail the measure instead of producing zero-valued counters. GNU time is intentionally not used because its maximum RSS is not the simultaneous sum of Electron's processes.

DetachedDomNodeCount

Measures the total number of detached dom nodes.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure detached-dom-node-count --only base

DomCounters

Measures dom nodes, jsEventListeners and documents.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure dom-counters --only base

DomNodeCount

Measures the total number of dom nodes.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure dom-node-count --only base

DuplicatedStrings

Measures flat string values represented by more than one V8 heap node. Each duplicated value occurs once in the before/after string arrays.

node packages/cli/bin/test.js --cwd packages/e2e --check-leaks --measure-after --measure duplicated-strings --only base

EditContextCount

Measures the total number of edit context.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure edit-context-count --only base

EventListenerCount

Measures the total number of event listeners.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure event-listener-count --only base

EventListeners

Measures the event listeners.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure event-listeners --only base

FinalizationRegistryCount

Measures the total number of live FinalizationRegistry instances.

node packages/cli/bin/test.js --cwd packages/e2e --check-leaks --measure-after --measure finalization-registry-count --only base

FunctionCount

Measures the total number of functions.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure function-count --only base

GlobalLexicalScopeNames

Measures global variables / global lexical scope names.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure global-lexical-scope-names --only base

GlobalPropertyDifference

Reports own string-named properties added to globalThis during the measured scenario. Global lexical bindings are covered separately by global-lexical-scope-names.

node packages/cli/bin/test.js --cwd packages/e2e --check-leaks --measure-after --measure global-property-difference --only base

HeapUsage

Measures heap usage.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure heap-usage --only base

InstanceCounts

Measures the number of instances of each class.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure instance-counts --only base

IntersectionObserverCount

Measures the number of intersection observers.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure intersection-observer-count --only base

MapSize

Measures the total number of elements in all Maps.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure map-size --only base

MediaQueryListCount

Measures the total number of MediaQueryLists.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure media-query-list-count --only base

MutationObserverCount

Measures the total number of MutationObservers.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure mutation-observer-count --only base

NamedFunctionCount

Measures the count of each function.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure named-function-count --only base

NamedFunctionDifference

Measures the difference in counts of each function.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure named-function-difference --only base

PromiseCount

Measures the total number of Promises.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure promise-count --only base

RegexCount

Measures the total number of Regex instances.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure regex-count --only base

ResizeObserverCount

Measures the total number of ResizeObservers.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure resize-observer-count --only base

SetSize

Measures the total number of elements in all Sets.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure set-size --only base

SetTimeout

Measures the total number of Timeouts.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure set-timeout --only base

TrackedTimeouts

Measures active timeouts using workbench instrumentation installed at application startup.

node packages/cli/bin/test.js --cwd packages/e2e --runs 1 --measure-after --measure tracked-timeouts --timeout-between 5000 --only base

TrackedAllocationLeaks

Reports allocation sites that retain instances after forced garbage collection. Results are informational potential leak candidates.

node packages/cli/bin/test.js --cwd packages/e2e --measure tracked-allocation-leaks --only editor-open

TrackedAllocationPerformance

Correlates allocation churn with sampled JavaScript CPU self-time by source file. The CPU percentage describes the source file, not the cost of allocation itself.

node packages/cli/bin/test.js --cwd packages/e2e --measure tracked-allocation-performance --only editor-type-many-characters

V8TurbofanStats

Measures V8 TurboFan optimization and deoptimization activity.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure v8-turbofan-stats --only base

WeakMapCount

Measures the total number of WeakMaps.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure weak-map-count --only base

WeakSetCount

Measures the total number of WeakSets.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure weak-set-count --only base

WindowCount

Measures the total number of Windows.

node packages/cli/bin/test.js --cwd packages/e2e  --check-leaks --measure-after --measure window-count --only base

Project Structure

• packages/charts: Visualizations for test output
• packages/cli: Command Line Interface, similar to jest
• packages/devtools-protocol: Functionality related to Chrome Devtools Protocol
• packages/e2e: The e2e test scenarios
• packages/file-watcher-worker: Watch files for changes
• packages/injected-code: Code injected to the page for e2e tests
• packages/memory-leak-finder: Library for finding memory leaks
• packages/memory-leak-worker: Process for finding memory leaks (uses the library from above)
• packages/page-object: Page Object Model to simplify e2e tests
• packages/source-map-worker: Functions for querying original positions and function names using source maps
• packages/test-coordinator: Determines which tests to run, launches VSCode, file-watcher-worker, test-worker, memory-leak-worker, video-recording-worker
• packages/test-worker: Runs tests
• packages/visualizations: Interactive source-mapped memory visualizations
• packages/test-worker-commands: Functions used by test-worker
• packages/video-recording-worker: Record screencasts of the tests

How does it work

Before and after a test is executed, all event listeners are queried using Chrome Devtools Protocol Runtime.queryObjects({ prototypeId: "EventTarget.prototype" }) and DomDebugger.getEventListeners.

We get an array of event listeners before and after, for example

// before
[
  {
    "type": "focusin",
    "description": "()=>this.j()",
    "objectId": "524841679309534768.4.2930",
    "stack": [
      "listener (file:///home/simon/.cache/repos/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.83.1/resources/app/out/vs/workbench/workbench.desktop.main.js:148:37007)",
    ],
    "sourceMaps": [
      "https://ticino.blob.core.windows.net/sourcemaps/f1b07bd25dfad64b0167beb15359ae573aecd2cc/core/vs/workbench/workbench.desktop.main.js.map",
    ],
  },
]

and

// after
[
  {
    "type": "focusin",
    "description": "()=>this.j()",
    "objectId": "524841679309534768.4.2930",
    "stack": [
      "listener (file:///home/simon/.cache/repos/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.83.1/resources/app/out/vs/workbench/workbench.desktop.main.js:148:37007)",
    ],
    "sourceMaps": [
      "https://ticino.blob.core.windows.net/sourcemaps/f1b07bd25dfad64b0167beb15359ae573aecd2cc/core/vs/workbench/workbench.desktop.main.js.map",
    ],
  },
  {
    "type": "keydown",
    "description": "N=>{new P.$qO(N).equals(2)&&N.preventDefault()}",
    "objectId": "3680313440875909344.4.4572",
    "stack": [
      "listener (file:///home/simon/.cache/repos/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.83.1/resources/app/out/vs/workbench/workbench.desktop.main.js:244:39878)",
    ],
    "sourceMaps": [
      "https://ticino.blob.core.windows.net/sourcemaps/f1b07bd25dfad64b0167beb15359ae573aecd2cc/core/vs/workbench/workbench.desktop.main.js.map",
    ],
    "originalStack": ["/src/vs/base/browser/ui/menu/menu.ts:122:58"],
  },
]

The before and after arrays are compared to see which event listeners have been added. In the example above, there is one keydown listener more in the after array which is not in the before array.

The tests are structured in a way one would be expect that the number of event listeners before and after the test are equal. For example, when opening and closing the menu, one would expect the number of event listeners stays equal. This is the menu toggle test:

// title-bar-menu-toggle.js
export const run = async ({ TitleBar }) => {
  await TitleBar.showMenuFile()
  await TitleBar.hideMenuFile()
}

Every time the test was executed, event listeners increased by one keydown listener in /src/vs/base/browser/ui/menu/menu.ts:122:58, which indicates a memory leak and in this case was precisely the location of the memory leak.

In other cases, the output for memory leaks might not be quite as clear, but maybe still helpful. This is the output for the notebook-open test (opening and closing a notebook):

[
  {
    "type": "contextmenu",
    "description": "n=>{t.$_O.stop(n,!0)}",
    "objectId": "2723967474668247540.4.13637",
    "stack": [
      "listener (file:///home/simon/.cache/repos/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.83.1/resources/app/out/vs/workbench/workbench.desktop.main.js:244:18357)"
    ],
    "sourceMaps": [
      "https://ticino.blob.core.windows.net/sourcemaps/f1b07bd25dfad64b0167beb15359ae573aecd2cc/core/vs/workbench/workbench.desktop.main.js.map"
    ],
    "count": 1,
    "originalStack": ["/src/vs/base/browser/ui/actionbar/actionbar.ts:370:117"]
  },
  {
    "type": "-monaco-gesturetap",
    "description": "r=>this.onClick(r,!0)",
    "objectId": "2723967474668247540.4.13695",
    "stack": [
      "listener (file:///home/simon/.cache/repos/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.83.1/resources/app/out/vs/workbench/workbench.desktop.main.js:244:10198)"
    ],
    "sourceMaps": [
      "https://ticino.blob.core.windows.net/sourcemaps/f1b07bd25dfad64b0167beb15359ae573aecd2cc/core/vs/workbench/workbench.desktop.main.js.map"
    ],
    "count": 1,
    "originalStack": ["/src/vs/base/browser/ui/actionbar/actionViewItems.ts:121:68"]
  },
  {
    "type": "mousedown",
    "description": "r=>{c||I.$_O.stop(r,!0),this._action.enabled&&r.button===0&&o.classList.add(\"active\")}",
    "objectId": "2723967474668247540.4.13697",
    "stack": [
      "listener (file:///home/simon/.cache/repos/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.83.1/resources/app/out/vs/workbench/workbench.desktop.main.js:244:10258)"
    ],
    "sourceMaps": [
      "https://ticino.blob.core.windows.net/sourcemaps/f1b07bd25dfad64b0167beb15359ae573aecd2cc/core/vs/workbench/workbench.desktop.main.js.map"
    ],
    "count": 1,
    "originalStack": ["/src/vs/base/browser/ui/actionbar/actionViewItems.ts:123:70"]
  },
  {
    "type": "click",
    "description": "r=>{I.$_O.stop(r,!0),this.m&&this.m.isMenu||this.onClick(r)}",
    "objectId": "2723967474668247540.4.13699",
    "stack": [
      "listener (file:///home/simon/.cache/repos/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.83.1/resources/app/out/vs/workbench/workbench.desktop.main.js:244:10475)"
    ],
    "sourceMaps": [
      "https://ticino.blob.core.windows.net/sourcemaps/f1b07bd25dfad64b0167beb15359ae573aecd2cc/core/vs/workbench/workbench.desktop.main.js.map"
    ],
    "count": 1,
    "originalStack": ["/src/vs/base/browser/ui/actionbar/actionViewItems.ts:145:65"]
  },
  {
    "type": "dblclick",
    "description": "r=>{I.$_O.stop(r,!0)}",
    "objectId": "2723967474668247540.4.13701",
    "stack": [
      "listener (file:///home/simon/.cache/repos/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.83.1/resources/app/out/vs/workbench/workbench.desktop.main.js:244:10572)"
    ],
    "sourceMaps": [
      "https://ticino.blob.core.windows.net/sourcemaps/f1b07bd25dfad64b0167beb15359ae573aecd2cc/core/vs/workbench/workbench.desktop.main.js.map"
    ],
    "count": 1,
    "originalStack": ["/src/vs/base/browser/ui/actionbar/actionViewItems.ts:154:68"]
  },
  {
    "type": "mouseout",
    "description": "n=>{I.$_O.stop(n),o.classList.remove(\"active\")}",
    "objectId": "2723967474668247540.4.13705",
    "stack": [
      "listener (file:///home/simon/.cache/repos/vscode-memory-leak-finder/.vscode-test/vscode-linux-x64-1.83.1/resources/app/out/vs/workbench/workbench.desktop.main.js:244:10662)"
    ],
    "sourceMaps": [
      "https://ticino.blob.core.windows.net/sourcemaps/f1b07bd25dfad64b0167beb15359ae573aecd2cc/core/vs/workbench/workbench.desktop.main.js.map"
    ],
    "count": 2,
    "originalStack": ["/src/vs/base/browser/ui/actionbar/actionViewItems.ts:159:56"]
  }
]

It seems there is memory leak when opening and closing a notebook. But just looking at the output, it's difficult to say much more. It's not clear where exactly the memory leak is and one might need to look more closely at the actionbar.ts and actionViewItems.ts code.

Memory Leaks

Component	Issue	Status
Menu	microsoft/vscode#195580	Fixed
Dropdown	microsoft/vscode#197767	Fixed
MenuBar	microsoft/vscode#198051	Fixed
DefaultWorkerFactory	microsoft/vscode#198709	Fixed
ExtensionList	microsoft/vscode#198709	Fixed
SimpleFindWidget	microsoft/vscode#199043	Fixed
ColorPickerWidget	microsoft/vscode#199814	Fixed
DiffEditor	microsoft/vscode#200381	Fixed
QuickPick	microsoft/vscode#201320	Fixed
Terminal	xtermjs/xterm.js#4935	Fixed
KeyBindingsEditor	microsoft/vscode#202455	Fixed
NotebookEditorWidget	microsoft/vscode#204756	Fixed
SettingsEditor2	microsoft/vscode#216763	Fixed
SettingEnumRenderer	microsoft/vscode#216855	Fixed
GettingStarted	microsoft/vscode#216858	Fixed
ExtensionTabs	microsoft/vscode#219726	Fixed
Output	microsoft/vscode#221605	Fixed
StickyScroll	microsoft/vscode#221622	Fixed
SelectBox	microsoft/vscode#221507	Fixed
DebugView	microsoft/vscode#225334	Fixed
SettingsIndicators	microsoft/vscode#236417	Fixed

Credits

This project is based on the jest cli, playwright and fuite.