Promise memory leak when duplicating selection

[SimonSiefke]

Expected behaviour

When duplicating selected text and then deleting it again, the number of promises stays the same

Actual behaviour

When duplicating selected text and then deleting it, the number of promises increases each time. Duplicating selection 197 times in VS Code 1.105.1:

{
  "promisesWithStackTrace": [
    {
      "count": 394,
      "properties": [
        {
          "name": "[[PromiseState]]",
          "type": "string",
          "value": "pending"
        },
        {
          "name": "[[PromiseResult]]",
          "type": "undefined",
          "value": "undefined"
        }
      ],
      "originalStack": [
        "src/vs/editor/contrib/folding/browser/folding.ts:345:6",
        "src/vs/editor/contrib/folding/browser/folding.ts:301:7",
        "src/vs/editor/contrib/folding/browser/folding.ts:251:96",
        "src/vs/base/common/event.ts:1201:12",
        "src/vs/base/common/event.ts:1212:17",
        "src/vs/base/common/event.ts:1236:22",
        "src/vs/editor/browser/widget/codeEditor/codeEditorWidget.ts:1816:35",
        "src/vs/base/common/event.ts:1201:12"
      ]
    },
    {
      "count": 394,
      "properties": [
        {
          "name": "[[PromiseState]]",
          "type": "string",
          "value": "fulfilled"
        },
        {
          "name": "[[PromiseResult]]",
          "type": "undefined",
          "value": "undefined"
        }
      ],
      "originalStack": [
        "src/vs/workbench/contrib/comments/browser/commentsController.ts:710:6",
        "src/vs/workbench/contrib/comments/browser/commentsController.ts:939:9",
        "src/vs/base/common/event.ts:1201:12",
        "src/vs/base/common/event.ts:1212:17",
        "src/vs/base/common/event.ts:1236:22",
        "src/vs/editor/browser/widget/codeEditor/codeEditorWidget.ts:1816:35",
        "src/vs/base/common/event.ts:1201:12",
        "src/vs/base/common/event.ts:1232:17"
      ]
    },
    {
      "count": 197,
      "properties": [
        {
          "name": "[[PromiseState]]",
          "type": "string",
          "value": "fulfilled"
        },
        {
          "name": "[[PromiseResult]]",
          "type": "undefined",
          "value": "undefined"
        }
      ],
      "originalStack": [
        "src/vs/workbench/contrib/scm/browser/quickDiffModel.ts:232:10",
        "src/vs/editor/common/model/textModel.ts:243:87",
        "src/vs/base/common/event.ts:1201:12",
        "src/vs/base/common/event.ts:1212:17",
        "src/vs/base/common/event.ts:1236:22",
        "src/vs/editor/common/model/textModel.ts:2669:22",
        "src/vs/editor/common/model/textModel.ts:1432:22"
      ]
    },
    {
      "count": 197,
      "properties": [
        {
          "name": "[[PromiseState]]",
          "type": "string",
          "value": "fulfilled"
        },
        {
          "name": "[[PromiseResult]]",
          "type": "undefined",
          "value": "undefined"
        }
      ],
      "originalStack": [
        "src/vs/workbench/contrib/scm/browser/quickDiffModel.ts:232:10",
        "src/vs/editor/common/model/textModel.ts:243:87",
        "src/vs/base/common/event.ts:1201:12",
        "src/vs/base/common/event.ts:1212:17",
        "src/vs/base/common/event.ts:1236:22",
        "src/vs/editor/common/model/textModel.ts:2669:22",
        "src/vs/editor/common/model/textModel.ts:1301:22"
      ]
    }
  ]}

Based on the stack traces, it seems to show 4 promise memory leaks:

• one related to folding
• one related to commentsController
• two related to quickDiffModel

Additional information

Test script for leaked promises:

git clone git@github.com:SimonSiefke/vscode-memory-leak-finder.git &&
cd vscode-memory-leak-finder &&
npm ci &&
node packages/cli/bin/test.js --cwd packages/e2e   --only editor.duplicate-selection --runs 97 --check-leaks --measure promises-with-stack-trace --run-skipped-tests-anyway --measure-after &&
cat .vscode-memory-leak-finder-results/promises-with-stack-trace/editor.duplicate-selection.json

The script can also be run with a local vscode version by passing --vscode-version "/some/custom/path/to/vscode/scripts/code.sh".

Other

Does this issue occur when all extensions are disabled?: Yes

• VS Code Version: 1.105.1
• OS Version: Ubuntu 25.04

[alexr00]

Seems to be related to the use of the Delayer:

vscode/src/vs/base/common/async.ts

Lines 382 to 383 in 79a06da

	export class Delayer<T> implements IDisposable {

[alexr00]

I'm not seeing the number of promises grow in the comments controller. They seem to be getting garbage collected.

[aeschli]

Same for folding, I don't see anyone holding on promises. Can the finder print out the how the promises are still referenced?

[SimonSiefke]

Hi @alexr00 and @aeschli ,
Thanks for the feedback! I will look into it more...

For me it shows the results from above locally and in github codespaces (using the devcontainer and xvfb-run). Not sure what's going on.

Could of course also be something wrong with the test script where the promises and disposables are eventually disposed after some idle time - which would be fine of course and no leak.

Can the finder print out the how the promises are still referenced?

No. But I like that idea. Maybe I can implement it!

[aeschli]

Closing the issue as I don't see the leak