fix: do not block indefinitely on thumbnails in desktopCapturer by ckerr · Pull Request #51128 · electron/electron

ckerr · 2026-04-17T15:18:46Z

Description of Change

Fixes #51125.
Fixes #51124.

Fixes a desktopCapturer regression introduced in dad4ab6. Only affects main.

Checklist

I have built and tested this change
I have filled out the PR description
I have reviewed and verified the changes
npm test passes
PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Fixed desktopCapturer.getSources() hanging on macOS.

nikwen · 2026-04-17T16:07:07Z

The Fiddle gist works for me on this patch.

e test -g desktopCapturer almost works for me:

ok 1 desktopCapturer should return a non-empty array of sources
ok 2 desktopCapturer throws an error for invalid options
ok 3 desktopCapturer does not throw an error when called more than once (regression)
ok 4 desktopCapturer responds to subsequent calls of different options
ok 5 desktopCapturer returns an empty display_id for window sources
not ok 6 desktopCapturer returns display_ids matching the Screen API
  expected '3' to equal '1'
  AssertionError: expected '3' to equal '1'
      at Context.<anonymous> (electron/spec/api-desktop-capturer-spec.ts:65:36)
not ok 7 desktopCapturer enabling thumbnail should return non-empty images
  expected false to be true
  AssertionError: expected false to be true
      at Context.<anonymous> (electron/spec/api-desktop-capturer-spec.ts:84:61)
ok 8 desktopCapturer disabling thumbnail should return empty images
ok 9 desktopCapturer getMediaSourceId should match DesktopCapturerSource.id
ok 10 desktopCapturer getSources should not incorrectly duplicate window_id
ok 11 desktopCapturer does not affect window resizable state
ok 12 desktopCapturer moveAbove should move the window at the requested place
ok 13 screen module screen.getAllDisplays returns displays with IDs matching desktopCapturer source display IDs

The first failure is due to having external screens connected. That's unrelated.

The second failure also happens for me on Electron 41.2.0. It's my password manager that won't let Electron record its window.

nikwen · 2026-04-17T16:20:09Z

Hm, we're still getting test failures in CI:

Logs

Failure in test: "desktopCapturer should return a non-empty array of sources"
Error: Timeout of 30000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/Users/runner/work/electron/electron/src/electron/spec/api-desktop-capturer-spec.ts)
    at createTimeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/errors.js:498:15)
    at Test.Runnable._timeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/runnable.js:429:10)
Retrying test (1/3)...
Failure in test: "desktopCapturer should return a non-empty array of sources"
Error: Timeout of 30000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/Users/runner/work/electron/electron/src/electron/spec/api-desktop-capturer-spec.ts)
    at createTimeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/errors.js:498:15)
    at Test.Runnable._timeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/runnable.js:429:10)
Retrying test (2/3)...
Failure in test: "desktopCapturer should return a non-empty array of sources"
Error: Timeout of 30000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/Users/runner/work/electron/electron/src/electron/spec/api-desktop-capturer-spec.ts)
    at createTimeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/errors.js:498:15)
    at Test.Runnable._timeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/runnable.js:429:10)
Retrying test (3/3)...
not ok 105 desktopCapturer should return a non-empty array of sources
  Timeout of 30000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/Users/runner/work/electron/electron/src/electron/spec/api-desktop-capturer-spec.ts)
  Error: Timeout of 30000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/Users/runner/work/electron/electron/src/electron/spec/api-desktop-capturer-spec.ts)
      at listOnTimeout (node:internal/timers:605:17)
      at processTimers (node:internal/timers:541:7)
ok 106 desktopCapturer throws an error for invalid options
Failure in test: "desktopCapturer does not throw an error when called more than once (regression)"
Error: Timeout of 30000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/Users/runner/work/electron/electron/src/electron/spec/api-desktop-capturer-spec.ts)
    at createTimeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/errors.js:498:15)
    at Test.Runnable._timeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/runnable.js:429:10)
Retrying test (1/3)...
Failure in test: "desktopCapturer does not throw an error when called more than once (regression)"
Error: Timeout of 30000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/Users/runner/work/electron/electron/src/electron/spec/api-desktop-capturer-spec.ts)
    at createTimeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/errors.js:498:15)
    at Test.Runnable._timeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/runnable.js:429:10)
Retrying test (2/3)...
Failure in test: "desktopCapturer does not throw an error when called more than once (regression)"
Error: Timeout of 30000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/Users/runner/work/electron/electron/src/electron/spec/api-desktop-capturer-spec.ts)
    at createTimeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/errors.js:498:15)
    at Test.Runnable._timeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/runnable.js:429:10)
Retrying test (3/3)...
not ok 107 desktopCapturer does not throw an error when called more than once (regression)
  Timeout of 30000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/Users/runner/work/electron/electron/src/electron/spec/api-desktop-capturer-spec.ts)
  Error: Timeout of 30000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/Users/runner/work/electron/electron/src/electron/spec/api-desktop-capturer-spec.ts)
      at listOnTimeout (node:internal/timers:605:17)
      at processTimers (node:internal/timers:541:7)
Failure in test: "desktopCapturer responds to subsequent calls of different options"
Error: Timeout of 30000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/Users/runner/work/electron/electron/src/electron/spec/api-desktop-capturer-spec.ts)
    at createTimeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/errors.js:498:15)
    at Test.Runnable._timeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/runnable.js:429:10)
Retrying test (1/3)...
Failure in test: "desktopCapturer responds to subsequent calls of different options"
Error: Timeout of 30000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/Users/runner/work/electron/electron/src/electron/spec/api-desktop-capturer-spec.ts)
    at createTimeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/errors.js:498:15)
    at Test.Runnable._timeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/runnable.js:429:10)
Retrying test (2/3)...
Failure in test: "desktopCapturer responds to subsequent calls of different options"
Error: Timeout of 30000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/Users/runner/work/electron/electron/src/electron/spec/api-desktop-capturer-spec.ts)
    at createTimeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/errors.js:498:15)
    at Test.Runnable._timeoutError (/Users/runner/work/electron/electron/src/electron/spec/node_modules/mocha/lib/runnable.js:429:10)
Retrying test (3/3)...
not ok 108 desktopCapturer responds to subsequent calls of different options
  Timeout of 30000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/Users/runner/work/electron/electron/src/electron/spec/api-desktop-capturer-spec.ts)
  Error: Timeout of 30000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/Users/runner/work/electron/electron/src/electron/spec/api-desktop-capturer-spec.ts)
      at listOnTimeout (node:internal/timers:605:17)
      at processTimers (node:internal/timers:541:7)
ok 109 desktopCapturer returns an empty display_id for window sources
ok 110 desktopCapturer returns display_ids matching the Screen API
ok 111 desktopCapturer enabling thumbnail should return non-empty images
ok 112 desktopCapturer disabling thumbnail should return empty images
ok 113 desktopCapturer getMediaSourceId should match DesktopCapturerSource.id
ok 114 desktopCapturer getSources should not incorrectly duplicate window_id
ok 115 desktopCapturer does not affect window resizable state
ok 116 desktopCapturer moveAbove should move the window at the requested place

fixes dad4ab6 regression

nikwen · 2026-04-17T19:14:58Z

Local test results on the most recent commit:

ok 1 desktopCapturer should return a non-empty array of sources
ok 2 desktopCapturer throws an error for invalid options
ok 3 desktopCapturer does not throw an error when called more than once (regression)
ok 4 desktopCapturer responds to subsequent calls of different options
ok 5 desktopCapturer returns an empty display_id for window sources
not ok 6 desktopCapturer returns display_ids matching the Screen API
  expected '3' to equal '1'
  AssertionError: expected '3' to equal '1'
      at Context.<anonymous> (electron/spec/api-desktop-capturer-spec.ts:65:36)
not ok 7 desktopCapturer enabling thumbnail should return non-empty images
  expected false to be true
  AssertionError: expected false to be true
      at Context.<anonymous> (electron/spec/api-desktop-capturer-spec.ts:84:61)
ok 8 desktopCapturer disabling thumbnail should return empty images
ok 9 desktopCapturer getMediaSourceId should match DesktopCapturerSource.id
ok 10 desktopCapturer getSources should not incorrectly duplicate window_id
ok 11 desktopCapturer does not affect window resizable state
ok 12 desktopCapturer moveAbove should move the window at the requested place
ok 13 screen module screen.getAllDisplays returns displays with IDs matching desktopCapturer source display IDs
# tests 13
# pass 11
# fail 2

I do notice that when I have my password manager open, tests take a lot longer to run now, given the 3-second timeout. (Maybe that's something we have to accept.)

chore: remove unnecessary code

nikwen · 2026-04-17T20:16:55Z

The mas tests ran through successfully!

ok 105 desktopCapturer should return a non-empty array of sources
ok 106 desktopCapturer throws an error for invalid options
ok 107 desktopCapturer does not throw an error when called more than once (regression)
ok 108 desktopCapturer responds to subsequent calls of different options
ok 109 desktopCapturer returns an empty display_id for window sources
ok 110 desktopCapturer returns display_ids matching the Screen API
ok 111 desktopCapturer enabling thumbnail should return non-empty images
ok 112 desktopCapturer disabling thumbnail should return empty images
ok 113 desktopCapturer getMediaSourceId should match DesktopCapturerSource.id
ok 114 desktopCapturer getSources should not incorrectly duplicate window_id
ok 115 desktopCapturer does not affect window resizable state
ok 116 desktopCapturer moveAbove should move the window at the requested place
ok 117 desktopCapturer fetchWindowIcons should find the test window in the list of captured sources
ok 118 desktopCapturer fetchWindowIcons should return a non-null appIcon for the captured window
ok 119 desktopCapturer fetchWindowIcons should return an appIcon that is not an empty image
ok 120 desktopCapturer fetchWindowIcons should return an appIcon that encodes to a valid PNG data URL
ok 121 desktopCapturer fetchWindowIcons should return an appIcon with dimensions greater than 0x0 pixels

nikwen

Just reviewed the code. Looks good to me! 👍

Co-authored-by: Niklas Wenzel <dev@nikwen.de>

ckerr · 2026-04-18T13:23:46Z

@nikwen thanks for all the feedback, it was a great help!

nikwen · 2026-04-18T23:20:15Z

@ckerr Thanks for working on it! If you could merge it, I'd appreciate that.

release-clerk · 2026-04-19T18:48:41Z

Release Notes Persisted

Fixed desktopCapturer.getSources() hanging on macOS.

* fix: timing issue DCHECK crash in DesktopCapturer on macOS (#50960) refactor: use StartUpdating in desktopCapturer Replace the one-shot Update() callback model with the continuous StartUpdating() observer model for NativeDesktopMediaList. Fixes a macOS DCHECK(can_refresh()) crash in UpdateSourceThumbnail(), where ScreenCaptureKit's recurrent thumbnail capturer would post UpdateSourceThumbnail callbacks after the one-shot refresh_callback_ had been consumed. Now, can_refresh() is always true because refresh_callback_ is repopulated via ScheduleNextRefresh(). Each capturer (window, screen) gets its own ListObserver that tracks readiness via OnSourceAdded and OnSourceThumbnailChanged events. Once a list has both sources and thumbnails (or thumbnails aren't requested), its data is snapshotted and the capturer checks if all requested types are ready before resolving to JS. Also remove the "skip_next_refresh_" Chromium patch, which was a workaround for the timing mismatch between the one-shot Update() model and ScreenCaptureKit's asynchronous thumbnail delivery. refactor: simplify state logic in DesktopCapturer (cherry picked from commit dad4ab6) * fix: do not block indefinitely on thumbnails in desktopCapturer (#51128) * fix: do not block indefinitely on thumbnails in desktopCapturer fixes dad4ab6 regression * fix: build error * fixup! fix: do not block indefinitely on thumbnails in desktopCapturer chore: remove unnecessary code * Update shell/browser/api/electron_api_desktop_capturer.cc Co-authored-by: Niklas Wenzel <dev@nikwen.de> --------- Co-authored-by: Niklas Wenzel <dev@nikwen.de> (cherry picked from commit a1d28e6) * fix: dangling `raw_ptr` regression in `DesktopCapturer` (#51158) fix: dangling raw_ptr in desktopCapturer (cherry picked from commit bef68b6) * fix: do not pass a `DesktopMediaList* to DesktopCapturer::OnListReady()` (#51399) refactor: do not pass a DesktopMediaList* to DesktopCapturer::OnListReady() The list pointer was being used as a proxy for its type, so just pass the type instead. This solves a lifecycle issue occurring in CI where the callack can outlive the DesktopMediaList. Sample error log: [48471:0428/193441.269750:FATAL:base/allocator/partition_alloc_support.cc:798] Detected dangling raw_ptr in unretained with id=0x0000013c02e14378: Task trace: 0 Electron Framework 0x000000012283a0ba electron::api::DesktopCapturer::ListObserver::MaybeNotifyReady() + 170 1 Electron Framework 0x0000000133246dc5 NativeDesktopMediaList::Worker::OnRecurrentCaptureResult(webrtc::DesktopCapturer::Result, std::__Cr::unique_ptr<webrtc::DesktopFrame, std::__Cr::default_delete<webrtc::DesktopFrame>>, long) + 357 2 Electron Framework 0x000000013328dbcf (anonymous namespace)::ScreenshotManagerCapturer::OnRecurrentCaptureTimer() + 1343 Stack trace: 0 Electron Framework 0x000000012ade42f2 base::debug::CollectStackTrace(base::span<void const*, 18446744073709551615ul, void const**>) + 18 1 Electron Framework 0x000000012add00e1 base::debug::StackTrace::StackTrace(unsigned long) + 225 2 Electron Framework 0x000000012ade978a base::allocator::UnretainedDanglingRawPtrDetectedCrash(unsigned long) + 90 3 Electron Framework 0x000000012ae437f7 base::internal::RawPtrBackupRefImpl<true>::ReportIfDanglingInternal(unsigned long) + 391 (cherry picked from commit f8d0412) --------- Co-authored-by: Charles Kerr <charles@charleskerr.com> Co-authored-by: Niklas Wenzel <dev@nikwen.de>

ckerr added semver/patch backwards-compatible bug fixes no-backport labels Apr 17, 2026

electron-cation Bot added the new-pr 🌱 PR opened recently label Apr 17, 2026

ckerr marked this pull request as draft April 17, 2026 15:18

nikwen reviewed Apr 17, 2026

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Comment thread shell/browser/api/electron_api_desktop_capturer.cc Outdated

nikwen reviewed Apr 17, 2026

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Comment thread shell/browser/api/electron_api_desktop_capturer.cc Outdated

fix: do not block indefinitely on thumbnails in desktopCapturer

b70aaf6

fixes dad4ab6 regression

ckerr force-pushed the fix/test-regression-f35122b-mediaDevice branch from 05b54bb to b70aaf6 Compare April 17, 2026 17:41

fix: build error

eb28833

nikwen reviewed Apr 17, 2026

View reviewed changes

Comment thread shell/browser/api/electron_api_desktop_capturer.cc Outdated

Comment thread shell/browser/api/electron_api_desktop_capturer.cc

fixup! fix: do not block indefinitely on thumbnails in desktopCapturer

fd13909

chore: remove unnecessary code

nikwen approved these changes Apr 17, 2026

View reviewed changes

Comment thread shell/browser/api/electron_api_desktop_capturer.cc Outdated

ckerr marked this pull request as ready for review April 17, 2026 21:46

Update shell/browser/api/electron_api_desktop_capturer.cc

5f63153

Co-authored-by: Niklas Wenzel <dev@nikwen.de>

electron-cation Bot removed the new-pr 🌱 PR opened recently label Apr 18, 2026

ckerr merged commit a1d28e6 into main Apr 19, 2026
69 checks passed

ckerr deleted the fix/test-regression-f35122b-mediaDevice branch April 19, 2026 18:48

nikwen mentioned this pull request Apr 19, 2026

feat: support heap profiling in contentTracing #50826

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jkleinsc mentioned this pull request May 5, 2026

fix: timing issue DCHECK crash in DesktopCapturer on macOS #51506

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fix: do not block indefinitely on thumbnails in desktopCapturer#51128

fix: do not block indefinitely on thumbnails in desktopCapturer#51128
ckerr merged 4 commits into
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