[Impeller] acquire the gpu sync switch when flush stored GPU tasks. #169596

jonahwilliams · 2025-05-28T16:18:22Z

Potential fix for #166668

See:

https://github.com/flutter/flutter/blob/master/engine/src/flutter/impeller/renderer/backend/metal/context_mtl.mm#L429
flutter/engine/src/flutter/fml/synchronization/sync_switch.cc

Line 41 in 5d013c7

observer->OnSyncSwitchUpdate(value);

We don't hold the sync switch lock when we flush tasks. So if we start flushing then immediately go to the background, then we might execute while backgrounded.

gaaclarke

This approach is looking good to me.

gaaclarke · 2025-05-28T16:40:57Z

engine/src/flutter/impeller/renderer/backend/metal/context_mtl.mm

+            for (const auto& task : tasks_awaiting_gpu) {
+              task.task();
+            }


Do you think we should acquire the lock inside the loop? My concern is that if this takes too much time the OS might kill the process.

hmm, yeah that is a good point.

gaaclarke

lgtm!

…U tasks. (flutter/flutter#169596)

zanderso · 2025-06-12T19:54:45Z

@jonahwilliams The internal customer is reporting that after this change, the images still briefly show up as pink before loading in correctly. Does that sound plausible?

jonahwilliams · 2025-06-12T21:10:57Z

We can do #169378 too.

the images still briefly show up as pink before loading in correctly. Does that sound plausible?

There is no automated retry built into this system, likely they have some business logic that is refreshing the images which covers up the images that were incorrectly decoded.

…lutter#169596) Potential fix for flutter#166668 See: * https://github.com/flutter/flutter/blob/master/engine/src/flutter/impeller/renderer/backend/metal/context_mtl.mm#L429 * https://github.com/flutter/flutter/blob/5d013c73baa70a8b3e1c541cb63e4c22654aa3cc/engine/src/flutter/fml/synchronization/sync_switch.cc#L41 We don't hold the sync switch lock when we flush tasks. So if we start flushing then immediately go to the background, then we might execute while backgrounded.

Includes: * #169596 * #169378 Fix image decode errors on iOS that could occur if a push notification triggered image decoding while the app is backgrounded.

Includes: * flutter/flutter#169596 * flutter/flutter#169378 Fix image decode errors on iOS that could occur if a push notification triggered image decoding while the app is backgrounded.

…U tasks. (flutter/flutter#169596)

jonahwilliams added 2 commits May 28, 2025 09:01

[Impeller] hold sync switch while flushing tasks.

1c90f84

add testing.

529ecd9

jonahwilliams requested a review from gaaclarke May 28, 2025 16:18

github-actions bot added engine flutter/engine related. See also e: labels. e: impeller Impeller rendering backend issues and features requests labels May 28, 2025

gaaclarke reviewed May 28, 2025

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jonahwilliams added 2 commits May 28, 2025 10:05

flush per task.

ce948ba

++

5a1483c

gaaclarke approved these changes May 28, 2025

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Merged via the queue into flutter:master with commit af3627a May 29, 2025
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jonahwilliams mentioned this pull request Jun 18, 2025

[CP] Fix pink images when returning from background on iOS #170846

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[Impeller] acquire the gpu sync switch when flush stored GPU tasks. #169596

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