Thread waiting on a lower QoS thread

[data-sync-user]

Thread Performance Checker: Thread running at QOS_CLASS_USER_INTERACTIVE waiting on a lower QoS thread running at QOS_CLASS_DEFAULT. Investigate ways to avoid priority inversions
PID: 38362, TID: 209725
Backtrace
=================================================================
4   Shared                              0x000000010c645434 $s6Shared8DeferredC5valuexvg + 660
5   Sync                                0x000000010b93948f $s7Storage10RustPlacesC24migrateBookmarksIfNeeded13fromBrowserDByAA0iJ0C_tF + 703
6   Client                              0x00000001081e55ac $s6Client14BrowserProfileC6reopenyyF + 460
7   Client                              0x000000010820a5f1 $s6Client14BrowserProfileCAA0C0A2aDP6reopenyyFTW + 17
8   Client                              0x0000000108055352 $s6Client11AppDelegateC26applicationDidBecomeActiveyySo13UIApplicationCF + 450
9   Client                              0x0000000108056c74 $s6Client11AppDelegateC19handleNotificationsyy10Foundation12NotificationVF + 436
10  Client                              0x0000000108056f1f $s6Client11AppDelegateC19handleNotificationsyy10Foundation12NotificationVFTo + 111
11  CoreFoundation                      0x00007ff80035869b __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 137
12  CoreFoundation                      0x00007ff8003585d1 ___CFXRegistrationPost_block_invoke + 86
13  CoreFoundation                      0x00007ff800357bb0 _CFXRegistrationPost + 541
14  CoreFoundation                      0x00007ff8003574b9 _CFXNotificationPost + 822
15  Foundation                          0x00007ff800c08501 -[NSNotificationCenter postNotificationName:object:userInfo:] + 82
16  UIKitCore                           0x000000010f5bcfba -[UIApplication _stopDeactivatingForReason:] + 1472
17  UIKitCore                           0x000000010e9f9620 -[_UISceneLifecycleMultiplexer _performBlock:withApplicationOfDeactivationReasons:fromReasons:] + 333
18  UIKitCore                           0x000000010e9f99c8 -[_UISceneLifecycleMultiplexer _evalTransitionToSettings:fromSettings:forceExit:withTransitionStore:] + 831
19  UIKitCore                           0x000000010e9f9275 -[_UISceneLifecycleMultiplexer uiScene:transitionedFromState:withTransitionContext:] + 354
20  UIKitCore                           0x000000010ea080e1 __186-[_UIWindowSceneFBSSceneTransitionContextDrivenLifecycleSettingsDiffAction _performActionsForUIScene:withUpdatedFBSScene:settingsDiff:fromSettings:transitionContext:lifecycleActionType:]_block_invoke + 178
21  UIKitCore                           0x000000010ef3c363 +[BSAnimationSettings(UIKit) tryAnimatingWithSettings:fromCurrentState:actions:completion:] + 833
22  UIKitCore                           0x000000010f08942f _UISceneSettingsDiffActionPerformChangesWithTransitionContextAndCompletion + 257
23  UIKitCore                           0x000000010ea07d61 -[_UIWindowSceneFBSSceneTransitionContextDrivenLifecycleSettingsDiffAction _performActionsForUIScene:withUpdatedFBSScene:settingsDiff:fromSettings:transitionContext:lifecycleActionType:] + 348
24  UIKitCore                           0x000000010e7eaf16 __64-[UIScene scene:didUpdateWithDiff:transitionContext:completion:]_block_invoke.594 + 815
25  UIKitCore                           0x000000010e7e992c -[UIScene _emitSceneSettingsUpdateResponseForCompletion:afterSceneUpdateWork:] + 245
26  UIKitCore                           0x000000010e7eaac3 -[UIScene scene:didUpdateWithDiff:transitionContext:completion:] + 255
27  UIKitCore                           0x000000010ef6f0c6 -[UIApplicationSceneClientAgent scene:handleEvent:withCompletion:] + 475
28  FrontBoardServices                  0x00007ff80547cd94 -[FBSScene updater:didUpdateSettings:withDiff:transitionContext:completion:] + 521
29  FrontBoardServices                  0x00007ff8054ac45a __94-[FBSWorkspaceScenesClient _queue_updateScene:withSettings:diff:transitionContext:completion:]_block_invoke_2 + 133
30  FrontBoardServices                  0x00007ff80548a46a -[FBSWorkspace _calloutQueue_executeCalloutFromSource:withBlock:] + 209
31  FrontBoardServices                  0x00007ff8054ac3a2 __94-[FBSWorkspaceScenesClient _queue_updateScene:withSettings:diff:transitionContext:completion:]_block_invoke + 372
32  libdispatch.dylib                   0x000000010aaebf5b _dispatch_client_callout + 8
33  libdispatch.dylib                   0x000000010aaef8d2 _dispatch_block_invoke_direct + 496
34  FrontBoardServices                  0x00007ff8054d0980 __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__ + 30
35  FrontBoardServices                  0x00007ff8054d0876 -[FBSSerialQueue _targetQueue_performNextIfPossible] + 174
36  FrontBoardServices                  0x00007ff8054d09a8 -[FBSSerialQueue _performNextFromRunLoopSource] + 19
37  CoreFoundation                      0x00007ff800387035 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
38  CoreFoundation                      0x00007ff800386f74 __CFRunLoopDoSource0 + 157
39  CoreFoundation                      0x00007ff800386771 __CFRunLoopDoSources0 + 212
40  CoreFoundation                      0x00007ff800380e73 __CFRunLoopRun + 927
41  CoreFoundation                      0x00007ff8003806f7 CFRunLoopRunSpecific + 560
42  GraphicsServices                    0x00007ff809c5c28a GSEventRunModal + 139
43  UIKitCore                           0x000000010f5c262b -[UIApplication _run] + 994
44  UIKitCore                           0x000000010f5c7547 UIApplicationMain + 123
45  Client                              0x0000000108331602 main + 930

!Screen Shot 2022-11-28 at 11.38.34 AM.png|width=1948,height=406!

┆Issue is synchronized with this Jira Task

[data-sync-user]

➤ Laurie Marceau commented:

Happened with this stacktrace too

hread Performance Checker: Thread running at QOS_CLASS_USER_INTERACTIVE waiting on a lower QoS thread running at QOS_CLASS_DEFAULT. Investigate ways to avoid priority inversions
PID: 95025, TID: 7203141
Backtrace

3 Client 0x00000001051b37b4 -[GCDWebServer stop] + 392
4 Client 0x00000001051b3e54 -[GCDWebServer stop] + 224
5 Client 0x0000000104d20328 $s6Client11AppDelegateC29applicationDidEnterBackgroundyySo13UIApplicationCFyycfU + 112
6 Client 0x0000000104905054 $sIeg_IeyB_TR + 48
7 libdispatch.dylib 0x000000010763e05c _dispatch_client_callout + 20
8 libdispatch.dylib 0x00000001076411e8 _dispatch_continuation_pop + 792
9 libdispatch.dylib 0x0000000107657ed0 _dispatch_source_invoke + 1668
10 libdispatch.dylib 0x000000010764e670 _dispatch_main_queue_drain + 780
11 libdispatch.dylib 0x000000010764e354 _dispatch_main_queue_callback_4CF + 44
12 CoreFoundation 0x000000018f4066f8 5CDC5D9A-E506-3740-B64E-BB30867B4F1B + 632568
13 CoreFoundation 0x000000018f3e8058 5CDC5D9A-E506-3740-B64E-BB30867B4F1B + 507992
14 CoreFoundation 0x000000018f3eced4 CFRunLoopRunSpecific + 612
15 GraphicsServices 0x00000001c86ee368 GSEventRunModal + 164
16 UIKitCore 0x00000001918cb3d0 179501B6-0FC2-344A-B969-B4E3961EBE10 + 3810256
17 UIKitCore 0x00000001918cb034 UIApplicationMain + 340
18 Client 0x0000000104fe4d90 main + 864
19 dyld 0x00000001ada54960 CB3FF411-4762-34D2-86A4-ECA13F9FB6C3 + 88416

[tarikeshaq]

5 Sync 0x000000010b93948f $s7Storage10RustPlacesC24migrateBookmarksIfNeeded13fromBrowserDByAA0iJ0C_tF + 703

We can safely remove the old migrateBookmarksIfNeededFromBrowserDB. it's very old and I have reason to believe it was very broken anyways. Looks like it was removed in the past, but was restored in https://github.com/mozilla-mobile/firefox-ios/pull/6393/files because it broke tests. I'll try a PR removing it to see if tests fail. Otherwise we should probably mark it so it only runs in tests.

[data-sync-user]

➤ Orla Mitchell commented:

For QA please verify there are no new visible performance regressions, such as slow downs or hangs during regular use.

[data-sync-user]

➤ Andrei Bodea commented:

Verified as fixed on v117 (33169) with iPhone 13 Pro (15.7.1).