# UI API called on a background thread when I start screen sharing **URL:** \ **Category:** macOS\ **Created:** [November 22, 2021, 7:50am UTC](https://devforum.zoom.us/t/ui-api-called-on-a-background-thread-when-i-start-screen-sharing/60531 "2021-11-22T07:50:48Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![anton.yereshchenko](https://sea2.discourse-cdn.com/flex016/user_avatar/devforum.zoom.us/anton.yereshchenko/32/16916_2.png) [@anton.yereshchenko](https://devforum.zoom.us/u/anton.yereshchenko)\ **Post date:** [November 22, 2021, 7:50am UTC](https://devforum.zoom.us/t/ui-api-called-on-a-background-thread-when-i-start-screen-sharing/60531/1 "2021-11-22T07:50:49Z")
Hi, I have noticed some info logs while call those methods (_but only for first call_): `- (ZoomSDKError)startMonitorShare:(CGDirectDisplayID)monitorID` `- (ZoomSDKError)startAppShare:(CGWindowID)windowID` The logs say us that some UI stuff (`[NSWindow windowNumber]` and `[NSApplication windows]`) isn’t use in the main thread. **Logs example:** ```auto ================================================================= Main Thread Checker: UI API called on a background thread: -[NSWindow windowNumber] PID: 1265, TID: 33933, Thread name: capture thread, Queue name: com.apple.root.default-qos.overcommit, QoS: 0 Backtrace: 4 nydus 0x00000001416b3c32 nydus + 183346 5 nydus 0x00000001416a0c93 nydus + 105619 6 nydus 0x00000001416a0fd7 nydus + 106455 7 nydus 0x0000000141698bdc nydus + 72668 8 nydus 0x000000014169e835 nydus + 96309 9 nydus 0x000000014169e5a3 nydus + 95651 10 CoreFoundation 0x00007fff20606e24 __CFMessagePortPerform + 779 11 CoreFoundation 0x00007fff205620d4 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 41 12 CoreFoundation 0x00007fff20561fb5 __CFRunLoopDoSource1 + 619 13 CoreFoundation 0x00007fff2056063f __CFRunLoopRun + 2400 14 CoreFoundation 0x00007fff2055f61c CFRunLoopRunSpecific + 563 15 nydus 0x000000014169dede nydus + 93918 16 nydus 0x0000000141692d3d nydus + 48445 17 libsystem_pthread.dylib 0x00000001106271b8 _pthread_start + 224 18 libsystem_pthread.dylib 0x0000000110622af7 thread_start + 15 2021-11-18 19:37:00.069282+0200 PROJECT Dev[1265:33933] [reports] Main Thread Checker: UI API called on a background thread: -[NSWindow windowNumber] PID: 1265, TID: 33933, Thread name: capture thread, Queue name: com.apple.root.default-qos.overcommit, QoS: 0 Backtrace: 4 nydus 0x00000001416b3c32 nydus + 183346 5 nydus 0x00000001416a0c93 nydus + 105619 6 nydus 0x00000001416a0fd7 nydus + 106455 7 nydus 0x0000000141698bdc nydus + 72668 8 nydus 0x000000014169e835 nydus + 96309 9 nydus 0x000000014169e5a3 nydus + 95651 10 CoreFoundation 0x00007fff20606e24 __CFMessagePortPerform + 779 11 CoreFoundation 0x00007fff205620d4 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 41 12 CoreFoundation 0x00007fff20561fb5 __CFRunLoopDoSource1 + 619 13 CoreFoundation 0x00007fff2056063f __CFRunLoopRun + 2400 14 CoreFoundation 0x00007fff2055f61c CFRunLoopRunSpecific + 563 15 nydus 0x000000014169dede nydus + 93918 16 nydus 0x0000000141692d3d nydus + 48445 17 libsystem_pthread.dylib 0x00000001106271b8 _pthread_start + 224 18 libsystem_pthread.dylib 0x0000000110622af7 thread_start + 15 ================================================================= Main Thread Checker: UI API called on a background thread: -[NSApplication windows] PID: 1265, TID: 33933, Thread name: capture thread, Queue name: com.apple.root.default-qos.overcommit, QoS: 0 Backtrace: 4 nydus 0x00000001416c0d13 nydus + 236819 5 nydus 0x00000001416bb3c3 nydus + 213955 6 nydus 0x00000001416a7d75 nydus + 134517 7 nydus 0x000000014169a73a nydus + 79674 8 nydus 0x000000014169bfa0 nydus + 85920 9 nydus 0x000000014169e9de nydus + 96734 10 nydus 0x000000014169def3 nydus + 93939 11 nydus 0x0000000141692d3d nydus + 48445 12 libsystem_pthread.dylib 0x00000001106271b8 _pthread_start + 224 13 libsystem_pthread.dylib 0x0000000110622af7 thread_start + 15 2021-11-18 19:37:00.510993+0200 PROJECT Dev[1265:33933] [reports] Main Thread Checker: UI API called on a background thread: -[NSApplication windows] PID: 1265, TID: 33933, Thread name: capture thread, Queue name: com.apple.root.default-qos.overcommit, QoS: 0 Backtrace: 4 nydus 0x00000001416c0d13 nydus + 236819 5 nydus 0x00000001416bb3c3 nydus + 213955 6 nydus 0x00000001416a7d75 nydus + 134517 7 nydus 0x000000014169a73a nydus + 79674 8 nydus 0x000000014169bfa0 nydus + 85920 9 nydus 0x000000014169e9de nydus + 96734 10 nydus 0x000000014169def3 nydus + 93939 11 nydus 0x0000000141692d3d nydus + 48445 12 libsystem_pthread.dylib 0x00000001106271b8 _pthread_start + 224 13 libsystem_pthread.dylib 0x0000000110622af7 thread_start + 15 ``` ---
**Author:** ![jon.zoom](https://sea2.discourse-cdn.com/flex016/user_avatar/devforum.zoom.us/jon.zoom/32/13495_2.png) [@jon.zoom](https://devforum.zoom.us/u/jon.zoom)\ **Post date:** [November 22, 2021, 10:28pm UTC](https://devforum.zoom.us/t/ui-api-called-on-a-background-thread-when-i-start-screen-sharing/60531/2 "2021-11-22T22:28:06Z")
Hi @anton.yereshchenko, thanks for bringing this to our attention. We’ll investigate this and let you know as soon as we have any updates. Thanks! ---
**Author:** ![system](https://us1.discourse-cdn.com/flex016/uploads/zoomdeveloper/original/3X/6/1/614bdd549b610bbaa46ff934617683a02bdaa03c.png) [@system](https://devforum.zoom.us/u/system)\ **Post date:** [December 23, 2021, 8:28am UTC](https://devforum.zoom.us/t/ui-api-called-on-a-background-thread-when-i-start-screen-sharing/60531/3 "2021-12-23T08:28:30Z")
Closed on December 23, 2021, 8:28am UTC This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.