UI API called on a background thread com.google.Maps.LabelingBehavior

Question

After upgrading to XCode 9 I suddently get the following warning when I run my app:

Main Thread Checker: UI API called on a background thread: -[UIApplication applicationState]
PID: 15473, TID: 773864, Thread name: com.google.Maps.LabelingBehavior, Queue name: com.apple.root.default-qos.overcommit, QoS: 21
Backtrace:
4   App                          0x000000010b8ee524 GMSIsApplicationInBackground + 53
5   App                          0x000000010b8dc77a -[GMSForegroundDispatchQueue initWithName:targetQueue:] + 269
6   App                          0x000000010b9bc5ee _ZN7gmscore6vector4text8GlyphSetC2ERKNS_4base10reffed_ptrINS0_16TextureAtlasPoolEEEPU28objcproto17OS_dispatch_queue8NSObjectPK8__CTFontff + 344
7   App                          0x000000010b9bba58 _ZN7gmscore6vector4text10GlyphCache11GetGlyphSetEPK8__CTFontf + 214
8   App                          0x000000010b9b950e _ZN7gmscore6vector4text6GLText14PrefetchGlyphsERKNS_4base10reffed_ptrINS1_10GlyphCacheEEERKNSt3__16vectorItNS9_9allocatorItEEEEPK8__CTFontf + 22
9   App                          0x000000010b9b9611 _ZN7gmscore6vector4text6GLText14PrefetchGlyphsERKNS_4base10reffed_ptrINS1_10GlyphCacheEEEPK8__CTLinebf + 207
10  App                          0x000000010b9112df _ZN7gmscore6vector12GLPointLabel22PrefetchGlyphsForGroupEPNS0_12GLLabelGroupE + 181
11  App                          0x000000010b911207 _ZN7gmscore6vector12GLPointLabel14PrefetchGlyphsEv + 33
12  App                          0x000000010b98022a _ZN7gmscore6vector16LabelingBehavior23CreatePendingOperationsERKNSt3__13setINS_4base10reffed_ptrINS0_7GLLabelEEENS2_4lessIS7_EENS2_9allocatorIS7_EEEESE_SE_NS0_13LabelDrawModeE + 1096
13  App                          0x000000010b97fb9d _ZN7gmscore6vector16LabelingBehavior14RunLabelingJobERKNS_4base10reffed_ptrINS1_11LabelingJobEEE + 357
14  App                          0x000000010b97fa2a ___ZN7gmscore6vector16LabelingBehavior14CommitInternalEPNS_8renderer14EntityRendererE_block_invoke + 22
15  Foundation                          0x0000000110bb0948 __NSThreadPerformPerform + 334
16  CoreFoundation                      0x00000001117af2b1 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
17  CoreFoundation                      0x000000011184ed31 __CFRunLoopDoSource0 + 81
18  CoreFoundation                      0x0000000111793c19 __CFRunLoopDoSources0 + 185
19  CoreFoundation                      0x00000001117931ff __CFRunLoopRun + 1279
20  CoreFoundation                      0x0000000111792a89 CFRunLoopRunSpecific + 409
21  Foundation                          0x0000000110b6ae5e -[NSRunLoop(NSRunLoop) runMode:beforeDate:] + 274
22  App                                 0x000000010b9bace5 -[GMSx_GTMSimpleWorkerThread main] + 337
23  Foundation                          0x0000000110b788ac __NSThread__start__ + 1197
24  libsystem_pthread.dylib             0x000000011323393b _pthread_body + 180
25  libsystem_pthread.dylib             0x0000000113233887 _pthread_body + 0
26  libsystem_pthread.dylib             0x000000011323308d thread_start + 13
Error Domain=kCLErrorDomain Code=0 "(null)"

I can narrow it down to the problem happens when I assign the map to my view.

override func viewDidLoad() {
    super.viewDidLoad()
    UIApplication.shared.isIdleTimerDisabled = true
    GPSManager.instance.startGPS()
    setupLayout()


    map = GMSMapView.map(withFrame: CGRect.zero, camera: getCamera(location: initialLocation, zoom: 10))
    map.mapType = .hybrid
    map.delegate = self
    map.settings.consumesGesturesInView = false

    self.view.addSubview(map) <-- This is where is goes wrong
    self.view.sendSubview(toBack: map)

    configureMenus()
}

Is this something I can fix or is it inside Google Maps? Cheers

Answer 1

The problem is inside the Google library.

If you don't want this kind of warning you can disable Main Thread Checker inside the Scheme options.

Go Product > Scheme > Manage Schemes search the Scheme you use for your tests and press Edit... in the left sidebar press Run and then go to Diagnostics and uncheck Main Thread Checker checkbox.

This is only a temporal solution if you don't want these warnings. I do not recommend it because you could introduce bugs if call UI inside a background thread

If you have test you should disable the checkbox in Test option as I explained in Xcode 9, iOS 11, XCUITest failure: Main Thread Checker Flurry Analytics if you do not want the tests crash