A customer reported that my app hangs at some point and he sent me a process analysis taken from Activity Monitor. To me it looks like two threads are calling URL.appendingPathComponent() at the same time and this causes a deadlock. Anyone knows how to avoid this and if this is a problem with macOS?
Call graph:
2662 Thread_13677 DispatchQueue_1: com.apple.main-thread (serial)
+ 2662 start (in libdyld.dylib) + 1 [0x7fff632ce7fd]
+ 2662 ??? (in myApp) load address 0x1086d0000 + 0x1bb9 [0x1086d1bb9]
+ 2662 NSApplicationMain (in AppKit) + 777 [0x7fff28dfc775]
+ 2662 -[NSApplication run] (in AppKit) + 658 [0x7fff28e2a3ae]
+ 2662 -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] (in AppKit) + 1352 [0x7fff28e38690]
+ 2662 _DPSNextEvent (in AppKit) + 990 [0x7fff28e39eb4]
+ 2662 _BlockUntilNextEventMatchingListInModeWithFilter (in HIToolbox) + 64 [0x7fff2a7c8127]
+ 2662 ReceiveNextEventCommon (in HIToolbox) + 600 [0x7fff2a7c839d]
+ 2662 RunCurrentEventLoopInMode (in HIToolbox) + 292 [0x7fff2a7c865d]
+ 2662 CFRunLoopRunSpecific (in CoreFoundation) + 499 [0x7fff2bc71bd3]
+ 2662 __CFRunLoopRun (in CoreFoundation) + 2370 [0x7fff2bc72b8a]
+ 2662 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ (in CoreFoundation) + 9 [0x7fff2bcb2e00]
+ 2662 _dispatch_main_queue_callback_4CF (in libdispatch.dylib) + 1105 [0x7fff63280bc4]
+ 2662 _dispatch_client_callout (in libdispatch.dylib) + 8 [0x7fff6327550e]
+ 2662 _dispatch_call_block_and_release (in libdispatch.dylib) + 12 [0x7fff63274583]
+ 2662 ??? (in myApp) load address 0x1086d0000 + 0xa3169 [0x108773169]
+ 2662 ??? (in myApp) load address 0x1086d0000 + 0x25f1e [0x1086f5f1e]
+ 2662 ??? (in myApp) load address 0x1086d0000 + 0x26201 [0x1086f6201]
+ 2662 ??? (in myApp) load address 0x1086d0000 + 0x87eb7 [0x108757eb7]
+ 2662 ??? (in myApp) load address 0x1086d0000 + 0x81da1 [0x108751da1]
+ 2662 ??? (in myApp) load address 0x1086d0000 + 0x6d18 [0x1086d6d18]
+ 2662 URL.appendingPathComponent(_:) (in libswiftFoundation.dylib) + 61 [0x7fff62e1e3ad]
+ 2662 -[NSURL(NSURLPathUtilities) URLByAppendingPathComponent:] (in Foundation) + 217 [0x7fff2e2e843a]
+ 2662 -[NSURL getResourceValue:forKey:error:] (in CoreFoundation) + 110 [0x7fff2bc5d4ff]
+ 2662 CFURLCopyResourcePropertyForKey (in CoreFoundation) + 119 [0x7fff2bc46958]
+ 2662 _FSURLCopyResourcePropertyForKeyInternal(__CFURL const*, __CFString const*, void*, void*, __CFError**, unsigned char) (in CoreServicesInternal) + 221 [0x7fff4472feba]
+ 2662 prepareValuesForBitmap(__CFURL const*, __FileCache*, _FilePropertyBitmap*, __CFError**) (in CoreServicesInternal) + 363 [0x7fff447337e4]
+ 2662 corePropertyProviderPrepareValues(__CFURL const*, __FileCache*, __CFString const* const*, void const**, long, void const*, __CFError**) (in CoreServicesInternal) + 631 [0x7fff44733ac4]
+ 2662 __getattrlist (in libsystem_kernel.dylib) + 10 [0x7fff6340fad2]
2662 Thread_13693 DispatchQueue_6: com.apple.root.background-qos (concurrent)
+ 2662 start_wqthread (in libsystem_pthread.dylib) + 15 [0x7fff634ce827]
+ 2662 _pthread_wqthread (in libsystem_pthread.dylib) + 220 [0x7fff634cf6b6]
+ 2662 _dispatch_worker_thread2 (in libdispatch.dylib) + 92 [0x7fff63283f22]
+ 2662 _dispatch_root_queue_drain (in libdispatch.dylib) + 663 [0x7fff63283933]
+ 2662 _dispatch_client_callout (in libdispatch.dylib) + 8 [0x7fff6327550e]
+ 2662 _dispatch_call_block_and_release (in libdispatch.dylib) + 12 [0x7fff63274583]
+ 2662 ??? (in myApp) load address 0x1086d0000 + 0xa3169 [0x108773169]
+ 2662 ??? (in myApp) load address 0x1086d0000 + 0x446aa [0x1087146aa]
+ 2662 ??? (in myApp) load address 0x1086d0000 + 0x46533 [0x108716533]
+ 2662 ??? (in myApp) load address 0x1086d0000 + 0x4a3d9 [0x10871a3d9]
+ 2662 ??? (in myApp) load address 0x1086d0000 + 0x4a3d9 [0x10871a3d9]
+ 2662 ??? (in myApp) load address 0x1086d0000 + 0x4a3d9 [0x10871a3d9]
+ 2662 ??? (in myApp) load address 0x1086d0000 + 0x4a3d9 [0x10871a3d9]
+ 2662 ??? (in myApp) load address 0x1086d0000 + 0x4a3d9 [0x10871a3d9]
+ 2662 ??? (in myApp) load address 0x1086d0000 + 0x4a3d9 [0x10871a3d9]
+ 2662 ??? (in myApp) load address 0x1086d0000 + 0x4a3be [0x10871a3be]
+ 2662 URL.appendingPathComponent(_:) (in libswiftFoundation.dylib) + 61 [0x7fff62e1e3ad]
+ 2662 -[NSURL(NSURLPathUtilities) URLByAppendingPathComponent:] (in Foundation) + 217 [0x7fff2e2e843a]
+ 2662 -[NSURL getResourceValue:forKey:error:] (in CoreFoundation) + 110 [0x7fff2bc5d4ff]
+ 2662 CFURLCopyResourcePropertyForKey (in CoreFoundation) + 119 [0x7fff2bc46958]
+ 2662 _FSURLCopyResourcePropertyForKeyInternal(__CFURL const*, __CFString const*, void*, void*, __CFError**, unsigned char) (in CoreServicesInternal) + 221 [0x7fff4472feba]
+ 2662 prepareValuesForBitmap(__CFURL const*, __FileCache*, _FilePropertyBitmap*, __CFError**) (in CoreServicesInternal) + 363 [0x7fff447337e4]
+ 2662 corePropertyProviderPrepareValues(__CFURL const*, __FileCache*, __CFString const* const*, void const**, long, void const*, __CFError**) (in CoreServicesInternal) + 631 [0x7fff44733ac4]
+ 2662 __getattrlist (in libsystem_kernel.dylib) + 10 [0x7fff6340fad2]
2662 Thread_13846: com.apple.NSEventThread
+ 2662 thread_start (in libsystem_pthread.dylib) + 15 [0x7fff634ce83b]
+ 2662 _pthread_start (in libsystem_pthread.dylib) + 148 [0x7fff634d2e65]
+ 2662 _NSEventThread (in AppKit) + 132 [0x7fff28fdca72]
+ 2662 CFRunLoopRunSpecific (in CoreFoundation) + 499 [0x7fff2bc71bd3]
+ 2662 __CFRunLoopRun (in CoreFoundation) + 1695 [0x7fff2bc728e7]
+ 2662 __CFRunLoopServiceMachPort (in CoreFoundation) + 322 [0x7fff2bc73d0b]
+ 2662 mach_msg (in libsystem_kernel.dylib) + 60 [0x7fff6340f5d0]
+ 2662 mach_msg_trap (in libsystem_kernel.dylib) + 10 [0x7fff6340f25a]
2662 Thread_59695 DispatchQueue_158: com.apple.CFVolumeObserver.0x600003dbf8a0 (serial)
+ 2662 start_wqthread (in libsystem_pthread.dylib) + 15 [0x7fff634ce827]
+ 2662 _pthread_wqthread (in libsystem_pthread.dylib) + 290 [0x7fff634cf6fc]
+ 2662 _dispatch_workloop_worker_thread (in libdispatch.dylib) + 598 [0x7fff63284a9e]
+ 2662 _dispatch_lane_invoke (in libdispatch.dylib) + 363 [0x7fff6327b452]
+ 2662 _dispatch_lane_serial_drain (in libdispatch.dylib) + 263 [0x7fff6327a980]
+ 2662 _dispatch_source_invoke (in libdispatch.dylib) + 2084 [0x7fff632873c4]
+ 2662 _dispatch_continuation_pop (in libdispatch.dylib) + 414 [0x7fff632776c0]
+ 2662 _dispatch_client_callout (in libdispatch.dylib) + 8 [0x7fff6327550e]
+ 2662 __DASessionSetDispatchQueue_block_invoke_2 (in DiskArbitration) + 56 [0x7fff2df7de66]
+ 2662 _DASessionCallback (in DiskArbitration) + 259 [0x7fff2df7df70]
+ 2662 _DADispatchCallback (in DiskArbitration) + 198 [0x7fff2df7e254]
+ 2662 _VolumeObserverDiskUnmountApprovalCallback (in CoreFoundation) + 159 [0x7fff2bd5d738]
+ 2662 __createVolumeObserverSubsystem_block_invoke (in AppKit) + 992 [0x7fff291110ea]
+ 2662 _dispatch_semaphore_wait_slow (in libdispatch.dylib) + 98 [0x7fff63275e6a]
+ 2662 _dispatch_sema4_wait (in libdispatch.dylib) + 16 [0x7fff6327599d]
+ 2662 semaphore_wait_trap (in libsystem_kernel.dylib) + 10 [0x7fff6340f296]
2662 Thread_233483
2662 start_wqthread (in libsystem_pthread.dylib) + 15 [0x7fff634ce827]
2662 _pthread_wqthread (in libsystem_pthread.dylib) + 390 [0x7fff634cf760]
2662 __workq_kernreturn (in libsystem_kernel.dylib) + 10 [0x7fff6341092e]
