Diagnosing run loop issue (partially frozen UI) in Cocoa application - objective-c

Question

Our application has a fairly standard layout - a main window with a toolbar, source list on the left hand side, and a tab control. The contents of the tabs is drawn by a third party component that is open source and very complex. It makes extensive use of threads, etc.
Some users can reliably reproduce a situation where the whole application 'freezes' - which is to say, the main window stops redrawing. The cursor does not beachball, and the user can still click around, but the window simply does not update.
There is no specific repro steps other than starting to use the application, open one or more tabs and within a few minutes the problem occurs.
They are able to open the application menus at the top of the screen. One of the menu items - "Check for updates" - starts a modal session (a sheet with a progress indicator) while checking for updates on a background thread.
When the application is in this 'frozen' state, choosing 'Check for updates' seems to unfreeze the application for the duration of the modal session. Clicks and button presses that were made while frozen are suddenly registered as the UI redraws.
Then, the 'Check for updates' finishes, the modal session ends and the application is frozen again.
It seems to me to be a problem with the run loop. It's an open-ended question but I honestly don't know where to look - what can cause these kind of symptoms? I am unable to see any correlation between the hardware/software of the users that experience this issue.
EDIT
After freezing, the only thing I see on the console that I can't explain is
12/18/2013 10:39:29.000 AM kernel[0]: Network delay is not specified! Defaulting to 0x384
But I think this is a red herring.
A sample of the process when it's frozen shows this for the UI thread:
+ 2327 -[NSApplication run] (in AppKit) + 727 [0x9392e35c]
+ 2327 -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] (in AppKit) + 119 [0x9393bad0]
+ 2327 _DPSNextEvent (in AppKit) + 1602 [0x9393c5a9]
+ 2327 _BlockUntilNextEventMatchingListInModeWithFilter (in HIToolbox) + 92 [0x9b2ea98d]
+ 2327 ReceiveNextEventCommon (in HIToolbox) + 526 [0x9b2eabb2]
+ 2327 RunCurrentEventLoopInMode (in HIToolbox) + 259 [0x9b2eae2d]
+ 2327 CFRunLoopRunInMode (in CoreFoundation) + 123 [0x95467bbb]
+ 2327 CFRunLoopRunSpecific (in CoreFoundation) + 394 [0x95467d5a]
+ 2324 __CFRunLoopRun (in CoreFoundation) + 1393 [0x95468541]
+ ! 2324 __CFRunLoopServiceMachPort (in CoreFoundation) + 169 [0x95468f69]
+ ! 2324 mach_msg (in libsystem_kernel.dylib) + 68 [0x99c0616c]
+ ! 2324 mach_msg_trap (in libsystem_kernel.dylib) + 10 [0x99c06f7a]
+ 3 __CFRunLoopRun (in CoreFoundation) + 1779 [0x954686c3]
+ 1 __CFRunLoopDoTimers (in CoreFoundation) + 222 [0x9552b22e]
+ : 1 CFArrayCreateMutable (in CoreFoundation) + 138 [0x9540a02a]
+ : 1 -[__NSPlaceholderArray initWithCapacity:] (in CoreFoundation) + 136 [0x954005a8]
+ : 1 +[__NSArrayM __new:::::] (in CoreFoundation) + 798 [0x9540096e]
+ 1 __CFRunLoopDoTimers (in CoreFoundation) + 237 [0x9552b23d]
+ : 1 CFArrayAppendValue (in CoreFoundation) + 157 [0x9541fa9d]
+ : 1 -[__NSArrayM addObject:] (in CoreFoundation) + 64 [0x954009e0]
+ : 1 -[__NSArrayM insertObject:atIndex:] (in CoreFoundation) + 400 [0x95400b90]
+ : 1 _platform_bzero$VARIANT$sse42 (in libsystem_platform.dylib) + 51 [0x9660c233]
+ 1 __CFRunLoopDoTimers (in CoreFoundation) + 349 [0x9552b2ad]
+ 1 __CFRunLoopDoTimer (in CoreFoundation) + 1395 [0x954b0b43]
+ 1 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ (in CoreFoundation) + 22 [0x954b1186]
+ 1 WebCore::timerFired(__CFRunLoopTimer*, void*) (in WebCore) + 64 [0x9285bff0]
+ 1 WebCore::ThreadTimers::sharedTimerFired() (in WebCore) + 84 [0x9285c064]
+ 1 WebCore::ThreadTimers::sharedTimerFiredInternal() (in WebCore) + 330 [0x9285c1ca]
+ 1 WebCore::MainThreadSharedTimer::setFireInterval(double) (in WebCore) + 21 [0x9285ba65]
+ 1 WebCore::setSharedTimerFireInterval(double) (in WebCore) + 173 [0x9285bb1d]
+ 1 CFRunLoopAddTimer (in CoreFoundation) + 453 [0x9546fed5]
+ 1 CFSetApplyFunction (in CoreFoundation) + 147 [0x954554d3]
+ 1 CFBasicHashApply (in CoreFoundation) + 122 [0x95437b4a]
+ 1 __CFSetApplyFunction_block_invoke (in CoreFoundation) + 25 [0x95455519]
+ 1 __CFRunLoopAddItemToCommonModes (in CoreFoundation) + 60 [0x9545556c]
But I am not able to interpret that information...
EDIT 2
An additional sample; clearly different to the first:
+ 2352 -[NSApplication run] (in AppKit) + 727 [0x9887035c]
+ 2352 -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] (in AppKit) + 119 [0x9887dad0]
+ 2352 _DPSNextEvent (in AppKit) + 1602 [0x9887e5a9]
+ 2352 _BlockUntilNextEventMatchingListInModeWithFilter (in HIToolbox) + 92 [0x9428298d]
+ 2352 ReceiveNextEventCommon (in HIToolbox) + 526 [0x94282bb2]
+ 2352 RunCurrentEventLoopInMode (in HIToolbox) + 259 [0x94282e2d]
+ 2352 CFRunLoopRunInMode (in CoreFoundation) + 123 [0x930d6bbb]
+ 2352 CFRunLoopRunSpecific (in CoreFoundation) + 394 [0x930d6d5a]
+ 2332 __CFRunLoopRun (in CoreFoundation) + 1393 [0x930d7541]
+ ! 2332 __CFRunLoopServiceMachPort (in CoreFoundation) + 169 [0x930d7f69]
+ ! 2332 mach_msg (in libsystem_kernel.dylib) + 68 [0x91bc316c]
+ ! 2332 mach_msg_trap (in libsystem_kernel.dylib) + 10 [0x91bc3f7a]
+ 17 __CFRunLoopRun (in CoreFoundation) + 1779 [0x930d76c3]
+ ! 16 __CFRunLoopDoTimers (in CoreFoundation) + 349 [0x9319a2ad]
+ ! : 10 __CFRunLoopDoTimer (in CoreFoundation) + 1395 [0x9311fb43]
+ ! : | 10 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ (in CoreFoundation) + 22 [0x93120186]
+ ! : | 4 __NSFireTimer (in Foundation) + 117 [0x96cac78b]
+ ! : | + 4 -[ThirdPartyView nsTimerCallBack:] (in ThirdPartyLib) + 61 [0x24958bd]
+ ! : | + 1 -[NSPasteboard changeCount] (in AppKit) + 19 [0x98a44fc6]
+ ! : | + ! 1 CFPasteboardGetGenerationCount (in CoreFoundation) + 0 [0x930e3470]
+ ! : | + 1 -[NSPasteboard changeCount] (in AppKit) + 0 [0x98a44fb3]
+ ! : | + 1 DYLD-STUB$$CFPasteboardGetGenerationCount (in AppKit) + 0 [0x992f994c]
+ ! : | + 1 objc_msgSend (in libobjc.A.dylib) + 26 [0x9b1094aa]
+ ! : | 3 __NSFireTimer (in Foundation) + 164 [0x96cac7ba]
+ ! : | + 3 _CFAutoreleasePoolPop (in CoreFoundation) + 47 [0x9309bcdf]
+ ! : | + 3 (anonymous namespace)::AutoreleasePoolPage::pop(void*) (in libobjc.A.dylib) + 559 [0x9b10b4b7]
+ ! : | 2 __NSFireTimer (in Foundation) + 98 [0x96cac778]
+ ! : | + 2 ??? (in <unknown binary>) [0x3589ca0]
+ ! : | + 2 ??? (in <unknown binary>) [0x99575bc]
+ ! : | + 2 ??? (in <unknown binary>) [0x9957668]
+ ! : | + 1 _objc_rootRetainCount (in libobjc.A.dylib) + 88 [0x9b10bdd0]
+ ! : | + ! 1 objc::DenseMapBase<objc::DenseMap<objc_object*, unsigned long, true, objc::DenseMapInfo<objc_object*> >, objc_object*, unsigned long, objc::DenseMapInfo<objc_object*>, true>::find(objc_object* const&) (in libobjc.A.dylib) + 32 [0x9b11f820]
+ ! : | + ! 1 bool objc::DenseMapBase<objc::DenseMap<objc_object*, unsigned long, true, objc::DenseMapInfo<objc_object*> >, objc_object*, unsigned long, objc::DenseMapInfo<objc_object*>, true>::LookupBucketFor<objc_object*>(objc_object* const&, std::__1::pair<objc_object*, unsigned long> const*&) const (in libobjc.A.dylib) + 73 [0x9b11f9ff]
+ ! : | + 1 objc_msgSend (in libobjc.A.dylib) + 64 [0x9b1094d0]
+ ! : | 1 __NSFireTimer (in Foundation) + 53 [0x96cac74b]
+ ! : | 1 NSPushAutoreleasePool (in Foundation) + 0 [0x96c4a188]
+ ! : 4 __CFRunLoopDoTimer (in CoreFoundation) + 557 [0x9311f7fd]
+ ! : | 3 __CFArmNextTimerInMode (in CoreFoundation) + 773 [0x930df535]
+ ! : | + 3 mk_timer_arm (in libsystem_kernel.dylib) + 10 [0x91bc40ca]
+ ! : | 1 __CFArmNextTimerInMode (in CoreFoundation) + 554 [0x930df45a]
+ ! : | 1 __CFTSRToNanoseconds (in CoreFoundation) + 25 [0x931bedb9]
+ ! : 1 __CFRunLoopDoTimer (in CoreFoundation) + 1556 [0x9311fbe4]
+ ! : | 1 pthread_mutex_lock (in libsystem_pthread.dylib) + 16 [0x911ca7ac]
+ ! : | 1 _pthread_mutex_lock (in libsystem_pthread.dylib) + 181 [0x911ca866]
+ ! : 1 __CFRunLoopDoTimer (in CoreFoundation) + 2093 [0x9311fdfd]
+ ! : 1 __CFRunLoopFindMode (in CoreFoundation) + 174 [0x930b1b5e]
+ ! : 1 _CFRuntimeSetInstanceTypeIDAndIsa (in CoreFoundation) + 33 [0x93065711]
+ ! : 1 _CFRuntimeSetInstanceTypeID (in CoreFoundation) + 0 [0x93063f50]
+ ! 1 __CFRunLoopDoTimers (in CoreFoundation) + 237 [0x9319a23d]
+ ! 1 CFArrayAppendValue (in CoreFoundation) + 157 [0x9308ea9d]
+ ! 1 -[__NSArrayM addObject:] (in CoreFoundation) + 64 [0x9306f9e0]
+ ! 1 -[__NSArrayM insertObject:atIndex:] (in CoreFoundation) + 400 [0x9306fb90]
+ ! 1 _platform_bzero$VARIANT$sse42 (in libsystem_platform.dylib) + 0 [0x94d2d200]
+ 2 __CFRunLoopRun (in CoreFoundation) + 1601 [0x930d7611]
+ ! 1 __CFRunLoopDoObservers (in CoreFoundation) + 81 [0x930e63b1]
+ ! : 1 CFArrayGetCount (in CoreFoundation) + 20 [0x930797f4]
+ ! 1 __CFRunLoopDoObservers (in CoreFoundation) + 194 [0x930e6422]
+ ! 1 CFArrayGetValueAtIndex (in CoreFoundation) + 0 [0x9308ef80]
+ 1 __CFRunLoopRun (in CoreFoundation) + 1550 [0x930d75de]
+ 1 mach_port_extract_member (in libsystem_kernel.dylib) + 31 [0x91bc7363]
+ 1 _kernelrpc_mach_port_extract_member_trap (in libsystem_kernel.dylib) + 10 [0x91bc3f26]