tons of CFURLCache worker threads?

  • Hello all,

    Does anyone know anything about "com.apple.CFURLCACHE_work_queue" and how many of these queues/threads should be running at once? Normally I wouldn't care about such a detail, and naturally I shouldn't, but I have several collected crash reports where these threads are proliferating.

    All the collected crash reports have about 70-90 waiting threads that look exactly like this:

    > Thread 89:: Dispatch queue: com.apple.CFURLCACHE_work_queue
    > 0  libsystem_kernel.dylib           0x93609c5e semaphore_wait_trap + 10
    > 1  libdispatch.dylib                 0x975c34e4 _dispatch_thread_semaphore_wait + 25
    > 2  libdispatch.dylib                 0x975c2628 _dispatch_barrier_sync_f_slow + 121
    > 3  libdispatch.dylib                 0x975c273c dispatch_barrier_sync_f + 37
    > 4  libdispatch.dylib                 0x975c28c4 dispatch_sync + 45
    > 5  com.apple.CFNetwork               0x9b0f73de _ZL21_CFURLCacheDeallocatePKv + 234
    > 6  com.apple.CoreFoundation         0x9508e1d1 CFRelease + 577
    > 7  com.apple.CFNetwork               0x9b059ee1 ProcessCacheTasks(__CFURLCache*, bool) + 321
    > 8  com.apple.CFNetwork               0x9b059715 _ZL24_CFURLCacheTimerCallbackPv + 721
    > 9  libdispatch.dylib                 0x975bffc9 _dispatch_call_block_and_release + 15
    > 10  libdispatch.dylib                 0x975c194f _dispatch_queue_drain + 224
    > 11  libdispatch.dylib                 0x975c17f4 _dispatch_queue_invoke + 47
    > 12  libdispatch.dylib                 0x975c0ffc _dispatch_worker_thread2 + 187
    > 13  libsystem_c.dylib                 0x98b31b24 _pthread_wqthread + 346
    > 14  libsystem_c.dylib                 0x98b336fe start_wqthread + 30

    None of them are directly crashed. The crash is always some other thread, usually not running any of my own code. An example I've seen more than once:

    > Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
    > 0  ???                               0000000000 0 + 0
    > 1  com.apple.opencl                 0x017501fe PlatformLoadDevice + 1722
    > 2  com.apple.opencl                 0x0174f553 PlatformInitCLCPU + 66
    > 3  libsystem_c.dylib                 0x98b2f487 pthread_once + 76
    > 4  com.apple.opencl                 0x0174f4b1 PlatformInitCL + 61
    > 5  com.apple.opencl                 0x0174f787 clGetDeviceIDs + 223
    > 6  com.apple.opencl                 0x01750f20 clCreateContextFromType + 65
    > 7  com.apple.CoreImage               0x9a379136 ___createCPUclContext_block_invoke_0 + 67
    > 8  libdispatch.dylib                 0x975c3c27 dispatch_once_f + 50
    > 9  libdispatch.dylib                 0x975c3bf0 dispatch_once + 31
    > 10  com.apple.CoreImage               0x9a375ce4 -[FEOpenCLContext initWithOptions:] + 710
    > ...
    > 45  com.apple.HIToolbox               0x97ab116b HIView::Draw(short, OpaqueGrafPtr*, unsigned long) + 81
    > 46  com.apple.HIToolbox               0x97ab1533 HIView::Render(unsigned long, CGContext*) + 45
    > 47  com.apple.HIToolbox               0x97a46ebb WindowData::PrepareForVisibility() + 137
    > 48  com.apple.HIToolbox               0x97cd0fb7 _HIWindowPrepareForVisibility + 29
    > 49  com.apple.HIToolbox               0x97bde7c5 _ZL8DrawMDEFP14MenuSelectData7CGPoint + 698
    > 50  com.apple.HIToolbox               0x97bded50 _ZL11DrawTheMenuP14MenuSelectDataPP9__CFArrayhPh + 622
    > 51  com.apple.HIToolbox               0x97bdf11e _ZL11MenuChangedP14MenuSelectDatahh + 608
    > 52  com.apple.HIToolbox               0x97a4d949 _ZL15TrackMenuCommonR14MenuSelectDataPh + 1235
    > 53  com.apple.HIToolbox               0x97be29a4 _ZL14MenuSelectCoreP8MenuData5PointdmPP13OpaqueMenuRefPt + 420
    > 54  com.apple.HIToolbox               0x97a49bde _HandleMenuSelection2 + 636
    > 55  com.apple.HIToolbox               0x97a4995d _HandleMenuSelection + 53
    > 56  com.apple.AppKit                 0x001cedbc _NSHandleCarbonMenuEvent + 302
    > 57  com.apple.AppKit                 0x0015f6c6 _DPSNextEvent + 2196
    > 58  com.apple.AppKit                 0x0015e942 -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 113
    > 59  com.apple.AppKit                 0x0015acb1 -[NSApplication run] + 911
    > 60  com.apple.AppKit                 0x003ebbd9 NSApplicationMain + 1054
    > 61  com.company.MyApp               0x00005dc1 main + 30
    > 62  com.company.MyApp             0x00001fc5 start + 53

    I don't know what that CoreImage/opencl stuff does, but my suspicion is that my app is running out of a limited resource. Allocated RAM isn't very high, so my best guess is file descriptors, which is why I'm suspicious about all the CFURLCache threads.

    Some additional information: I'm using WebKit (indirectly via NSAttributedString's HTML loading methods) in a background thread to import many HTML files. I've observed that this punts the actual WebKit work to the main thread. My background thread has each HTML load wrapped in an autorelease pool, and I've run leaks (and done heapshot analysis) without turning up any mismanaged resources. I'm also using NSDirectoryEnumerator, but likewise I push/pop an autorelease pool every once in a while (currently once every 25 loop iterations).

    Does anyone have any ideas on where all these CFURLCache threads could be coming from? Or have any other thoughts on my situation?

    Thanks for any ideas!
    ~Martin
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