Is this crash in libdispatch caused by Reachability?

Question

Can anyone tell me if this crashing stack appears to be caused by Reachability? I am running apple's latest implementation of Reachability, downloadable at https://developer.apple.com/library/ios/samplecode/reachability/Introduction/Intro.html

I have an app where ARC is not enabled by default (it is a legacy app) but I enable it on a per-file basis. I have enabled -fobjc-arc for Reachability.m

When I look at these threads, my code is nowhere to be found. I see some activity happening because of a WebHTMLView (probably the ad network view code currently on screen; it's not mine).

On Thread 10, I see a SCNetworkReachabilityDeallocate, then a dispatch_semaphore_wait_slow, and the crash happens on Thread 14 in libdispatch.

Do you think this crash is being caused by that Reachability code, and have I erred in using -fobjc-arc with Reachability.m?

Exception Type:  EXC_BAD_ACCESS (SIGSEGV)
Exception Subtype: KERN_INVALID_ADDRESS at 0x2000000c
Triggered by Thread:  14

Thread 0:
0   libsystem_kernel.dylib          0x39cafa84 mach_msg_trap + 20
1   libsystem_kernel.dylib          0x39caf87c mach_msg + 36
2   CoreFoundation                  0x2f3e255c __CFRunLoopServiceMachPort + 152
3   CoreFoundation                  0x2f3e0cc2 __CFRunLoopRun + 858
4   CoreFoundation                  0x2f34b53c CFRunLoopRunSpecific + 520
5   CoreFoundation                  0x2f34b31e CFRunLoopRunInMode + 102
6   GraphicsServices                0x340822e6 GSEventRunModal + 134
7   UIKit                           0x31c021e0 UIApplicationMain + 1132
8   MyApp                           0x00053ad4 main (main.m:33)
9   libdyld.dylib                   0x39c0bab4 start + 0

Thread 1:
0   libsystem_kernel.dylib          0x39caf838 kevent64 + 24
1   libdispatch.dylib               0x39bfe0d0 _dispatch_mgr_invoke + 228
2   libdispatch.dylib               0x39bf863e _dispatch_mgr_thread + 34

Thread 2 name:  com.apple.NSURLConnectionLoader
Thread 2:
0   libsystem_kernel.dylib          0x39cb0910 close + 8
1   CoreFoundation                  0x2f370ef6 CFSocketInvalidate + 434
2   CFNetwork                       0x2f0122a2 Schedulables::_SchedulablesInvalidateApplierFunction(void const*, void*) + 14
3   CoreFoundation                  0x2f34af6e CFArrayApplyFunction + 34
4   CFNetwork                       0x2f011a94 SocketStream::close(void const*) + 280
5   CFNetwork                       0x2f01194e CoreStreamBase::_streamInterface_Close() + 46
6   CFNetwork                       0x2f030286 HTTPReadFilter::_streamImpl_Close() + 66
7   CFNetwork                       0x2f01194e CoreStreamBase::_streamInterface_Close() + 46
8   CFNetwork                       0x2f0301c6 NetConnection::shutdownConnectionStreams() + 98
9   CFNetwork                       0x2f0309c8 NetConnection::closeStreamsIfPossibleOrSignalThatThatNeedsToBeDonePrettyPlease() + 56
10  CFNetwork                       0x2f030d12 HTTPConnectionCacheEntry::removeUnauthConnection(NetConnection*) + 182
11  CoreFoundation                  0x2f34af6e CFArrayApplyFunction + 34
12  CFNetwork                       0x2f075678 HTTPConnectionCacheEntry::purgeIdleConnections(double, double) + 256
13  CFNetwork                       0x2f030ad4 HTTPConnectionCache::performIdleSweep() + 156
14  CFNetwork                       0x2f073b42 HTTPConnectionCache::timeoutIdleCellConnections() + 18
15  CFNetwork                       0x2f0b3394 ___ZNK17CoreSchedulingSet13_performAsyncEPKcU13block_pointerFvvE_block_invoke + 16
16  CoreFoundation                  0x2f34af6e CFArrayApplyFunction + 34
17  CFNetwork                       0x2f019f10 RunloopBlockContext::perform() + 160
18  CFNetwork                       0x2f019de2 MultiplexerSource::perform() + 218
19  CFNetwork                       0x2f019c70 MultiplexerSource::_perform(void*) + 44
20  CoreFoundation                  0x2f3e2f24 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 12
21  CoreFoundation                  0x2f3e23ea __CFRunLoopDoSources0 + 202
22  CoreFoundation                  0x2f3e0bda __CFRunLoopRun + 626
23  CoreFoundation                  0x2f34b53c CFRunLoopRunSpecific + 520
24  CoreFoundation                  0x2f34b31e CFRunLoopRunInMode + 102
25  Foundation                      0x2fd8664c +[NSURLConnection(Loader) _resourceLoadLoop:] + 316
26  Foundation                      0x2fdfbdc2 __NSThread__main__ + 1058
27  libsystem_pthread.dylib         0x39d28c5a _pthread_body + 138
28  libsystem_pthread.dylib         0x39d28bca _pthread_start + 98
29  libsystem_pthread.dylib         0x39d26ccc thread_start + 4

Thread 3 name:  WebThread
Thread 3:
0   CoreGraphics                    0x2f49163c CGRectIsEmpty + 0
1   WebCore                         0x37291700 -[WAKView setNeedsDisplayInRect:] + 76
2   WebKit                          0x37cad22a -[WebHTMLView setNeedsDisplayInRect:] + 214
3   WebCore                         0x372915cc WebCore::ScrollView::platformRepaintContentRectangle(WebCore::IntRect const&, bool) + 148
4   WebCore                         0x37291412 WebCore::ScrollView::repaintContentRectangle(WebCore::IntRect const&, bool) + 98
5   WebCore                         0x37291272 WebCore::FrameView::doDeferredRepaints() + 90
6   WebCore                         0x372dc96c WebCore::FrameView::layout(bool) + 1748
7   WebCore                         0x3721fb94 WebCore::ThreadTimers::sharedTimerFiredInternal() + 132
8   WebCore                         0x3721fae6 WebCore::timerFired(__CFRunLoopTimer*, void*) + 22
9   CoreFoundation                  0x2f3e2e84 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 12
10  CoreFoundation                  0x2f3e2a9e __CFRunLoopDoTimer + 790
11  CoreFoundation                  0x2f3e0e26 __CFRunLoopRun + 1214
12  CoreFoundation                  0x2f34b53c CFRunLoopRunSpecific + 520
13  CoreFoundation                  0x2f34b31e CFRunLoopRunInMode + 102
14  WebCore                         0x372ae7d8 RunWebThread(void*) + 416
15  libsystem_pthread.dylib         0x39d28c5a _pthread_body + 138
16  libsystem_pthread.dylib         0x39d28bca _pthread_start + 98
17  libsystem_pthread.dylib         0x39d26ccc thread_start + 4

Thread 4:
0   libsystem_kernel.dylib          0x39cafa84 mach_msg_trap + 20
1   libsystem_kernel.dylib          0x39caf87c mach_msg + 36
2   CoreFoundation                  0x2f3e255c __CFRunLoopServiceMachPort + 152
3   CoreFoundation                  0x2f3e0c7c __CFRunLoopRun + 788
4   CoreFoundation                  0x2f34b53c CFRunLoopRunSpecific + 520
5   CoreFoundation                  0x2f34b31e CFRunLoopRunInMode + 102
6   libAVFAudio.dylib               0x2e3295ae GenericRunLoopThread::Entry(void*) + 126
7   libAVFAudio.dylib               0x2e31dbf4 CAPThread::Entry(CAPThread*) + 176
8   libsystem_pthread.dylib         0x39d28c5a _pthread_body + 138
9   libsystem_pthread.dylib         0x39d28bca _pthread_start + 98
10  libsystem_pthread.dylib         0x39d26ccc thread_start + 4

Thread 5 name:  JavaScriptCore::BlockFree
Thread 5:
0   libsystem_kernel.dylib          0x39cc1f38 __psynch_cvwait + 24
1   libsystem_pthread.dylib         0x39d28262 _pthread_cond_wait + 538
2   libsystem_pthread.dylib         0x39d2903c pthread_cond_wait + 36
3   JavaScriptCore                  0x3036f408 JSC::BlockAllocator::blockFreeingThreadMain() + 204
4   JavaScriptCore                  0x3036ca70 WTF::wtfThreadEntryPoint(void*) + 12
5   libsystem_pthread.dylib         0x39d28c5a _pthread_body + 138
6   libsystem_pthread.dylib         0x39d28bca _pthread_start + 98
7   libsystem_pthread.dylib         0x39d26ccc thread_start + 4

Thread 6 name:  JavaScriptCore::Marking
Thread 6:
0   libsystem_kernel.dylib          0x39cc1f38 __psynch_cvwait + 24
1   libsystem_pthread.dylib         0x39d28262 _pthread_cond_wait + 538
2   libsystem_pthread.dylib         0x39d2903c pthread_cond_wait + 36
3   JavaScriptCore                  0x3050daf2 JSC::GCThread::waitForNextPhase() + 74
4   JavaScriptCore                  0x3050db4c JSC::GCThread::gcThreadMain() + 48
5   JavaScriptCore                  0x3036ca70 WTF::wtfThreadEntryPoint(void*) + 12
6   libsystem_pthread.dylib         0x39d28c5a _pthread_body + 138
7   libsystem_pthread.dylib         0x39d28bca _pthread_start + 98
8   libsystem_pthread.dylib         0x39d26ccc thread_start + 4

Thread 7 name:  com.apple.CFSocket.private
Thread 7:
0   libsystem_kernel.dylib          0x39cc2440 select$DARWIN_EXTSN + 20
1   CoreFoundation                  0x2f3e645e __CFSocketManager + 482
2   libsystem_pthread.dylib         0x39d28c5a _pthread_body + 138
3   libsystem_pthread.dylib         0x39d28bca _pthread_start + 98
4   libsystem_pthread.dylib         0x39d26ccc thread_start + 4

Thread 8 name:  AFNetworking
Thread 8:
0   libsystem_kernel.dylib          0x39cafa84 mach_msg_trap + 20
1   libsystem_kernel.dylib          0x39caf87c mach_msg + 36
2   CoreFoundation                  0x2f3e255c __CFRunLoopServiceMachPort + 152
3   CoreFoundation                  0x2f3e0c7c __CFRunLoopRun + 788
4   CoreFoundation                  0x2f34b53c CFRunLoopRunSpecific + 520
5   CoreFoundation                  0x2f34b31e CFRunLoopRunInMode + 102
6   Foundation                      0x2fd39822 -[NSRunLoop(NSRunLoop) runMode:beforeDate:] + 250
7   Foundation                      0x2fd8a664 -[NSRunLoop(NSRunLoop) run] + 76
8   MyApp                           0x002c33d0 +[AFURLConnectionOperation networkRequestThreadEntryPoint:] (AFURLConnectionOperation.m:184)
9   Foundation                      0x2fdfbdc2 __NSThread__main__ + 1058
10  libsystem_pthread.dylib         0x39d28c5a _pthread_body + 138
11  libsystem_pthread.dylib         0x39d28bca _pthread_start + 98
12  libsystem_pthread.dylib         0x39d26ccc thread_start + 4

Thread 9 name:  WebCore: CFNetwork Loader
Thread 9:
0   libsystem_kernel.dylib          0x39cafa84 mach_msg_trap + 20
1   libsystem_kernel.dylib          0x39caf87c mach_msg + 36
2   CoreFoundation                  0x2f3e255c __CFRunLoopServiceMachPort + 152
3   CoreFoundation                  0x2f3e0c7c __CFRunLoopRun + 788
4   CoreFoundation                  0x2f34b53c CFRunLoopRunSpecific + 520
5   CoreFoundation                  0x2f34b31e CFRunLoopRunInMode + 102
6   WebCore                         0x372f7872 WebCore::runLoaderThread(void*) + 250
7   JavaScriptCore                  0x3036ca70 WTF::wtfThreadEntryPoint(void*) + 12
8   libsystem_pthread.dylib         0x39d28c5a _pthread_body + 138
9   libsystem_pthread.dylib         0x39d28bca _pthread_start + 98
10  libsystem_pthread.dylib         0x39d26ccc thread_start + 4

Thread 10:
0   libsystem_kernel.dylib          0x39cafad4 semaphore_wait_trap + 8
1   libdispatch.dylib               0x39bfcdec _dispatch_semaphore_wait_slow + 172
2   libxpc.dylib                    0x39d370d6 xpc_connection_send_message_with_reply_sync + 150
3   SystemConfiguration             0x31b77362 _reach_server_target_remove + 90
4   SystemConfiguration             0x31b772d2 __SCNetworkReachabilityServer_targetRemove + 38
5   SystemConfiguration             0x31b5e318 __SCNetworkReachabilityDeallocate + 92
6   CoreFoundation                  0x2f347efc CFRelease + 464
7   libdispatch.dylib               0x39bfc7e0 _dispatch_root_queue_drain + 220
8   libdispatch.dylib               0x39bfc9cc _dispatch_worker_thread2 + 52
9   libsystem_pthread.dylib         0x39d26dfc _pthread_wqthread + 296
10  libsystem_pthread.dylib         0x39d26cc0 start_wqthread + 4

Thread 11:
0   libsystem_kernel.dylib          0x39cc2c7c __workq_kernreturn + 8
1   libsystem_pthread.dylib         0x39d26e06 _pthread_wqthread + 306
2   libsystem_pthread.dylib         0x39d26cc0 start_wqthread + 4

Thread 12:
0   libsystem_kernel.dylib          0x39cc2c7c __workq_kernreturn + 8
1   libsystem_pthread.dylib         0x39d26e06 _pthread_wqthread + 306
2   libsystem_pthread.dylib         0x39d26cc0 start_wqthread + 4

Thread 13:
0   libsystem_kernel.dylib          0x39cafa84 mach_msg_trap + 20
1   libsystem_kernel.dylib          0x39caf87c mach_msg + 36
2   CoreFoundation                  0x2f3e255c __CFRunLoopServiceMachPort + 152
3   CoreFoundation                  0x2f3e0c7c __CFRunLoopRun + 788
4   CoreFoundation                  0x2f34b53c CFRunLoopRunSpecific + 520
5   CoreFoundation                  0x2f38f1a6 CFRunLoopRun + 94
6   CoreMotion                      0x2fa03394 ___lldb_unnamed_function1407$$CoreMotion + 724
7   libsystem_pthread.dylib         0x39d28c5a _pthread_body + 138
8   libsystem_pthread.dylib         0x39d28bca _pthread_start + 98
9   libsystem_pthread.dylib         0x39d26ccc thread_start + 4

Thread 14 Crashed:
0   libobjc.A.dylib                 0x3970db66 objc_msgSend + 6
1   CoreFoundation                  0x2f347f58 CFRelease + 556
2   libdispatch.dylib               0x39bf7100 _dispatch_call_block_and_release + 8
3   libdispatch.dylib               0x39bfbe72 _dispatch_queue_drain + 370
4   libdispatch.dylib               0x39bf8f96 _dispatch_queue_invoke + 38
5   libdispatch.dylib               0x39bfc74e _dispatch_root_queue_drain + 74
6   libdispatch.dylib               0x39bfc9cc _dispatch_worker_thread2 + 52
7   libsystem_pthread.dylib         0x39d26dfc _pthread_wqthread + 296
8   libsystem_pthread.dylib         0x39d26cc0 start_wqthread + 4

Seems like it called 'CFRelease' on dangling pointer – Yurii Romanchenko Feb 10 '14 at 11:06 — Yurii Romanchenko, Feb 10 '14 at 11:06

score 0 · Answer 1 · answered Jul 08 '14 at 16:35

This crash could be caused by just about any piece of code, including your own.

The stack trace indicates that a block has previously retained a pointer that is now being released with CFRelease. If the pointer was not properly retained in the first place - or was in the process of being dealloc-ed when it was originally retained, you could see this stack trace.

If you are accessing the pointer on one thread, but releasing it another, then you may well have the kind of race condition that can cause this kind of crash.

Is this crash in libdispatch caused by Reachability?

1 Answers1