I’ve found a bug in my application (SymSteam) which I’m having a particularly hard time fixing. It seems that whenever my application is launched as a login item it launches successfully but then crashes just a few seconds later. If the application is launched by the user (i.e. via Finder), it runs normally and doesn’t crash.
Checking Console immediately after logging in, I see the following:
04/08/2012 18:51:47.437 SymSteam[187]: SteamApps exists & SteamAppsSymb exists, suggesting everything is A-OK.
04/08/2012 18:51:47.451 SymSteam[187]: Succesfully started observing everything I need to
04/08/2012 18:51:52.623 com.apple.launchd.peruser.501[124]: ([0x0-0x16016].com.simplecode.SymSteam[187]) Job appears to have crashed: Segmentation fault: 11
The first two lines indicate that the my application started up fine and was able to register for the notifications it needed from NSWorkspace’s notification centre. I can’t figure out what’s causing the segmentation fault though afterwards.
There’s also a crash report too. Here’s an excerpt of it:
OS Version: Mac OS X 10.8 (12A269)
Report Version: 10
Crashed Thread: 0 Dispatch queue: com.apple.main-thread
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: EXC_I386_GPFLT
Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0 libobjc.A.dylib 0x00007fff80902278 _cache_getImp + 4
1 libobjc.A.dylib 0x00007fff80903f51 lookUpMethod + 41
2 libobjc.A.dylib 0x00007fff80905d5e class_respondsToSelector + 31
3 com.apple.CoreFoundation 0x00007fff82adb7ab objectIsKindOfClass + 43
4 com.apple.CoreFoundation 0x00007fff82adb812 __exceptionMatch + 18
5 libobjc.A.dylib 0x00007fff8090d1d4 _objc_exception_do_catch(objc_typeinfo*, objc_typeinfo*, void**, unsigned int) + 144
6 libc++abi.dylib 0x00007fff81621807 get_adjusted_ptr(std::type_info const*, std::type_info const*, void**) + 71
7 libc++abi.dylib 0x00007fff81621439 __gxx_personality_v0 + 889
8 libunwind.dylib 0x00007fff8b678c22 _Unwind_RaiseException + 158
9 libc++abi.dylib 0x00007fff81621baa __cxa_rethrow + 72
10 libobjc.A.dylib 0x00007fff8090d5f5 objc_exception_rethrow + 40
11 com.apple.CoreFoundation 0x00007fff82a7ce36 CFRunLoopRunSpecific + 390
12 com.apple.HIToolbox 0x00007fff8c855774 RunCurrentEventLoopInMode + 209
13 com.apple.HIToolbox 0x00007fff8c855512 ReceiveNextEventCommon + 356
14 com.apple.HIToolbox 0x00007fff8c8553a3 BlockUntilNextEventMatchingListInMode + 62
15 com.apple.AppKit 0x00007fff87afefa3 _DPSNextEvent + 685
16 com.apple.AppKit 0x00007fff87afe862 -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 128
17 com.apple.AppKit 0x00007fff87af5c03 -[NSApplication run] + 517
18 com.apple.AppKit 0x00007fff87a9a656 NSApplicationMain + 869
19 com.simplecode.SymSteam 0x0000000108df4d54 start + 52
Thread 1:
0 libsystem_kernel.dylib 0x00007fff82dad6d6 __workq_kernreturn + 10
1 libsystem_c.dylib 0x00007fff84c27f2c _pthread_workq_return + 25
2 libsystem_c.dylib 0x00007fff84c27cf3 _pthread_wqthread + 412
3 libsystem_c.dylib 0x00007fff84c121b1 start_wqthread + 13
Thread 2:: Dispatch queue: com.apple.libdispatch-manager
0 libsystem_kernel.dylib 0x00007fff82dadd16 kevent + 10
1 libdispatch.dylib 0x00007fff81bafe26 _dispatch_mgr_invoke + 883
2 libdispatch.dylib 0x00007fff81bafa2a _dispatch_mgr_thread + 54
Thread 3:
0 libsystem_kernel.dylib 0x00007fff82dad6d6 __workq_kernreturn + 10
1 libsystem_c.dylib 0x00007fff84c27f2c _pthread_workq_return + 25
2 libsystem_c.dylib 0x00007fff84c27cf3 _pthread_wqthread + 412
3 libsystem_c.dylib 0x00007fff84c121b1 start_wqthread + 13
Thread 4:
0 libsystem_kernel.dylib 0x00007fff82dad6d6 __workq_kernreturn + 10
1 libsystem_c.dylib 0x00007fff84c27f2c _pthread_workq_return + 25
2 libsystem_c.dylib 0x00007fff84c27cf3 _pthread_wqthread + 412
3 libsystem_c.dylib 0x00007fff84c121b1 start_wqthread + 13
Thread 0 crashed with X86 Thread State (64-bit):
rax: 0x1000000000000000 rbx: 0x00007fff70bf5810 rcx: 0x0000000000000001 rdx: 0x0000000000000000
rdi: 0x1000000000000000 rsi: 0x00007fff88323f93 rbp: 0x00007fff56e0b910 rsp: 0x00007fff56e0b8d0
r8: 0x0000000000000000 r9: 0x0000000000000000 r10: 0x00000000510558d1 r11: 0x1000000000000000
r12: 0x0000000000000000 r13: 0x0000000000000000 r14: 0x1000000000000000 r15: 0x00007fff88323f93
rip: 0x00007fff80902278 rfl: 0x0000000000010202 cr2: 0x00007fff88424000
Logical CPU: 0
I’m baffled as to what’s causing the problem since the application doesn’t crash when not launched at login and even when launched at login, it launches but then crashes a few seconds later. I don’t know how to go about debugging this bug either as I can’t set breakpoints or use Instruments on the program since the bug only happens on login.
Any advice on how to go about debugging this is greatly appreciated!
For what it’s worth, my application is a background application (so it doesn’t have a dock icon or main window), it uses the Growl & Sparkle frameworks and it registers for notifications from NSWorkspace when it’s launched.
Update:
Here’s the code that’s executed when my application is launched (some irrelevant code in the applicationDidFinishLaunching: method has been omitted). As I said above, this all gets executed before the crash.
applicationDidFinishLaunching method:
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification{
[self.appController performInitialDriveScan];
[self.appController startWatchingDrives];
}
performInitialDriveScan: simply uses NSFileManager a few times to see if certain directories exist. I won’t post it here since it’s quite long. I’m pretty confident it isn’t the source of the crash.
startWatchingDrives:
- (void)startWatchingDrives{
[[[NSWorkspace sharedWorkspace] notificationCenter] addObserver:self.saController selector:@selector(didMountDrive:) name:NSWorkspaceDidMountNotification object:nil];
[[[NSWorkspace sharedWorkspace] notificationCenter] addObserver:self.saController selector:@selector(didUnMountDrive:) name:NSWorkspaceDidUnmountNotification object:nil];
NSLog(@"Succesfully started observing everything I need to");
}
This just adds an observer to NSWorkspace’s notification centre that watches for drives being mounted/unmounted.
That’s everything that gets executed during the application’s startup. The crash happens after the startWatchingDrives method is called and, as said above, only happens when the application is launched on login. It happens when my application isn’t actually doing anything.
I’ve done a little more debugging and managed to solve my own question. The overall cause of the crash is pretty uninteresting but here it is:
The application is starting up normally when the user logs in and it’s registering for notifications of drive mounts/unmounts from NSWorkspace. Almost immediately after registering for notifications, it receives two notifications for the mounting of /home and /net during login. The
didMountDrive:selector is performed by the notification and within thedidMountDrive:method, I’m trying to get the 3rd path component of the drive that’s just mounted’s URL (since, if it was an external drive being mounted, this would be the name of the drive). That’s where the program crashes since the /home and /net URLs only have two path components, so I’m trying to access an index out of the bounds of the URL’s pathComponents array.The fix was simply to check that there’s at least 3 path components in the URL for the drive that was just mounted.