Unknown crash reason (with CrashReport attached) SIGTRAP. AFNetworking?

Question

I keep getting these crashes in my app that´s in the AppStore. The CrashReport always looks like this:

Incident Identifier: 986486D7-F013-4102-B9E3-84F923223914
CrashReporter Key:   [TODO]
Hardware Model:      iPhone4,1
Process:         MyApp [57885]
Path:            /Users/USER/MyApp.app/MyApp
Identifier:      de.myapp.iphone
Version:         12475
Code Type:       ARM
Parent Process:  launchd [1]

Date/Time:       2012-12-20 15:48:53 +0000
OS Version:      iPhone OS 6.0.1 (10A523)
Report Version:  104

Exception Type:  SIGTRAP
Exception Codes: #0 at 0x3abd62be
Crashed Thread:  0

Thread 0 Crashed:
0   CoreFoundation                      0x363582be CFRelease + 18
1   WebCore                             0x383de395 WebCore::stopSharedTimer() + 33
2   WebCore                             0x38433515 WebCore::TimerBase::~TimerBase() + 45
3   WebCore                             0x3846003b WebCore::Document::~Document() + 2751
4   WebCore                             0x3845f56d WebCore::HTMLDocument::~HTMLDocument() + 81
5   WebCore                             0x384e9473 WebCore::JSNodeOwner::finalize(JSC::Handle<JSC::Unknown>, void*) + 79
6   JavaScriptCore                      0x321e2067 JSC::WeakBlock::sweep() + 87
7   JavaScriptCore                      0x321e22ad JSC::WeakSet::sweep() + 53
8   JavaScriptCore                      0x3213d877 JSC::Heap::collect(JSC::Heap::SweepToggle) + 175
9   JavaScriptCore                      0x3213cad9 JSC::DefaultGCActivityCallbackPlatformData::timerDidFire(__CFRunLoopTimer*, void*) + 145
10  CoreFoundation                      0x363ec5df __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 15
11  CoreFoundation                      0x363ec291 __CFRunLoopDoTimer + 273
12  CoreFoundation                      0x363eaf01 __CFRunLoopRun + 1233
13  CoreFoundation                      0x3635debd CFRunLoopRunSpecific + 357
14  CoreFoundation                      0x3635dd49 CFRunLoopRunInMode + 105
15  GraphicsServices                    0x3490e2eb GSEventRunModal + 75
16  UIKit                               0x37b2b2f9 UIApplicationMain + 1121
17  MyApp                               0x00003927 main (main.m:20)

Thread 5:
0   libsystem_kernel.dylib              0x3681feb4 mach_msg_trap + 20
1   CoreFoundation                      0x363ec045 __CFRunLoopServiceMachPort + 129
2   CoreFoundation                      0x363eada3 __CFRunLoopRun + 883
3   CoreFoundation                      0x3635debd CFRunLoopRunSpecific + 357
4   CoreFoundation                      0x3635dd49 CFRunLoopRunInMode + 105
5   Foundation                          0x307f978f -[NSRunLoop(NSRunLoop) runMode:beforeDate:] + 255
6   Foundation                          0x3089d05d -[NSRunLoop(NSRunLoop) run] + 81
7   MyApp                               0x000c3225 +[AFURLConnectionOperation networkRequestThreadEntryPoint:] (AFURLConnectionOperation.m:157)
8   Foundation                          0x308a667d __NSThread__main__ + 973
9   libsystem_c.dylib                   0x33ab5311 _pthread_start + 309

Thread 6:
0   libsystem_kernel.dylib              0x3681feb4 mach_msg_trap + 20
1   CoreFoundation                      0x363ec045 __CFRunLoopServiceMachPort + 129
2   CoreFoundation                      0x363eada3 __CFRunLoopRun + 883
3   CoreFoundation                      0x3635debd CFRunLoopRunSpecific + 357
4   CoreFoundation                      0x3635dd49 CFRunLoopRunInMode + 105
5   Foundation                          0x30822bcd +[NSURLConnection(Loader) _resourceLoadLoop:] + 309
6   Foundation                          0x308a667d __NSThread__main__ + 973
7   libsystem_c.dylib                   0x33ab5311 _pthread_start + 309

Thread 7:
0   libsystem_kernel.dylib              0x368300fc __psynch_mutexwait + 24
1   CFNetwork                           0x3137647f __CFURLCache::ExecuteSQLSelectAndCreateResponse(__CFString const*, bool) + 179
2   CFNetwork                           0x313763b1 __CFURLCache::LookupCachedURLResponse(__CFURLCacheNode*, bool) + 13
3   CFNetwork                           0x31387893 __CFURLCache::CopyResponseForRequest(_CFURLRequest const*, bool) + 231
4   CFNetwork                           0x313c2ee1 __CFURLCacheCopyResponseForRequestInternal(_CFURLCache const*, _CFURLRequest const*, unsigned char) + 33
5   CFNetwork                           0x313fe8bd ___loaderEvent_StartLoad_block_invoke_0 + 45
6   CFNetwork                           0x3141e657 ConnectionSession::withStorageSession(void ( block_pointer)(StorageSession const*)) const + 83
7   CFNetwork                           0x313ff9d5 __withStorageSessionAsync_block_invoke_0 + 17
8   CFNetwork                           0x313d3639 __withConnectionSessionAsync_block_invoke_0 + 17
9   libdispatch.dylib                   0x3807711f _dispatch_call_block_and_release + 11
10  libdispatch.dylib                   0x3807b961 _dispatch_root_queue_drain + 253
11  libdispatch.dylib                   0x3807bac1 _dispatch_worker_thread2 + 85
12  libsystem_c.dylib                   0x33aaaa11 _pthread_wqthread + 361

Thread 8:
0   libsystem_kernel.dylib              0x368300fc __psynch_mutexwait + 24
1   CFNetwork                           0x3137647f __CFURLCache::ExecuteSQLSelectAndCreateResponse(__CFString const*, bool) + 179
2   CFNetwork                           0x313763b1 __CFURLCache::LookupCachedURLResponse(__CFURLCacheNode*, bool) + 13
3   CFNetwork                           0x31387893 __CFURLCache::CopyResponseForRequest(_CFURLRequest const*, bool) + 231
4   CFNetwork                           0x313c2ee1 __CFURLCacheCopyResponseForRequestInternal(_CFURLCache const*, _CFURLRequest const*, unsigned char) + 33
5   CFNetwork                           0x313fe8bd ___loaderEvent_StartLoad_block_invoke_0 + 45
6   CFNetwork                           0x3141e657 ConnectionSession::withStorageSession(void ( block_pointer)(StorageSession const*)) const + 83
7   CFNetwork                           0x313ff9d5 __withStorageSessionAsync_block_invoke_0 + 17
8   CFNetwork                           0x313d3639 __withConnectionSessionAsync_block_invoke_0 + 17
9   libdispatch.dylib                   0x3807711f _dispatch_call_block_and_release + 11
10  libdispatch.dylib                   0x3807b961 _dispatch_root_queue_drain + 253
11  libdispatch.dylib                   0x3807bac1 _dispatch_worker_thread2 + 85
12  libsystem_c.dylib                   0x33aaaa11 _pthread_wqthread + 361

Thread 10:
0   libsystem_kernel.dylib              0x368300fc __psynch_mutexwait + 24
1   CFNetwork                           0x3137647f __CFURLCache::ExecuteSQLSelectAndCreateResponse(__CFString const*, bool) + 179
2   CFNetwork                           0x313763b1 __CFURLCache::LookupCachedURLResponse(__CFURLCacheNode*, bool) + 13
3   CFNetwork                           0x31387893 __CFURLCache::CopyResponseForRequest(_CFURLRequest const*, bool) + 231
4   CFNetwork                           0x313c2ee1 __CFURLCacheCopyResponseForRequestInternal(_CFURLCache const*, _CFURLRequest const*, unsigned char) + 33
5   CFNetwork                           0x313fe8bd ___loaderEvent_StartLoad_block_invoke_0 + 45
6   CFNetwork                           0x3141e657 ConnectionSession::withStorageSession(void ( block_pointer)(StorageSession const*)) const + 83
7   CFNetwork                           0x313ff9d5 __withStorageSessionAsync_block_invoke_0 + 17
8   CFNetwork                           0x313d3639 __withConnectionSessionAsync_block_invoke_0 + 17
9   libdispatch.dylib                   0x3807711f _dispatch_call_block_and_release + 11
10  libdispatch.dylib                   0x3807b961 _dispatch_root_queue_drain + 253
11  libdispatch.dylib                   0x3807bac1 _dispatch_worker_thread2 + 85
12  libsystem_c.dylib                   0x33aaaa11 _pthread_wqthread + 361

Thread 13:
0   libsystem_kernel.dylib              0x3682239c pread + 20
1   libsqlite3.dylib                    0x33978109 sqlite3_get_table + 125
2   libsqlite3.dylib                    0x339772a7 sqlite3_get_table + 125
3   libsqlite3.dylib                    0x33d25fb1 0x33cde000 + 294833
4   libsqlite3.dylib                    0x33d13807 0x33cde000 + 219143
5   libsqlite3.dylib                    0x33d0d49d 0x33cde000 + 193693
6   libsqlite3.dylib                    0x3398648f sqlite3_step + 2143
7   CFNetwork                           0x3138276b __CFURLCache::DoBulkLookupAndStoreBasedOnTime(__CFString const*) + 459
8   CFNetwork                           0x313c4667 __ExecuteSQLSelectAndCreateResponse_block_invoke_0 + 35
9   libdispatch.dylib                   0x3807711f _dispatch_call_block_and_release + 11
10  libdispatch.dylib                   0x3807b961 _dispatch_root_queue_drain + 253
11  libdispatch.dylib                   0x3807bac1 _dispatch_worker_thread2 + 85
12  libsystem_c.dylib                   0x33aaaa11 _pthread_wqthread + 361

Thread 17:
0   libsystem_kernel.dylib              0x3683008c __psynch_cvwait + 24
1   libsystem_c.dylib                   0x33aadaa5 pthread_cond_timedwait + 45
2   JavaScriptCore                      0x320d6c75 WTF::ThreadCondition::timedWait(WTF::Mutex&, double) + 109
3   JavaScriptCore                      0x321e8557 JSC::BlockAllocator::blockFreeingThreadMain() + 83
4   JavaScriptCore                      0x321fafab _ZN3WTFL19wtfThreadEntryPointEPv + 15
5   libsystem_c.dylib                   0x33ab5311 _pthread_start + 309

Thread 18:
0   libsystem_kernel.dylib              0x3683008c __psynch_cvwait + 24
1   libsystem_c.dylib                   0x33ab7f19 pthread_cond_wait + 41
2   JavaScriptCore                      0x3217bf41 JSC::SlotVisitor::drainFromShared(JSC::SlotVisitor::SharedDrainMode) + 149
3   JavaScriptCore                      0x3217be81 JSC::MarkStackThreadSharedData::markingThreadMain() + 145
4   JavaScriptCore                      0x321fafab _ZN3WTFL19wtfThreadEntryPointEPv + 15
5   libsystem_c.dylib                   0x33ab5311 _pthread_start + 309

Thread 22:
0   libsystem_kernel.dylib              0x368300fc __psynch_mutexwait + 24
1   CFNetwork                           0x3137647f __CFURLCache::ExecuteSQLSelectAndCreateResponse(__CFString const*, bool) + 179
2   CFNetwork                           0x313763b1 __CFURLCache::LookupCachedURLResponse(__CFURLCacheNode*, bool) + 13
3   CFNetwork                           0x31387893 __CFURLCache::CopyResponseForRequest(_CFURLRequest const*, bool) + 231
4   CFNetwork                           0x313c2ee1 __CFURLCacheCopyResponseForRequestInternal(_CFURLCache const*, _CFURLRequest const*, unsigned char) + 33
5   CFNetwork                           0x313fe8bd ___loaderEvent_StartLoad_block_invoke_0 + 45
6   CFNetwork                           0x3141e657 ConnectionSession::withStorageSession(void ( block_pointer)(StorageSession const*)) const + 83
7   CFNetwork                           0x313ff9d5 __withStorageSessionAsync_block_invoke_0 + 17
8   CFNetwork                           0x313d3639 __withConnectionSessionAsync_block_invoke_0 + 17
9   libdispatch.dylib                   0x3807711f _dispatch_call_block_and_release + 11
10  libdispatch.dylib                   0x3807b961 _dispatch_root_queue_drain + 253
11  libdispatch.dylib                   0x3807bac1 _dispatch_worker_thread2 + 85
12  libsystem_c.dylib                   0x33aaaa11 _pthread_wqthread + 361

Thread 25:
0   libsystem_kernel.dylib              0x368300fc __psynch_mutexwait + 24
1   CFNetwork                           0x3137647f __CFURLCache::ExecuteSQLSelectAndCreateResponse(__CFString const*, bool) + 179
2   CFNetwork                           0x313763b1 __CFURLCache::LookupCachedURLResponse(__CFURLCacheNode*, bool) + 13
3   CFNetwork                           0x31387893 __CFURLCache::CopyResponseForRequest(_CFURLRequest const*, bool) + 231
4   CFNetwork                           0x313c2ee1 __CFURLCacheCopyResponseForRequestInternal(_CFURLCache const*, _CFURLRequest const*, unsigned char) + 33
5   CFNetwork                           0x313fe8bd ___loaderEvent_StartLoad_block_invoke_0 + 45
6   CFNetwork                           0x3141e657 ConnectionSession::withStorageSession(void ( block_pointer)(StorageSession const*)) const + 83
7   CFNetwork                           0x313ff9d5 __withStorageSessionAsync_block_invoke_0 + 17
8   CFNetwork                           0x313d3639 __withConnectionSessionAsync_block_invoke_0 + 17
9   libdispatch.dylib                   0x3807711f _dispatch_call_block_and_release + 11
10  libdispatch.dylib                   0x3807b961 _dispatch_root_queue_drain + 253
11  libdispatch.dylib                   0x3807bac1 _dispatch_worker_thread2 + 85
12  libsystem_c.dylib                   0x33aaaa11 _pthread_wqthread + 361

Thread 43:
0   libsystem_kernel.dylib              0x3682239c pread + 20
1   libsqlite3.dylib                    0x33978109 sqlite3_get_table + 125
2   libsqlite3.dylib                    0x339772a7 sqlite3_get_table + 125
3   libsqlite3.dylib                    0x33d25fb1 0x33cde000 + 294833
4   libsqlite3.dylib                    0x33d13807 0x33cde000 + 219143
5   libsqlite3.dylib                    0x33d0d49d 0x33cde000 + 193693
6   libsqlite3.dylib                    0x3398648f sqlite3_step + 2143
7   CFNetwork                           0x3138276b __CFURLCache::DoBulkLookupAndStoreBasedOnTime(__CFString const*) + 459
8   CFNetwork                           0x313c4667 __ExecuteSQLSelectAndCreateResponse_block_invoke_0 + 35
9   libdispatch.dylib                   0x3807711f _dispatch_call_block_and_release + 11
10  libdispatch.dylib                   0x3807b961 _dispatch_root_queue_drain + 253
11  libdispatch.dylib                   0x3807bac1 _dispatch_worker_thread2 + 85
12  libsystem_c.dylib                   0x33aaaa11 _pthread_wqthread + 361

Thread 44:
0   libsystem_kernel.dylib              0x368300fc __psynch_mutexwait + 24
1   CFNetwork                           0x31382619 __CFURLCache::DoBulkLookupAndStoreBasedOnTime(__CFString const*) + 121
2   CFNetwork                           0x313c4667 __ExecuteSQLSelectAndCreateResponse_block_invoke_0 + 35
3   libdispatch.dylib                   0x3807711f _dispatch_call_block_and_release + 11
4   libdispatch.dylib                   0x3807b961 _dispatch_root_queue_drain + 253
5   libdispatch.dylib                   0x3807bac1 _dispatch_worker_thread2 + 85
6   libsystem_c.dylib                   0x33aaaa11 _pthread_wqthread + 361

Thread 47:
0   libsystem_kernel.dylib              0x368300fc __psynch_mutexwait + 24
1   CFNetwork                           0x3137647f __CFURLCache::ExecuteSQLSelectAndCreateResponse(__CFString const*, bool) + 179
2   CFNetwork                           0x313763b1 __CFURLCache::LookupCachedURLResponse(__CFURLCacheNode*, bool) + 13
3   CFNetwork                           0x31387893 __CFURLCache::CopyResponseForRequest(_CFURLRequest const*, bool) + 231
4   CFNetwork                           0x313c2ee1 __CFURLCacheCopyResponseForRequestInternal(_CFURLCache const*, _CFURLRequest const*, unsigned char) + 33
5   CFNetwork                           0x313fe8bd ___loaderEvent_StartLoad_block_invoke_0 + 45
6   CFNetwork                           0x3141e657 ConnectionSession::withStorageSession(void ( block_pointer)(StorageSession const*)) const + 83
7   CFNetwork                           0x313ff9d5 __withStorageSessionAsync_block_invoke_0 + 17
8   CFNetwork                           0x313d3639 __withConnectionSessionAsync_block_invoke_0 + 17
9   libdispatch.dylib                   0x3807711f _dispatch_call_block_and_release + 11
10  libdispatch.dylib                   0x3807b961 _dispatch_root_queue_drain + 253
11  libdispatch.dylib                   0x3807bac1 _dispatch_worker_thread2 + 85
12  libsystem_c.dylib                   0x33aaaa11 _pthread_wqthread + 361

Thread 49:
0   libsystem_kernel.dylib              0x368300fc __psynch_mutexwait + 24
1   CFNetwork                           0x3137647f __CFURLCache::ExecuteSQLSelectAndCreateResponse(__CFString const*, bool) + 179
2   CFNetwork                           0x313763b1 __CFURLCache::LookupCachedURLResponse(__CFURLCacheNode*, bool) + 13
3   CFNetwork                           0x31387893 __CFURLCache::CopyResponseForRequest(_CFURLRequest const*, bool) + 231
4   CFNetwork                           0x313c2ee1 __CFURLCacheCopyResponseForRequestInternal(_CFURLCache const*, _CFURLRequest const*, unsigned char) + 33
5   CFNetwork                           0x313fe8bd ___loaderEvent_StartLoad_block_invoke_0 + 45
6   CFNetwork                           0x3141e657 ConnectionSession::withStorageSession(void ( block_pointer)(StorageSession const*)) const + 83
7   CFNetwork                           0x313ff9d5 __withStorageSessionAsync_block_invoke_0 + 17
8   CFNetwork                           0x313d3639 __withConnectionSessionAsync_block_invoke_0 + 17
9   libdispatch.dylib                   0x3807711f _dispatch_call_block_and_release + 11
10  libdispatch.dylib                   0x3807b961 _dispatch_root_queue_drain + 253
11  libdispatch.dylib                   0x3807bac1 _dispatch_worker_thread2 + 85
12  libsystem_c.dylib                   0x33aaaa11 _pthread_wqthread + 361

Thread 50:
0   libsystem_kernel.dylib              0x368300fc __psynch_mutexwait + 24
1   CFNetwork                           0x3137647f __CFURLCache::ExecuteSQLSelectAndCreateResponse(__CFString const*, bool) + 179
2   CFNetwork                           0x313763b1 __CFURLCache::LookupCachedURLResponse(__CFURLCacheNode*, bool) + 13
3   CFNetwork                           0x31387893 __CFURLCache::CopyResponseForRequest(_CFURLRequest const*, bool) + 231
4   CFNetwork                           0x313c2ee1 __CFURLCacheCopyResponseForRequestInternal(_CFURLCache const*, _CFURLRequest const*, unsigned char) + 33
5   CFNetwork                           0x313fe8bd ___loaderEvent_StartLoad_block_invoke_0 + 45
6   CFNetwork                           0x3141e657 ConnectionSession::withStorageSession(void ( block_pointer)(StorageSession const*)) const + 83
7   CFNetwork                           0x313ff9d5 __withStorageSessionAsync_block_invoke_0 + 17
8   CFNetwork                           0x313d3639 __withConnectionSessionAsync_block_invoke_0 + 17
9   libdispatch.dylib                   0x3807711f _dispatch_call_block_and_release + 11
10  libdispatch.dylib                   0x3807b961 _dispatch_root_queue_drain + 253
11  libdispatch.dylib                   0x3807bac1 _dispatch_worker_thread2 + 85
12  libsystem_c.dylib                   0x33aaaa11 _pthread_wqthread + 361

Thread 51:
0   libsystem_kernel.dylib              0x36830d98 __workq_kernreturn + 8
1   libsystem_c.dylib                   0x33aaaa16 _pthread_wqthread + 366

Thread 0 crashed with ARM Thread State:
    r0: 0x00000000     r1: 0x5df80157     r2: 0x1ddd4000     r3: 0x38596026 
    r4: 0x3be2c86c     r5: 0x00000000     r6: 0x00000000     r7: 0x2fd1be1c 
    r8: 0x00000000     r9: 0x00293498    r10: 0x00388800    r11: 0x04432d90 
    ip: 0x3bd68a50     sp: 0x2fd1bde8     lr: 0x368ba395     pc: 0x3abd62be 
  cpsr: 0x60000030 

I´m basically using an AFJSONRequestOperation in a UIViewController, which has been pushed onto a NavigationController to fetch a JSON it display its contents. Is it AFNetworking that´s causing the crash (in Thread 5)? Or could it be a flaw in my code? I´m really stuck and it happens quite often. Any help or questions very much appreciated!

Fatherly

Did you try symbolicating the crash? – Angelesangelfish

It says "Crashed Thread: 0". Of course, threading gets complicated and maybe there's some weird interaction going on, but it looks as though some JavaScript gets into difficulty... – Sedimentology

Tried finding zombie with Instruments ? History of the zombie object could give some clues... – Gymno

@Lukas The crash is already symbolicated. user1885297: I can´t check that, because it´s not connected to any debugger. These are crash reports from a live system, gathered with PLCrashReporter. Stephen Darlington: I´m not using any JavaScript at any place in my App. – Fatherly

Are you using a UIWebView ? Otherwise, the reference to HTMLDocument doesn't make sense. Also, do you have access to console log ? Any message logged in there ? – Gymno

I´m using an Ad-Library that itself uses a WebView (smartadserver.com) and a WebViewController (github.com/samvermette/SVWebViewController). Besides that, I´m using Erica Sadun´s MarkupHelper (github.com/erica/iOS-5-Cookbook/blob/master/C10/17-PDF%20Pages/…) to translate HTML into AttributedStrings. So there are many possibilities. The only chance one of this could run together with an AFURLOperation would be in the case of MarkupHelper, assuming none of the others use AFNetworking for themselves. Hmm... – Fatherly

Some thoughts. It is unlikely that MarkupHelper is involved as it is only a string utility. And, there is no AF operation is progress; Thread 5 is just listening in for delegate callbacks, and runs all the time, once a AF operation has been started. I'd focus on the Ad library. – Gymno

Did you ever figure out what was going on?. I'm having the exact same crashlog. Thanks! – Larger

not yet, sorry...but I blamed the ad-library for it. :) – Fatherly

I'll keep digging then. Thanks for your reply!. – Larger

Seeing this exact same crash when running our app in the simulator periodically. No idea what's causing it. – Rip

I'm having the exact same crash atm, and am suspecting Google Maps. Are you using Google Maps as well? – Doud

We are dealing with a crash that shows the exact same stack trace as this one. We're NOT using map functionality or the Ad-Library, so that's probably not it. We are using a UIWebView at startup. If/when I figure out what's doing this on our app, I'll post details. – Trinette

More random thoughts: Remaining delegates on previous controllers, or bad parseing of the request (if you are not receiving what you are waiting for). A little code here would be great. – Ruskin

Answer 1

Its not a problem with Thread 5 according to the crash; it is a problem in Thread 0.

Brian in his blog posting adds some background information on how the timer operates in webkit.

http://brrian.tumblr.com/post/13951629341/how-webkits-event-model-works

Its interesting that the problem OS is 6.0.1, not the newer version 6.1, nor 7.x (as of the time of writing).

The crash happens during a CFRelease, and this tends to happen when a resource has already been released is released. My suggestion is to see if the problem happens on any newer OS as it sounds like a WebKit bug. Webkit is the code responsible for the timer.

The timer code has been re-worked anyhow: https://trac.webkit.org/changeset/143210

So I think the best option is to look to see if the newest iOS ever has this crash, or the newest 6.x (6.1).

Failing this, and assuming you cannot reproduce the problem, since you have networking queries (and DB queries) going on, the classic way timers come into the picture is when you have slow/unreliable network connection. Use Apple's Network Link Conditioner to simulate such conditions. This might show up the problem in WebKit.

Ramsdell

Answer 2

Check if some ad opened the iTunes. Maybe you are opening too many threads in the initialization of your application. You can try to enqueue these requests. Just random thoughts..

Undergraduate