title: App hangs at __psynch_mutexwait
body: <p>Our app seems to semi-randomly hang at psynch_mutexwait.
  It seems to be related to a background process that updates a bunch of data stored in CoreData - but I've been completely unable to figure out just who is locking on what to cause the deadlock.</p>
  
  <p>Following is the complete stack trace that lldb gives me - which is obviously incomplete, AND the last frame of Thread 1 is bogus.  I had a breakpoint in that method a few lines before that, and it was never hit.</p>
  
  <p>Is there ANY way of figuring out what lock is being waited on? (or even get correct stack traces?)  Of course there is LOTS of code involved, which makes random NSLog statements a massive undertaking.</p>
  
  <pre><code>(lldb) bt all
  * thread #1: tid = 0x2503, 0x39da20fc libsystem_kernel.dylib`__psynch_mutexwait + 24, stop reason = signal SIGSTOP
      frame #0: 0x39da20fc libsystem_kernel.dylib`__psynch_mutexwait + 24
      frame #1: 0x39ceb128 libsystem_c.dylib`pthread_mutex_lock + 392
      frame #2: 0x00022068 OnDeck`-[AttendanceWorkoutsController buildTable](self=0x00000003, _cmd=0x00000000) + 508 at AttendanceWorkoutsController.m:100
  
    thread #2: tid = 0x2803, 0x39d92648 libsystem_kernel.dylib`kevent64 + 24
      frame #0: 0x39d92648 libsystem_kernel.dylib`kevent64 + 24
      frame #1: 0x39ccb4f0 libdispatch.dylib`_dispatch_mgr_invoke + 796
  
    thread #5: tid = 0x2b03, 0x39d91eb4 libsystem_kernel.dylib`mach_msg_trap + 20
      frame #0: 0x39d91eb4 libsystem_kernel.dylib`mach_msg_trap + 20
      frame #1: 0x39d9204c libsystem_kernel.dylib`mach_msg + 40
  
    thread #6: tid = 0x242f, 0x39d91eb4 libsystem_kernel.dylib`mach_msg_trap + 20
      frame #0: 0x39d91eb4 libsystem_kernel.dylib`mach_msg_trap + 20
      frame #1: 0x39d9204c libsystem_kernel.dylib`mach_msg + 40
  
    thread #7: tid = 0x2c03, 0x39da2594 libsystem_kernel.dylib`select$DARWIN_EXTSN + 20
      frame #0: 0x39da2594 libsystem_kernel.dylib`select$DARWIN_EXTSN + 20
      frame #1: 0x31bff1f6 CoreFoundation`__CFSocketManager + 678
  
    thread #8: tid = 0x2d03, 0x39da2d98 libsystem_kernel.dylib`__workq_kernreturn + 8
      frame #0: 0x39da2d98 libsystem_kernel.dylib`__workq_kernreturn + 8
      frame #1: 0x39cf0cfa libsystem_c.dylib`_pthread_workq_return + 18
  (lldb) 
  </code></pre>