Breakpoint for "Modifying Layout Engine From Background Thread"

Question

I'm getting the dreaded warning:

This application is modifying the autolayout engine from a background thread after the engine was accessed from the main thread. This can lead to engine corruption and weird crashes.

I know what it means (it has been asked several times before) and how to fix it, or should I say I would know, if I had a clue which part of my code is causing it: The warning pops up several times in a row, and only after I haven't been touching the app for a while.

Also, there are no asynchronous operations running (that I'm aware of) whose conclusion could trigger it.

So the question is: Is there a symbolic breakpoint I can set up (akin to the famous 'unsatisfiable layout constraints' one) to catch this?

I have tried the solution provided in this answer (symbolic breakpoint on +[NSException raise:format:]), but it just stops three times for each warning, on some background thread with the following call stacks:

First stop:

Thread 11
   > 0 +[NSException raise:format:] 
     16 start_wqthread

Second stop:

Thread 11
   > 0 objc_exception_throw
     17 start_wqthread

Third stop:

Thread 11
   > 0 __cxa_throw
     20 start_wqthread

The stack logged to the console by the warning, is the following:

Stack:(
    0   CoreFoundation                      0x000000010378834b __exceptionPreprocess + 171
    1   libobjc.A.dylib                     0x00000001031e921e objc_exception_throw + 48
    2   CoreFoundation                      0x00000001037f1265 +[NSException raise:format:] + 197
    3   Foundation                          0x0000000102ee4320 _AssertAutolayoutOnAllowedThreadsOnly + 180
    4   Foundation                          0x0000000102d05be4 -[NSISEngine withBehaviors:performModifications:] + 31
    5   UIKit                               0x0000000105417a42 -[UIView(UIConstraintBasedLayout) _resetLayoutEngineHostConstraints] + 76
    6   UIKit                               0x0000000104b11317 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1192
    7   QuartzCore                          0x00000001047cfcdc -[CALayer layoutSublayers] + 146
    8   QuartzCore                          0x00000001047c37a0 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 366
    9   QuartzCore                          0x00000001047c361e _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 24
    10  QuartzCore                          0x000000010475162c _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 280
    11  QuartzCore                          0x000000010477e713 _ZN2CA11Transaction6commitEv + 475
    12  QuartzCore                          0x000000010477eb91 _ZN2CA11Transaction14release_threadEPv + 593
    13  libsystem_pthread.dylib             0x0000000107f8e50f _pthread_tsd_cleanup + 544
    14  libsystem_pthread.dylib             0x0000000107f8e249 _pthread_exit + 152
    15  libsystem_pthread.dylib             0x0000000107f8c7cd pthread_attr_getschedpolicy + 0
    16  libsystem_pthread.dylib             0x0000000107f8c1ed start_wqthread + 13
)

...neither gives many clues regarding my code.

I know that. I was asking if there is any **meaningful** symbolic breakpoint that can set up, that helps me figure out **which** part of my code exactly is doing that. — Nicolas Miari, Feb 02 '17 at 12:27
I **already** added an exception breakpoint, but it is not helpful. **Please read my question**. — Nicolas Miari, Feb 02 '17 at 12:33
Actually, a symbolic breakpoint on `+[NSException raise:format:]` (which seems to be very similar) — Nicolas Miari, Feb 02 '17 at 12:34
It seems you have added symbolic breakpoint, not exception breakpoint? — Mohammad Zaid Pathan, Feb 02 '17 at 12:36
Actually, I **also** have an exception breakpoint (all exceptions). Neither causes the code to stop at my code, so not very helpful. — Nicolas Miari, Feb 02 '17 at 12:37
I'm not sure it will help, try using *Instruments>Zombie* (press *cmd+I*) — Mohammad Zaid Pathan, Feb 02 '17 at 12:43
@Soumen Not really, I moved on to a different job actually :-) — Nicolas Miari, Oct 11 '17 at 07:07

Breakpoint for "Modifying Layout Engine From Background Thread"

0 Answers0