EXC BAD INSTRUCTION code EXC I386 INVOP subcode 0x0 on dispatch semaphore dispose

Question

I am getting EXC BAD INSTRUCTION  code EXC I386 INVOP  subcode 0x0  on dispatch semaphore dispose but don t really know how to track down the root cause of this   My code makes use of dispatch async  dispatch group enter and so on   UPDATE  The cause of the crash is due to the fact that the webserviceCall  see code below  never calls onCompletion and when the code is run again  I got the error EXC BAD INSTRUCTION   I verified this is indeed the case  but not sure why or how to prevent this     Code   dispatch queue t queue   dispatch get global queue DISPATCH QUEUE PRIORITY HIGH  0   dispatch group t group   dispatch group create          for                 if                     dispatch group enter group               dispatch async queue                      self webserviceCall url onCompletion                         dispatch group leave group                                                           dispatch async dispatch get global queue DISPATCH QUEUE PRIORITY DEFAULT  0          dispatch group wait group  dispatch time DISPATCH TIME NOW   int64 t  2 0   NSEC PER SEC         dispatch sync queue                call completion handler passed in by caller

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My problem was took IBOutlet but didn t connect with interface builder and using in swift file

User · Answer

I landed here because of an XCTestCase  in which I d disabled most of the tests by prefixing them with  no   as in no testBackgroundAdding  Once I noticed that most of the answers had something to do with locks and threading  I realized the test contained a few instances of XCTestExpectation with corresponding waitForExpectations  They were all in the disabled tests  but apparently Xcode was still evaluating them at some level    In the end I found an XCTestExpectation that was defined as  property but lacked the  synthesize  Once I added the synthesize directive  the EXC BAD INSTRUCTION disappeared

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My issue was that it was in my init    Probably the  weak self  killed him while the init wasn t finished  I moved it from the init and it solved my issue

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From your stack trace  EXC BAD INSTRUCTION  code EXC I386 INVOP  subcode 0x0  occurred because dispatch group t was released while it was still locking  waiting for dispatch group leave    According to what you found  this was what happened     dispatch group t group was created  group s retain count   1  - self webservice onCompletion   captured the group  group s retain count   2  dispatch async          dispatch group wait group               captured the group again  group s retain count   3  Exit the current scope  group was released  group s retain count   2  dispatch group leave was never called  dispatch group wait was timeout  The dispatch async block was completed  group was released  group s retain count   1  You called this method again  When - self webservice onCompletion   was called again  the old onCompletion block was replaced with the new one  So  the old group was released  group s retain count   0  group was deallocated  That resulted to EXC BAD INSTRUCTION    To fix this  I suggest you should find out why - self webservice onCompletion   didn t call onCompletion block  and fix it  Then make sure the next call to the method will happen after the previous call did finish      In case you allow the method to be called many times whether the previous calls did finish or not  you might find someone to hold group for you      You can change the timeout from 2 seconds to DISPATCH TIME FOREVER or a reasonable amount of time that all - self webservice onCompletion  should call their onCompletion blocks by the time  So that the block in dispatch async      will hold it for you  OR  You can add group into a collection  such as NSMutableArray      I think it is the best approach to create a dedicate class for this action  When you want to make calls to webservice  you then create an object of the class  call the method on it with the completion block passing to it that will release the object  In the class  there is an ivar of dispatch group t or dispatch semaphore t

User · Answer

Sometimes all it takes to get a EXC BAD INSTRUCTION  code EXC I386 INVOP  subcode 0x0  is a missing return statement   It certainly was my case

User · Answer

I had a different issue that brought me to this question  which will probably be more common than the overrelease issue in the accepted answer  Root cause was our completion block being called twice due to bad if else fallthrough in the network handler  leading to two calls of dispatch group leave for every one call to dispatch group enter  Completion block called multiple times  dispatch group enter group    self badMethodThatCallsMULTIPLECompletions   NSString  completion            this block is called multiple times        one  enter  but multiple  leave       dispatch group leave group        Debug via the dispatch group s count Upon the EXC BAD INSTRUCTION  you should still have access to your dispatch group in the debugger  DispatchGroup  check how many  quot entered quot  Print out the dispatch group and you ll see   lt OS dispatch group  group 0x60800008bf40      xrefcnt   0x2  refcnt   0x1  port   0x0  count   -1  waiters   0   gt  When you see count   -1 it indicates that you ve over-left the dispatch group  Be sure to dispatch enter and dispatch leave the group in matched pairs

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In my case       PHImageRequestOptions  requestOptions    PHImageRequestOptions new   requestOptions synchronous              NO    Was trying to do this with dispatch group

User · Answer

My issue was that I was creating objects that I wanted to be stored in a NSMutableDictionary but I never initialized the dictionary   Therefore the objects were getting deleted by garbage collection and breaking later   Check that you have at least one strong reference to the objects youre interacting with

[ios] EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0) on dispatch_semaphore_dispose

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