0 Replies
      Latest reply on Apr 30, 2020 3:19 AM by Android2Test
      Android2Test Level 1 Level 1 (0 points)

        Hi Experts,

         

        I created a simple deadlock program with dispatch concurrent queue but no label:

         

        dispatch_queue_t queueA = dispatch_queue_create(NULL, DISPATCH_QUEUE_CONCURRENT);

        dispatch_async(queueA, ^(){

                NSLog(@"3:%@",  [NSThread currentThread]);

                dispatch_barrier_sync(queueA, ^(){

                    NSLog(@"4:%@",  [NSThread currentThread]);

                });

            });

         

        the output of sample shows the dispatch queue is serial, not concurrent.

         

        2733 Thread_<multiple>   DispatchQueue_25: (null)  (serial)

              2733 start_wqthread  (in libsystem_pthread.dylib) + 13  [0x1003bce01]

                2733 _pthread_wqthread  (in libsystem_pthread.dylib) + 583  [0x1003bd0b7]

                  2733 _dispatch_worker_thread2  (in libdispatch.dylib) + 125  [0x1003572da]

                    2733 _dispatch_root_queue_drain  (in libdispatch.dylib) + 334  [0x100356824]

                      2733 _dispatch_async_redirect_invoke  (in libdispatch.dylib) + 769  [0x1003463b4]

                        2733 _dispatch_continuation_pop  (in libdispatch.dylib) + 563  [0x1003472be]

                          2733 _dispatch_client_callout  (in libdispatch.dylib) + 8  [0x100343f1b]

                            2733 _dispatch_call_block_and_release  (in libdispatch.dylib) + 12  [0x100342e7c]

                              2733 __main_block_invoke_2.14  (in learn_oc) + 125  [0x10000176d]  main.mm:249

                                2733 _dispatch_sync_f_slow  (in libdispatch.dylib) + 223  [0x10035346c]

                                  2733 __DISPATCH_WAIT_FOR_QUEUE__  (in libdispatch.dylib) + 301  [0x100353c90]

                                    2733 _dispatch_thread_event_wait_slow  (in libdispatch.dylib) + 33  [0x1003448ec]

                                      2733 _dispatch_ulock_wait  (in libdispatch.dylib) + 47  [0x10034480d]

                                        2733 __ulock_wait  (in libsystem_kernel.dylib) + 10  [0x7fff7e3e19de]

         

        But if I create the same concurrent queue with the label, the result is correct:

        dispatch_queue_t queueA = dispatch_queue_create("test", DISPATCH_QUEUE_CONCURRENT);

         

        2891 Thread_34199   DispatchQueue_25: test  (concurrent)

            + 2891 start_wqthread  (in libsystem_pthread.dylib) + 13  [0x1003bce01]

            +   2891 _pthread_wqthread  (in libsystem_pthread.dylib) + 583  [0x1003bd0b7]

            +     2891 _dispatch_worker_thread2  (in libdispatch.dylib) + 125  [0x1003572da]

            +       2891 _dispatch_root_queue_drain  (in libdispatch.dylib) + 334  [0x100356824]

            +         2891 _dispatch_async_redirect_invoke  (in libdispatch.dylib) + 769  [0x1003463b4]

            +           2891 _dispatch_continuation_pop  (in libdispatch.dylib) + 563  [0x1003472be]

            +             2891 _dispatch_client_callout  (in libdispatch.dylib) + 8  [0x100343f1b]

            +               2891 _dispatch_call_block_and_release  (in libdispatch.dylib) + 12  [0x100342e7c]

            +                 2891 __main_block_invoke_2.15  (in learn_oc) + 125  [0x10000176d]  main.mm:249

            +                   2891 _dispatch_sync_f_slow  (in libdispatch.dylib) + 223  [0x10035346c]

            +                     2891 __DISPATCH_WAIT_FOR_QUEUE__  (in libdispatch.dylib) + 301  [0x100353c90]

            +                       2891 _dispatch_thread_event_wait_slow  (in libdispatch.dylib) + 33  [0x1003448ec]

            +                         2891 _dispatch_ulock_wait  (in libdispatch.dylib) + 47  [0x10034480d]

            +                           2891 __ulock_wait  (in libsystem_kernel.dylib) + 10  [0x7fff7e3e19de]

         

        It seems like if there is a label in the queue, that means you want to uniquely identify it in debugging tools such as Instruments, sample, stackshots, and crash reports, or else the system somehow would change the queue?