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

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

i getting exc_bad_instruction (code=exc_i386_invop, subcode=0x0) on dispatch_semaphore_dispose don't know how track downwards root cause of this. code makes utilize of dispatch_async, dispatch_group_enter , on.

update: cause of crash due fact webservicecall (see code below) never calls oncompletion , when code run again, got error exc_bad_instruction. verified indeed case, not sure why or how prevent this.

code:

dispatch_queue_t queue = dispatch_get_global_queue(dispatch_queue_priority_high, 0); dispatch_group_t grouping = dispatch_group_create(); (...) { 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, ^{ // phone call completion handler passed in caller }); });

from stack trace, exc_bad_instruction (code=exc_i386_invop, subcode=0x0) occurred because dispatch_group_t released while still locking (waiting dispatch_group_leave).

according found, happened :

dispatch_group_t group created. group's retain count = 1. -[self webservice:oncompletion:] captured group. group's retain count = 2. dispatch_async(...., ^{ dispatch_group_wait(group, ...) ... }); captured group again. group's retain count = 3. exit current scope. group released. group's retain count = 2. dispatch_group_leave never called. dispatch_group_wait timeout. dispatch_async block completed. group released. group's retain count = 1. you called method again. when -[self webservice:oncompletion:] called again, old oncompletion block replaced new one. so, old group released. group's retain count = 0. group deallocated. resulted exc_bad_instruction.

to prepare this, suggest should find out why -[self webservice:oncompletion:] didn't phone call oncompletion block, , prepare it. create sure next phone call method happen after previous phone call did finish.

in case allow method called many times whether previous calls did finish or not, might find hold group :

you can alter timeout 2 seconds dispatch_time_forever or reasonable amount of time -[self webservice:oncompletion] should phone call oncompletion blocks time. block in dispatch_async(...) hold you. or you can add together group collection, such nsmutablearray.

i think the best approach create dedicate class action. when want create calls webservice, create object of class, phone call method on completion block passing release object. in class, there ivar of dispatch_group_t or dispatch_semaphore_t.

ios objective-c exception grand-central-dispatch