iphone - objective-c 'double free' error in ARC mode -

i'm trying practice block , gcd/nsoperation, wrote project async-objc, when i'm trying test unit test, encountered 'double free' error, thought there shouldn't such error in arc mode.

here code

- (void)each:(nsarray *)items iterator:(callbackeach)iterator complete:(callbackwitherror)complete {     nsblockoperation *blockop = [nsblockoperation blockoperationwithblock:^{         if (!items || items.count == 0) {             complete(nil);             return;         }          callbackwitherror __block completeonce = complete;         nsoperationqueue *queue = [[nsoperationqueue alloc] init];         nslog(@"start operations %@", queue);         [queue setmaxconcurrentoperationcount:kmaxconcurrentoperationcount];         nsinteger __block count = 0;         (id item in items) {             nsoperation *op = [nsblockoperation blockoperationwithblock:^{                 iterator(item, ^(nserror *error) {                     if (error) {                         completeonce(error);                         completeonce = nil;                     } else {                         count++;                         if (count >= items.count) {                             completeonce(nil);                             completeonce = nil;                         }                     }                 });             }];              [queue addoperation:op];         }          [queue waituntilalloperationsarefinished];         nslog(@"all operations down %@", queue);     }];     [_mainqueue addoperation:blockop]; } 

this test code:

- (void)testeachwithbigdata {     bool __block completed = false;     nsmutablearray *items = [nsmutablearray arraywithcapacity:100];     (int = 1; < 10000; ++i) {         [items addobject:[nsstring stringwithformat:@"%d", i]];     }     nsmutablearray *result = [nsmutablearray arraywithcapacity:100];     [_async each:items         iterator:^(id item, callbackwitherror callback) {             //nslog(@"======item %@", item);             nsnumber *num = [nsnumber numberwithint:[item integervalue]];             //nslog(@"number %@", num);             [result addobject:num];              callback(nil);         }         complete:^(nserror *error) {             dispatch_async(dispatch_get_main_queue(), ^{                 stassertnil(error, @"there should no error");                 [result sortusingcomparator:^nscomparisonresult(id obj1, id obj2) {                     nsnumber *num1 = (nsnumber *)obj1;                     nsnumber *num2 = (nsnumber *)obj2;                     if ([num1 integervalue] > [num2 integervalue]) {                         return nsordereddescending;                     } else if ([num1 integervalue] < [num2 integervalue]) {                         return nsorderedascending;                     }                     return nsorderedsame;                 }];                  nsinteger index = 1;                 (nsnumber *num in result) {                     stassertequals(index, [num integervalue], @"the value should ordered");                     index++;                 }                 completed = yes;             });         }      ];      nsdate *until = [nsdate datewithtimeintervalsincenow:10];     while (!completed && [until timeintervalsincenow] > 0) {         [[nsrunloop currentrunloop] runmode:nsdefaultrunloopmode                                  beforedate:until];     } } 

if couldn't reproduce error, increase test item count 10000.

        (int = 1; < 10000; ++i) {         [items addobject:[nsstring stringwithformat:@"%d", i]];     } 

and comment nslog() command + u run unit test

here error message: otest(11105,0xb039f000) malloc: * error object 0xa0f8000: pointer being freed not allocated

otest(11209,0xb0115000) malloc: * error object 0x41dcc00: pointer being freed not allocated * set breakpoint in malloc_error_break debug

i cannot reproduce 'double free' error time