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

Question

I'm trying to practice the block and GCD/NSOperation, so I wrote this project Async-objc, but when I'm trying to test it with unit test, I always encountered 'double free' error, I thought there shouldn't be such error in ARC mode.
here is the 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;
for (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 are down %#", queue);
}];
[_mainQueue addOperation:blockOp];
}
this is the test code:
- (void)testEachWithBigData {
BOOL __block completed = false;
NSMutableArray *items = [NSMutableArray arrayWithCapacity:100];
for (int i = 1; i < 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 be 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;
for (NSNumber *num in result) {
STAssertEquals(index, [num integerValue], #"the value should be ordered");
index++;
}
completed = YES;
});
}
];
NSDate *until = [NSDate dateWithTimeIntervalSinceNow:10];
while (!completed && [until timeIntervalSinceNow] > 0) {
[[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode
beforeDate:until];
}
}
If you couldn't reproduce the error, increase the test item count to 10000.
for (int i = 1; i < 10000; ++i) {
[items addObject:[NSString stringWithFormat:#"%d", i]];
}
and comment the NSLog()
then Command + U to run the unit test
here is the error message:
otest(11105,0xb039f000) malloc: * error for object 0xa0f8000: pointer being freed was not allocated
otest(11209,0xb0115000) malloc: * error for object 0x41dcc00: pointer being freed was not allocated
* set a breakpoint in malloc_error_break to debug
I cannot reproduce the 'double free' error this time