Objective c 添加到enumerateObjectWithBlock内的集合（可变NSArray/NSDictionary）安全吗？

执行此代码安全吗？也就是说，同时添加到NSMutableArray或NSMutableDictionary是否安全

- (NSArray *)batchProcess:(NSArray *)inputList {
    NSMutableArray *outputList = [NSMutableArray arrayWithCapacity:inputList.count];

    [inputList enumerateObjectsWithOptions:NSEnumerationConcurrent 
               usingBlock:^(id thing, NSUInteger index, BOOL *stop){
        id processedThing = [self doProcessingOn:thing];

        [outputList addObject:processedThing];
    }];

    return outputList;
}

同时添加到NSMutableArray或NSMutableDictionary是否安全

- (NSArray *)batchProcess:(NSArray *)inputList {
    NSMutableArray *outputList = [NSMutableArray arrayWithCapacity:inputList.count];

    [inputList enumerateObjectsWithOptions:NSEnumerationConcurrent 
               usingBlock:^(id thing, NSUInteger index, BOOL *stop){
        id processedThing = [self doProcessingOn:thing];

        [outputList addObject:processedThing];
    }];

    return outputList;
}

除非您提供自己的同步机制，保证在任何给定时间只有一个线程使用它，它是不安全的。如果您以非线程安全的方式使用它，则应该预期未定义的行为