For( ; ; ) 、 For( in )、 enumerateObjectsUsingBlock  三者的执行效率依次提高！

详见：http://www.cnblogs.com/skyming/p/3977075.html

 NSArray *arr = [NSArray arrayWithObjects:@"温志平", @"阿大志平", @"温水豆腐平", @"温志时代", @"温问问问平", @"谁的粉丝", @"是对的事", @"肉肉吧", @"以后拒绝", @"3好纠结", @"对的", nil];

    [arr enumerateObjectsWithOptions:NSEnumerationConcurrent usingBlock:^(id  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {

        NSLog(@"index = %lu,  %@", idx, [arr objectAtIndex:idx]);

    }];

    

    

    [arr enumerateObjectsWithOptions:NSEnumerationReverse usingBlock:^(id  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {

        NSLog(@"index = %lu,  %@", idx, [arr objectAtIndex:idx]);

    }];

输出：

2016-03-28 11:40:52.932 AblumDemo[29184:910291] index = 0,  温志平

2016-03-28 11:40:52.933 AblumDemo[29184:910291] index = 4,  温问问问平

2016-03-28 11:40:52.932 AblumDemo[29184:910323] index = 1,  阿大志平

2016-03-28 11:40:52.933 AblumDemo[29184:910291] index = 5,  谁的粉丝

2016-03-28 11:40:52.933 AblumDemo[29184:910291] index = 6,  是对的事

2016-03-28 11:40:52.932 AblumDemo[29184:910324] index = 2,  温水豆腐平

2016-03-28 11:40:52.934 AblumDemo[29184:910291] index = 8,  以后拒绝

2016-03-28 11:40:52.932 AblumDemo[29184:910325] index = 3,  温志时代

2016-03-28 11:40:52.934 AblumDemo[29184:910323] index = 7,  肉肉吧

2016-03-28 11:40:52.934 AblumDemo[29184:910291] index = 10,  对的

2016-03-28 11:40:52.934 AblumDemo[29184:910324] index = 9,  3好纠结

2016-03-28 11:40:52.934 AblumDemo[29184:910291] index = 10,  对的

2016-03-28 11:40:52.934 AblumDemo[29184:910291] index = 9,  3好纠结

2016-03-28 11:40:52.934 AblumDemo[29184:910291] index = 8,  以后拒绝

2016-03-28 11:40:52.934 AblumDemo[29184:910291] index = 7,  肉肉吧

2016-03-28 11:40:52.934 AblumDemo[29184:910291] index = 6,  是对的事

2016-03-28 11:40:52.944 AblumDemo[29184:910291] index = 5,  谁的粉丝

2016-03-28 11:40:52.944 AblumDemo[29184:910291] index = 4,  温问问问平

2016-03-28 11:40:52.944 AblumDemo[29184:910291] index = 3,  温志时代

2016-03-28 11:40:52.945 AblumDemo[29184:910291] index = 2,  温水豆腐平

2016-03-28 11:40:52.945 AblumDemo[29184:910291] index = 1,  阿大志平

2016-03-28 11:40:52.945 AblumDemo[29184:910291] index = 0,  温志平

结论：enumerateObjectsUsingBlock 是一个并发的执行，这种情况仅限于NSEnumerationConcurrent倒序输出的情况！