字符串缓存策略

    for (int i = 0; i < 1000; i++) {//100次不会闪退，次数少
        dispatch_async(dispatch_get_global_queue(0, 0), ^{
            people.name = [NSString stringWithFormat:@"asjkdhaksjdhkasd"];//__NSCFString
            NSLog(@"%@",[people.name class]);
        });
    }

//当字符串长的时候，用__NSCFString，是一个变量，会并发 set方法   并发release闪退
-(void)setName:(NSString *)name{
    if (_name != name) {
        [_name release];
        _name = [name retain];
    }
    return _name;
}

//当字符串短的时候用NSTaggedPointerString，是一个常量，指向同一个常量区，不会闪退
    for (int i = 0; i < 1000; i++) {
        dispatch_async(dispatch_get_global_queue(0, 0), ^{
            people.name = [NSString stringWithFormat:@"123456789"];//NSTaggedPointerString
            NSLog(@"%p",people.name);
            NSLog(@"%@",[people.name class]);
        });
    }