Dockerfile plays an important role in the Docker-based software development process, but many Dockerfile codes are infected with smells in practice. Understanding the occurrence of Dockerfile smells in open-source software can benefit the practice of Dockerfile and enhance project maintenance. In this paper, we perform an empirical study on a large dataset of 6,334 projects to help developers gain some insights into the occurrence of Dockerfile smells, including its coverage, distribution, cooccurrence, and correlation with project characteristics. Our results show that smells are very common in Dockerfile codes and there exists co-occurrence between different types of Dockerfile smells. Further, using linear regression analysis, when controlled for various variables, we statistically identify and quantify the relationships between Dockerfile smells occurrence and project characteristics. We also provide a rich resource of implications for software practitioners.

To encourage developers' volunteer contributions, modern programming question and answer (Q&A) sites like Stack Overflow (SO) employ gamified incentive mechanisms such as reputation and badges. Understanding developers' motivations in the presence of gamification and the relationship between their motivations and behavioral outcomes is crucial for community building and designing good incentive mechanisms. Grounded on self-determination theory, we conducted a survey with 938 developers who participate in SO to understand their participation motivations and incentive perceptions. By connecting the survey responses with the SO data, we quantitatively analyzed how the developers' motivations and satisfaction of needs relate to their effort and contribution quality. Our main findings are as follows: (1) despite the presence of gamified incentive mechanisms, developers are mainly motivated by intrinsic motivation to participate in SO; (2) developers who have strong motivations to gain gamification rewards are associated with higher intrinsic and integrated motivations, while developers with more development experiences are less motivated by the gamified incentives; (3) both extrinsic motivations (in terms of career prospects) and intrinsic motivations (regarding self-improvement and helping others) can motivate developers to make high-quantity and high-quality contributions; and (4) high-level satisfaction of needs for competency and autonomy has a positive effect on developers making high-quantity and high-quality contributions and addressing difficult problems. Based on these findings, we discuss implications for developer motivation and gamification in the crowdsourcing context and for the mechanism design of gamified crowdsourced platforms.