Deterministic MultiThreading (DMT) systems eliminate nondeterminism from the dynamic executions of multithreaded programs. They can greatly simplify multithreaded programming and ease the deployment of systems that rely on replication. We first categorize and compare existing DMT system designs along three axes, incorporating the most recent advances in DMT systems. From our study, we conclude that stable synchronization determinism is the most cost-effective design, and it is thus the focus of our work.

Server-side web applications are vulnerable to request races. While some previous studies of real-world request races exist, they primarily focus on the root cause of these bugs. To better combat request races in server-side web applications, we need a deep understanding of their characteristics. In this paper, we provide a complementary focus on race effects and fixes with an enlarged set of request races from web applications developed with Object-Relational Mapping (ORM) frameworks. We revisit characterization questions used in previous studies on newly included request races, distinguish the external and internal effects of request races, and relate request-race fixes with concurrency control mechanisms in languages and frameworks for developing server-side web applications.

Deadlocks in database-backed web applications could involve different numbers of HTTP requests, and they could be caused by locks explicitly requested in application code or implicitly requested by databases during query execution. To help developers understand these deadlocks and guide the design of tools for combating these deadlocks, we conduct a characteristic study with 49 deadlocks collected from real-world web applications developed following different programming paradigms. We provide categorization results based on HTTP request numbers and resource types, with a special focus on cat-egorizing deadlocks on database locks. We expect our results to be useful for application developers to understand web-application deadlocks and for tool researchers to design comprehensive support for combating web-application deadlocks.

Modern web sites often run web applications on the server to handle HTTP requests from users and generate dynamic responses. Due to their concurrent nature, web applications are vulnerable to server-side request races. The problem becomes more severe with the ever-increasing popularity of web applications.

Database-backed web applications are prone to performance bugs related to database accesses. While much work has been conducted on database-access antipatterns with some recent work focusing on performance impact, there still lacks a comprehensive view of database-access performance antipatterns in database-backed web applications. To date, no existing work systematically reports known antipatterns in the literature, and no existing work has studied database-access performance bugs in major types of web applications that access databases differently.To address this issue, we first summarize all known database-access performance antipatterns found through our literature survey, and we report all of them in this paper. We further collect database-access performance bugs from web applications that access databases through language-provided SQL interfaces, which have been largely ignored by recent work, to check how extensively the known antipatterns can cover these bugs. For bugs not covered by the known antipatterns, we extract new database-access performance antipatterns based on real-world performance bugs from such web applications. Our study in total reports 24 known and 10 new database-access performance antipatterns. Our results can guide future work to develop effective tool support for different types of web applications.

Ad hoc synchronizations are pervasive in multi-threaded programs. Due to their diversity and complexity, understanding the enforced synchronization relationships of ad hoc synchronizations is challenging but crucial to multi-threaded program development and maintenance. Existing techniques can partially detect primitive ad hoc synchronizations, but they cannot recognize complete implementations or infer the enforced synchronization relationships. In this paper, we propose a framework to automatically identify complex ad hoc synchronizations in full and infer their synchronization relationships for barriers. We instantiate the framework with a tool called BARRIERFINDER, which features various techniques, including program slicing and bounded symbolic execution, to efficiently explore interleaving space of ad hoc synchronizations within multi-threaded programs for their traces. BARRIERFINDER then uses these traces to recognize ad hoc barriers. Our evaluation shows that BARRIERFINDER is both effective and efficient in recognizing ad hoc barriers automatically.

A common task for all deterministic multithreading (DMT) systems is to enforce synchronization determinism. However, synchronization determinism has not been the focus of existing DMT research. Instead, most DMT systems focused on how to order data races remained after synchronization determinism is enforced. Consequently, existing scheduling policies for synchronization determinism all have limitations. They may either require performance annotations to achieve good performance or fail to provide schedule stability.