Fuzzing channel-based concurrency runtimes using types and effects

Quentin Stiévenart, Magnus Madsen

Research output: Contribution to book/anthology/report/proceedingArticle in proceedingsResearchpeer-review


Modern programming languages support concurrent programming based on channels and processes. Channels enable synchronous and asynchronous message-passing between independent light-weight processes making it easy to express common concurrency patterns. The implementation of channels and processes in compilers and language runtimes is a difficult task that relies heavily on traditional and error-prone low-level concurrency primitives, raising concerns about correctness and reliability. In this paper, we present an automatic program generation technique to test such programming language implementations. We define a type and effect system for programs that communicate over channels and where every execution is guaranteed to eventually terminate. We can generate and run such programs, and if a program fails to terminate, we have found a bug in the programming language implementation. We implement such an automatic program generator and apply it to Go, Kotlin, Crystal, and Flix. We find two new bugs in Flix, and reproduce two bugs; one in Crystal and one in Kotlin.

Original languageEnglish
Title of host publicationProceedings of the ACM on Programming Languages
Number of pages27
PublisherAssociation for Computing Machinery
Publication date13 Nov 2020
Publication statusPublished - 13 Nov 2020
SeriesACM SIGPLAN International Conference on Object-Oriented Programming, Systems, Languages and Applications


  • automatic test generation
  • channels and processes
  • effect systems


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