Fuzzing channel-based concurrency runtimes using types and effects

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