Static Deadlock Detection for Asynchronous C# Programs

Asynchronous programming is a standard approach for designing responsive applications. Modern languages such as C# provide async/await primitives for the disciplined use of asynchrony. In spite of this, programs can deadlock because of incorrect use of blocking operations along with non-blocking (asynchronous) operations. While developers are aware of this problem, there is no automated technique to detect deadlocks in asynchronous programs. We present a novel representation of control flow and scheduling of asynchronous programs, called continuation scheduling graph and formulate necessary conditions for a deadlock to occur in a program. We design static analyses to construct continuation scheduling graphs of asynchronous C# programs and to identify deadlocks in them. We have implemented the static analyses in a tool called Dead Wait. Using Dead Wait, we found 43 previously unknown deadlocks in 11 asynchronous C# libraries. We reported the deadlocks to the library developers. They have confirmed and fixed 40 of them