Cooperari: A Tool for Cooperative Testing of Multithreaded Java Programs

Bugs in multithreaded application can be elusive. They are often hard to trace and replicate, given the usual non-determinism and ir-reproducibility of scheduling decisions at runtime. We present Co-operari, a tool for deterministic testing of multithreaded Java code based on cooperative execution. In a cooperative execution, threads voluntarily suspend (yield) at interference points (e.g., lock acquisi-tion), and code between two consecutive yield points of each thread always executes serially as a transaction. A cooperative scheduler takes over control at yield points and deterministically selects the next thread to run. An application test runs multiple times, until it either fails or the state-space of schedules is deemed as covered by a configurable policy that is responsible for the scheduling decisions. Beyond failed assertions in software tests, deadlocks and races are also detected as soon as they are exposed in the cooperative exe-cution. Cooperari effectively finds, characterizes, and determinis-tically reproduces bugs that are not detected under unconstrained preemptive semantics, as illustrated by standard benchmark exam-ples