Reentrant Readers-Writers: A Case Study Combining Model Checking with Theorem Proving

The classic readers-writers problem has been extensively studied. This holds to a lesser degree for the reentrant version, where it is allowed to nest locking actions. Such nesting is useful when a library is created with various procedures that each start and end with a lock. Allowing nesting makes it possible for these procedures to call each other. We considered an existing widely used industrial implementation of the reentrant readers-writers problem. We modeled it using a model checker revealing a serious error: a possible deadlock situation. The model was improved and checked satisfactorily for a fixed number of processes. To achieve a correctness result for an arbitrary number of processes the model was converted to a theorem prover with which it was proven.