Deadlock and Starvation Free Reentrant Readers-Writers

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 each starting and ending with a lock operation. 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. Staying close to the original code, we modeled and analyzed it using a model checker resulting in the detection of 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 specification that was proven with a theorem prover. Furthermore, we studied starvation. Using model checking we found a starvation problem. We have fixed the problem and checked the solution. Combining model checking with theorem proving appeared to be very effective in reducing the time of the verification process.