‘An Informal Proof on the Contradictory Role of Finalizers in a Garbage Collection Context’

Garbage collection in OOP languages provides facilities to hook code that is executed upon object finalization. Semantically, the point in time that finalizer code is executed is not determined by the application logic, but by the garbage collection system. This fact renders a potential mismatch, since application-specific code, i.e. the finalizer implementation, normally affecting program state and control flow, is called automatically at a point in time that is indifferent to the application semantics. Although an analogous situation is observed in event-based systems, since event processors are called-back asynchronously by the underlying system, there is a fundamental difference: while event generation is essentially nondeterministic, originated from external event sources, object destruction is a semantic action that is always decided by applications. In summary, the mismatch is that although applications decide if and when destruction occurs, the garbage collector is responsible to commit the relevant code. We prove that this mismatch is due to the contradictory presence of finalizers in a garbage collection context