An automatic distributed partitioning system (ADPS) determines which unit exposes an interface. The ADPS detects a reference to an interface. For the interface, the ADPS assures that the unit that exposes the interface is identified. In some embodiments, a data structure such as a hash table associates interfaces with identified units. An interface wrapper for the interface stores the identity of the unit that exposes the interface, as well as information about the interface and a reference to instrumentation. When a client unit calls a member function of an interface, the interface wrapper intercepts the call and invokes the instrumentation. The instrumentation performs an operation such as profiling the application or classifying a unit. The ADPS detects when an interface is undocumented, and handles undocumented interfaces without invoking the full instrumentation capabilities of the ADPS.