A computer readable medium contains a data structure, which, in some
embodiments, is an interface wrapper. The interface wrapper stores
information about the interface such as a first data field that contains
a reference to instrumentation, a second data field that contains data
which represents a reference to an interface of a software program, and a
third data field which contains data representing an identity of the unit
of software. When a client unit calls a member function of the interface,
the interface wrapper intercepts the call and invokes the
instrumentation.