The following structure maintains interp callback traces. The traces are normally registered during server startup and invoked later for virutal server interps at specific points in the lifetime of the interp. Initialization callbacks (create, alloc, getconn) are called in FIFO order while finalization callbacks (freeconn, dealloc, delete) are called in LIFO order. In addition, script callbacks are invoked after non-script callbacks. A common trace would be an "create" trace to add commands in a loadable C module, e.g., the "ns_accesslog" command in nslog.
