code: @Override
      public void listenFor(final String libraryId, final Slot<? super Library> slot) {
          // Create a shared library listener
          new AbstractLibraryListener(libraryId, ownerID, Providers.bundleContext) {
              @Override
              void update() {
                  final String methodName = "update(): ";
                  // the shared library has arrived! 
                  Library library = Providers.getSharedLibrary(libraryId);
                  if (library == null) {
                      if (tc.isDebugEnabled())
                          Tr.debug(tc, methodName + "class loader " + ownerID + "received a notification from the shared library " + libraryId
                                       + " but the library could not be retrieved.");
                      return; // do nothing, not even deregister!
                  }
                  slot.fill(library);
                  deregister();
              }
          };
      }
docs: invoked by the blocking list when a synchronous fetch operation fails