code: def group_callback(self, iocb):
          
          if _debug: IOGroup._debug("group_callback %r", iocb)
  
          # check all the members
          for iocb in self.ioMembers:
              if not iocb.ioComplete.isSet():
                  if _debug: IOGroup._debug("    - waiting for child: %r", iocb)
                  break
          else:
              if _debug: IOGroup._debug("    - all children complete")
              # everything complete
              self.ioState = COMPLETED
              self.trigger()
docs: Callback when a child iocb completes.