code: func clearDeadProjects(c context.Context, liveProjects stringset.Set) error {
  	var allProjects []*Project
  	projectQ := datastore.NewQuery("Project").KeysOnly(true)
  	if err := datastore.GetAll(c, projectQ, &allProjects); err != nil {
  		return err
  	}
  	return parallel.WorkPool(10, func(work chan<- func() error) {
  		for _, p := range allProjects {
  			p := p
  			if !liveProjects.Has(p.Name) {
  				work <- func() error {
  					logging.Warningf(c, "deleting project %s", p.Name)
  					return deleteProject(c, p.Name)
  				}
  			}
  		}
  	})
  }
docs: // clearDeadProjects calls deleteProject for all projects in the datastore
  // that are not in liveProjects.