code: def sys_maxfd():
      
      maxfd = None
      try:
          maxfd = int(resource.getrlimit(resource.RLIMIT_NOFILE)[0])
          if maxfd == resource.RLIM_INFINITY:                                                     # pragma: no cover
              maxfd = None
      except: pass
      if maxfd is None:
          maxfd = sys_maxfd.fallback_maxfd
      return maxfd
docs: Returns the maximum file descriptor limit.  This is guaranteed to
      return a useful int value.