code: def testJoin(self):
      size = MPI.COMM_WORLD.Get_size()
      rank = MPI.COMM_WORLD.Get_rank()
      server = client = address = None
      host = socket.gethostname()
      addrinfo = socket.getaddrinfo(host, None, type=socket.SOCK_STREAM)
      addr_families = [info[0] for info in addrinfo]
      # if both INET and INET6 are available, don't assume the order
      # is the same on both server and client. Prefer INET if available.
      addr_family = None
      if socket.AF_INET in addr_families:
          addr_family = socket.AF_INET
      elif socket.AF_INET6 in addr_families:
          addr_family = socket.AF_INET6
      addr_family = MPI.COMM_WORLD.bcast(addr_family, root=0)
      supported = addr_family in addr_families
      supported = MPI.COMM_WORLD.allreduce(supported, op=MPI.LAND)
      if not supported:
          self.skipTest("socket-inet")
      # create server/client sockets
      if rank == 0:  # server
          server = socket.socket(addr_family, socket.SOCK_STREAM)
          server.bind((host, 0))
          server.listen(0)
      if rank == 1:  # client
          client = socket.socket(addr_family, socket.SOCK_STREAM)
      # communicate address
      if rank == 0:
          address = server.getsockname()
          MPI.COMM_WORLD.ssend(address, 1)
      if rank == 1:
          address = MPI.COMM_WORLD.recv(None, 0)
      MPI.COMM_WORLD.Barrier()
      # stablish client/server connection
      connected = False
      if rank == 0:  # server
          client = server.accept()[0]
          server.close()
      if rank == 1:  # client
          try:
              client.connect(address)
              connected = True
          except OSError:
              raise
      connected = MPI.COMM_WORLD.bcast(connected, root=1)
      # test Comm.Join()
      MPI.COMM_WORLD.Barrier()
      if client:
          fd = client.fileno()
          intercomm = MPI.Comm.Join(fd)
          client.close()
          if intercomm != MPI.COMM_NULL:
              self.assertEqual(intercomm.remote_size, 1)
              self.assertEqual(intercomm.size, 1)
              self.assertEqual(intercomm.rank, 0)
              if rank == 0:
                  message = TestDPM.message
                  root = MPI.ROOT
              else:
                  message = None
                  root = 0
              message = intercomm.bcast(message, root)
              if rank == 0:
                  self.assertIsNone(message)
              else:
                  self.assertEqual(message, TestDPM.message)
              intercomm.Free()
      MPI.COMM_WORLD.Barrier()
  
file_path: mpi4py/test/test_dynproc.py
imports: from mpi4py import MPI
  import mpiunittest
label_desc: Use image node_id 4 for calling the TestDPM obj's underlying member method code with example usage: obj.testJoin() without return types