code: def main():
      ip_config = os.environ.get("DIST_DGL_TEST_IP_CONFIG")
      num_servers = int(os.environ.get("DIST_DGL_TEST_NUM_SERVERS"))
      if os.environ.get("DIST_DGL_TEST_ROLE", "server") == "server":
          server_id = int(os.environ.get("DIST_DGL_TEST_SERVER_ID"))
          num_clients = int(os.environ.get("DIST_DGL_TEST_NUM_CLIENTS"))
          keep_alive = "DIST_DGL_TEST_KEEP_ALIVE" in os.environ
          start_server(
              server_id, ip_config, num_servers, num_clients, keep_alive
          )
      else:
          group_id = int(os.environ.get("DIST_DGL_TEST_GROUP_ID", "0"))
          start_client(ip_config, num_servers, group_id)
  
file_path: dgl/tests/dist/python/rpc_basic.py
imports: import os
  import backend
  import dgl
  from numpy.testing import assert_array_equal
label_desc: Use image node_id 4 for calling a global function with example usage: main() without return types