fix(mgb/mm_server): return -1 when create_mm_server failed

GitOrigin-RevId: 117bb80c06388d7b7c7ab71a787a1f03849a3871

python_module/megengine/distributed/util.py

@@ -63,9 +63,11 @@ def init_process_group(
     set_default_device(mgb.comp_node("gpu" + str(dev)))
 
     if rank == 0:
-        res = mgb.config.create_mm_server("0.0.0.0", master_port)
-        if res != master_port:
+        _master_port = mgb.config.create_mm_server("0.0.0.0", master_port)
+        if _master_port == -1:
             raise Exception("Failed to start server on port {}".format(master_port))
+    else:
+        assert master_port > 0, "master_port must be specified for non-zero rank"
 
 
 def is_distributed() -> bool:

python_module/src/cpp/mm_handler.cpp

@@ -214,11 +214,14 @@ public:
                 std::make_unique<ZmqRpc::ZmqRpcServer>("tcp://" + server_addr, port,
                                                        std::move(service));
         port = server->port();
+        if (port == -1) {
+            return -1;
+        }
+
         auto full_srv_addr = ssprintf("%s:%d", server_addr.c_str(), port);
         server->run();
         auto ins = m_addr2server.emplace(
                 full_srv_addr, ServerInfo{std::move(server)});
-        mgb_assert(ins.second);
 
         return port;
     }