Create soft link "_latest" in nni-experiments (#4476)

nni/experiment/launcher.py

@@ -110,8 +110,6 @@ def start_experiment(action, exp_id, config, port, debug, run_mode, url_prefix):
         _logger.info('Setting up...')
         rest.post(port, '/experiment', config.json(), url_prefix)
 
-        return proc
-
     except Exception as e:
         _logger.error('Create experiment failed')
         if proc is not None:
@@ -119,6 +117,16 @@ def start_experiment(action, exp_id, config, port, debug, run_mode, url_prefix):
                 proc.kill()
         raise e
 
+    link = Path(config.experiment_working_directory, '_latest')
+    try:
+        link.unlink(missing_ok=True)
+        link.symlink_to(exp_id, target_is_directory=True)
+    except Exception:
+        if sys.platform != 'win32':
+            _logger.warning(f'Failed to create link {link}')
+
+    return proc
+
 def _start_rest_server(nni_manager_args, run_mode) -> Tuple[int, Popen]:
     node_dir = Path(nni_node.__path__[0])
     node = str(node_dir / ('node.exe' if sys.platform == 'win32' else 'node'))