Show pid when server starts.

frontends/ycdl_flask/ycdl_flask_dev.py

@@ -14,6 +14,7 @@ logging.getLogger().addHandler(handler)
 
 import argparse
 import gevent.pywsgi
+import os
 import sys
 
 from voussoirkit import pathclass
@@ -67,7 +68,7 @@ def ycdl_flask_launch(
     if refresh_rate is not None:
         backend.common.start_refresher_thread(refresh_rate)
 
-    message = f'Starting server on port {port}'
+    message = f'Starting server on port {port}, pid={os.getpid()}'
     if use_https:
         message += ' (https)'
     print(message)