Windows doesn't have a USR1 signal.

flamenco_worker/cli.py

@@ -96,6 +96,9 @@ def main():
     import signal
     signal.signal(signal.SIGTERM, shutdown)
     signal.signal(signal.SIGINT, shutdown)
+
+    if hasattr(signal, 'SIGUSR1'):
+        # Windows doesn't have a USR1 signal.
         signal.signal(signal.SIGUSR1, asyncio_report_tasks)
 
     # Start asynchronous tasks.