Add try-except for process.send_signal so it can work on Windows. (#3…

…1574)

The current subprocess_server uses process.send_signal to terminate the process. On Windows, this will raise a ValueError, as .terminate() should be used instead.

sdks/python/apache_beam/utils/subprocess_server.py

@@ -243,7 +243,11 @@ def _really_stop_process(process_and_endpoint):
       if process.poll() is not None:
         break
       logging.debug("Sending SIGINT to process")
-      process.send_signal(signal.SIGINT)
+      try:
+        process.send_signal(signal.SIGINT)
+      except ValueError:
+        # process.send_signal raises a ValueError on Windows.
+        process.terminate()
       time.sleep(1)
     if process.poll() is None:
       process.kill()