SWU: restart asynchronously instead of synchronously

Otherwise we will block ourselves, waiting for the restart command to
complete which it only can when we are no longer there.

Should reduce restart times on update significantly.

Downside is that we no longer can wait for the return code of the
call. However, that should be caught by our UI handler timing out for
the restart and showing an error prompting the user to restart
manually.

src/octoprint/plugins/softwareupdate/__init__.py

@@ -868,7 +868,7 @@ class SoftwareUpdatePlugin(octoprint.plugin.BlueprintPlugin,
 
 		self._logger.info("Restarting...")
 		try:
-			util.execute(restart_command)
+			util.execute(restart_command, evaluate_returncode=False, async=True)
 		except exceptions.ScriptError as e:
 			self._logger.exception("Error while restarting via command {}".format(restart_command))
 			self._logger.warn("Restart stdout:\n{}".format(e.stdout))

src/octoprint/plugins/softwareupdate/util.py

@@ -9,12 +9,12 @@ __copyright__ = "Copyright (C) 2014 The OctoPrint Project - Released under terms
 from .exceptions import ScriptError
 
 
-def execute(command, cwd=None, evaluate_returncode=True):
+def execute(command, cwd=None, evaluate_returncode=True, async=False):
 	import sarge
 	p = None
 
 	try:
-		p = sarge.run(command, cwd=cwd, stdout=sarge.Capture(), stderr=sarge.Capture())
+		p = sarge.run(command, cwd=cwd, stdout=sarge.Capture(), stderr=sarge.Capture(), async=async)
 	except:
 		returncode = p.returncode if p is not None else None
 		stdout = p.stdout.text if p is not None and p.stdout is not None else ""

src/octoprint/server/__init__.py

@@ -550,7 +550,7 @@ class Server(object):
 			                             "on_shutdown",
 			                             sorting_context="ShutdownPlugin.on_shutdown")
 
-			# wait for shutdown even to be processed, but maximally for 15s
+			# wait for shutdown event to be processed, but maximally for 15s
 			event_timeout = 15.0
 			if eventManager.join(timeout=event_timeout):
 				self._logger.warn("Event loop was still busy processing after {}s, shutting down anyhow".format(event_timeout))
@@ -565,13 +565,16 @@ class Server(object):
 		def sigterm_handler(*args, **kwargs):
 			# will stop tornado on SIGTERM, making the program exit cleanly
 			def shutdown_tornado():
+				self._logger.debug("Shutting down tornado's IOLoop...")
 				ioloop.stop()
+			self._logger.debug("SIGTERM received...")
 			ioloop.add_callback_from_signal(shutdown_tornado)
 		signal.signal(signal.SIGTERM, sigterm_handler)
 
 		try:
 			# this is the main loop - as long as tornado is running, OctoPrint is running
 			ioloop.start()
+			self._logger.debug("Tornado's IOLoop stopped")
 		except (KeyboardInterrupt, SystemExit):
 			pass
 		except: