Monkey patching tornado to backport tornadoweb/tornado#1290

Should hopefully help with freezing/blocking issues upon first connect with the net on the Pi, more tests needed.

src/octoprint/server/__init__.py

@@ -58,6 +58,7 @@ import octoprint.filemanager.analysis
 import octoprint.slicing
 
 from . import util
+util.tornado.fix_ioloop_scheduling()
 
 
 UI_API_KEY = ''.join('%02X' % ord(z) for z in uuid.uuid4().bytes)
@@ -656,13 +657,7 @@ class Server():
 
 		## Tornado initialization starts here
 
-		try:
-			import monotime
-			import time
-			ioloop = IOLoop(time_func=time.monotonic)
-		except:
-			import time
-			ioloop = IOLoop(time_func=time.time)
+		ioloop = IOLoop()
 		ioloop.install()
 
 		self._router = SockJSRouter(self._createSocketConnection, "/sockjs")

src/octoprint/server/util/tornado.py

@@ -29,6 +29,36 @@ import tornado.util
 import octoprint.util
 
 
+#~~ Monkey patching
+
+
+def fix_ioloop_scheduling():
+	"""
+	This monkey patches tornado's :meth:`tornado.ioloop.PeriodicCallback._schedule_next` method so it no longer
+	blocks for long times on slow machines (RPi) when the system time happens to change by a large amount (e.g. due to
+	the first ever contact to an NTP server).
+
+	Patch by @nosyjoe on Github. See this PR against tornado: https://github.com/tornadoweb/tornado/pull/1290
+	"""
+
+	import math
+
+	# patched implementation taken from PR
+	def _schedule_next(self):
+		if self._running:
+			current_time = self.io_loop.time()
+
+			if self._next_timeout <= current_time:
+				callback_time_sec = self.callback_time / 1000.0
+				self._next_timeout += (math.floor((current_time - self._next_timeout) / callback_time_sec) + 1) * callback_time_sec
+
+			self._timeout = self.io_loop.add_timeout(self._next_timeout, self._run)
+
+	# replace original implementation with patched version
+	import tornado.ioloop
+	tornado.ioloop.PeriodicCallback._schedule_next = _schedule_next
+
+
 #~~ WSGI middleware