Move TypedQueue to octoprint.util & make generic

put and get are now overwritten to create t-tuple out of provided item
and item_type on put, and to only return item on get.

_put and _get extract item_type and use that for managing the
lookup set.

src/octoprint/util/__init__.py

@@ -18,6 +18,7 @@ import threading
 from functools import wraps
 import warnings
 import contextlib
+import Queue as queue
 
 logger = logging.getLogger(__name__)
 
@@ -884,3 +885,43 @@ class InvariantContainer(object):
 
 	def __iter__(self):
 		return self._data.__iter__()
+
+
+class TypedQueue(queue.Queue):
+
+	def __init__(self, maxsize=0):
+		queue.Queue.__init__(self, maxsize=maxsize)
+		self._lookup = set()
+
+	def put(self, item, item_type=None, *args, **kwargs):
+		queue.Queue.put(self, (item, item_type), *args, **kwargs)
+
+	def get(self, *args, **kwargs):
+		item, _ = queue.Queue.get(self, *args, **kwargs)
+		return item
+
+	def _put(self, item):
+		_, item_type = item
+		if item_type is not None:
+			if item_type in self._lookup:
+				raise TypeAlreadyInQueue(item_type, "Type {} is already in queue".format(item_type))
+			else:
+				self._lookup.add(item_type)
+
+		queue.Queue._put(self, item)
+
+	def _get(self):
+		item = queue.Queue._get(self)
+		_, item_type = item
+
+		if item_type is not None:
+			self._lookup.discard(item_type)
+
+		return item
+
+
+class TypeAlreadyInQueue(Exception):
+	def __init__(self, t, *args, **kwargs):
+		Exception.__init__(self, *args, **kwargs)
+		self.type = t
+