perf(recipe): Give TreeCache standalone queue

This commit lets TreeCache do not use queue of connection routine any more.

kazoo/recipe/cache.py

@@ -36,6 +36,8 @@ class TreeCache(object):
     STATE_STARTED = 1
     STATE_CLOSED = 2
 
+    _STOP = object()
+
     def __init__(self, client, path):
         self._client = client
         self._root = TreeNode.make_root(self, path)
@@ -44,6 +46,8 @@ def __init__(self, client, path):
         self._is_initialized = False
         self._error_listeners = []
         self._event_listeners = []
+        self._task_queue = client.handler.queue_impl()
+        self._task_thread = None
 
     def start(self):
         """Starts the cache.
@@ -66,6 +70,7 @@ def start(self):
         else:
             raise KazooException('already started')
 
+        self._task_thread = self._client.handler.spawn(self._do_background)
         self._client.add_listener(self._session_watcher)
         self._client.ensure_path(self._root._path)
 
@@ -87,6 +92,7 @@ def close(self):
         """
         if self._state == self.STATE_STARTED:
             self._state = self.STATE_CLOSED
+            self._task_queue.put(self._STOP)
             self._client.remove_listener(self._session_watcher)
             with handle_exception(self._error_listeners):
                 self._root.on_deleted()
@@ -168,7 +174,16 @@ def _do_publish_event(self, event):
                 listener(event)
 
     def _in_background(self, func, *args, **kwargs):
-        self._client.handler.callback_queue.put(lambda: func(*args, **kwargs))
+        self._task_queue.put((func, args, kwargs))
+
+    def _do_background(self):
+        while True:
+            with handle_exception(self._error_listeners):
+                cb = self._task_queue.get()
+                if cb is self._STOP:
+                    break
+                func, args, kwargs = cb
+                func(*args, **kwargs)
 
     def _session_watcher(self, state):
         if state == KazooState.SUSPENDED: