Use Threading.current_thread

Issue [1] got resolved/addressed in eventlet in 0.23 version and currently
Openstack using eventlet's 0.24 version. So removing the workaround code.

[1]: eventlet/eventlet#172

fasteners/lock.py

@@ -119,29 +119,14 @@ class ReaderWriterLock(object):
     #: Reader owner type/string constant.
     READER = 'r'
 
-    @staticmethod
-    def _fetch_current_thread_functor():
-        # Until https://github.com/eventlet/eventlet/issues/172 is resolved
-        # or addressed we have to use complicated workaround to get a object
-        # that will not be recycled; the usage of threading.current_thread()
-        # doesn't appear to currently be monkey patched and therefore isn't
-        # reliable to use (and breaks badly when used as all threads share
-        # the same current_thread() object)...
-        if eventlet is not None and eventlet_patcher is not None:
-            if eventlet_patcher.is_monkey_patched('thread'):
-                return eventlet.getcurrent
-        return threading.current_thread
-
     def __init__(self,
                  condition_cls=threading.Condition,
                  current_thread_functor=None):
         self._writer = None
         self._pending_writers = collections.deque()
         self._readers = {}
         self._cond = condition_cls()
-        if current_thread_functor is None:
-            current_thread_functor = self._fetch_current_thread_functor()
-        self._current_thread = current_thread_functor
+        self._current_thread = threading.current_thread
 
     @property
     def has_pending_writers(self):