fix pickling error with ThreadSynchronizer

Author: alimanfoo

docs/release.rst

@@ -9,7 +9,8 @@ Release notes
 Various minor improvements, including: ``Group`` objects support member access
 via dot notation (``__getattr__``); fixed metadata caching for ``Array.shape``
 property and derivatives; added ``Array.ndim`` property; fixed
-``Array.__array__`` method arguments; fixed bug in pickling ``Array`` state.
+``Array.__array__`` method arguments; fixed bug in pickling ``Array`` state;
+fixed bug in pickling ``ThreadSynchronizer``.
 
 .. _release_2.1.0:
 

zarr/sync.py

@@ -17,9 +17,9 @@ def __getitem__(self, item):
             return self.locks[item]
 
     def __getstate__(self):
-        return dict()
+        return True
 
-    def __setstate__(self, d):
+    def __setstate__(self, *args):
         # reinitialize from scratch
         self.__init__()