[rllib] Remove need to pass around registry (#2250)

* remove registry

* fix

* too many _

* fix

* cloudpickle

* Update registry.py

* yapf

* fix test

* fix kv check

python/ray/tune/util.py

@@ -2,12 +2,12 @@ from __future__ import absolute_import
 from __future__ import division
 from __future__ import print_function
 
-import base64
 from six.moves import queue
+import base64
+import numpy as np
 import threading
 
 import ray
-from ray.tune.registry import _to_pinnable, _from_pinnable
 
 _pinned_objects = []
 _fetch_requests = queue.Queue()
@@ -63,6 +63,22 @@ def _serve_get_pin_requests():
         pass
 
 
+def _to_pinnable(obj):
+    """Converts obj to a form that can be pinned in object store memory.
+
+    Currently only numpy arrays are pinned in memory, if you have a strong
+    reference to the array value.
+    """
+
+    return (obj, np.zeros(1))
+
+
+def _from_pinnable(obj):
+    """Retrieve from _to_pinnable format."""
+
+    return obj[0]
+
+
 if __name__ == '__main__':
     ray.init()
     X = pin_in_object_store("hello")