[gRPC] Migrate raylet client implementation to grpc (#5120)

python/ray/__init__.py

@@ -5,6 +5,13 @@ from __future__ import print_function
 import os
 import sys
 
+# MUST import ray._raylet before pyarrow to initialize some global variables.
+# It seems the library related to memory allocation in pyarrow will destroy the
+# initialization of grpc if we import pyarrow at first.
+# NOTE(JoeyJiang): See https://github.com/ray-project/ray/issues/5219 for more
+# details.
+import ray._raylet
+
 if "pyarrow" in sys.modules:
     raise ImportError("Ray must be imported before pyarrow because Ray "
                       "requires a specific version of pyarrow (which is "