prompt: We are currently solving the following issue within our repository. Here is the issue text:
  --- BEGIN ISSUE ---
  [PS-1]Add new RPC services definition in elasticdl.proto according to PS design
  [PS design](https://github.com/sql-machine-learning/elasticdl/blob/develop/docs/designs/ps_design.md#rpc-definition) adds some new RPC services.
  
  --- END ISSUE ---
  
  Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
  --- BEGIN FILES ---
  Path: `elasticdl/python/ps/servicer.py`
  Content:
  ```
  1 from google.protobuf import empty_pb2
  2 
  3 from elasticdl.proto import elasticdl_pb2_grpc
  4 
  5 
  6 class PserverServicer(elasticdl_pb2_grpc.PserverServicer):
  7     """PS service implementation"""
  8 
  9     def __init__(
  10         self,
  11         parameters,
  12         grads_to_wait,
  13         optimizer,
  14         lr_staleness_modulation=False,
  15         use_async=False,
  16     ):
  17         self._parameters = parameters
  18         self._grads_to_wait = grads_to_wait
  19         self._optimizer = optimizer
  20         self._lr_staleness_modulation = lr_staleness_modulation
  21         self._use_async = use_async
  22         self._version = 0
  23 
  24     def pull_variable(self, request, _):
  25         # TODO: implement this RPC service
  26         return empty_pb2.Empty()
  27 
  28     def pull_embedding_vector(self, request, _):
  29         # TODO: implement this RPC service
  30         return empty_pb2.Empty()
  31 
  32     def push_model(self, request, _):
  33         # TODO: implement this RPC service
  34         return empty_pb2.Empty()
  35 
  36     def push_gradient(self, request, _):
  37         # TODO: implement this RPC service
  38         return empty_pb2.Empty()
  39
  ```
  --- END FILES ---
  
  Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.
  
  Here is an example:
  
  ```diff
  diff --git a/examples/server_async.py b/examples/server_async.py
  --- a/examples/server_async.py
  +++ b/examples/server_async.py
  @@ -313,4 +313,4 @@
   
   
   if __name__ == "__main__":
  -    asyncio.run(run_async_server("."), debug=True)
  +    asyncio.run(run_async_server(), debug=True)
  diff --git a/examples/server_sync.py b/examples/server_sync.py
  --- a/examples/server_sync.py
  +++ b/examples/server_sync.py
  @@ -313,5 +313,5 @@
   
   
   if __name__ == "__main__":
  -    server = run_sync_server(".")
  +    server = run_sync_server()
       server.shutdown()
  
  ```
  
golden_diff: diff --git a/elasticdl/python/ps/servicer.py b/elasticdl/python/ps/servicer.py
  --- a/elasticdl/python/ps/servicer.py
  +++ b/elasticdl/python/ps/servicer.py
  @@ -1,6 +1,6 @@
   from google.protobuf import empty_pb2
   
  -from elasticdl.proto import elasticdl_pb2_grpc
  +from elasticdl.proto import elasticdl_pb2, elasticdl_pb2_grpc
   
   
   class PserverServicer(elasticdl_pb2_grpc.PserverServicer):
  @@ -23,11 +23,11 @@
   
       def pull_variable(self, request, _):
           # TODO: implement this RPC service
  -        return empty_pb2.Empty()
  +        return elasticdl_pb2.PullVariableResponse()
   
       def pull_embedding_vector(self, request, _):
           # TODO: implement this RPC service
  -        return empty_pb2.Empty()
  +        return elasticdl_pb2.Tensor()
   
       def push_model(self, request, _):
           # TODO: implement this RPC service
  @@ -35,4 +35,4 @@
   
       def push_gradient(self, request, _):
           # TODO: implement this RPC service
  -        return empty_pb2.Empty()
  +        return elasticdl_pb2.PushGradientResponse()
  
verification_info: {"golden_diff": "diff --git a/elasticdl/python/ps/servicer.py b/elasticdl/python/ps/servicer.py\n--- a/elasticdl/python/ps/servicer.py\n+++ b/elasticdl/python/ps/servicer.py\n@@ -1,6 +1,6 @@\n from google.protobuf import empty_pb2\n \n-from elasticdl.proto import elasticdl_pb2_grpc\n+from elasticdl.proto import elasticdl_pb2, elasticdl_pb2_grpc\n \n \n class PserverServicer(elasticdl_pb2_grpc.PserverServicer):\n@@ -23,11 +23,11 @@\n \n     def pull_variable(self, request, _):\n         # TODO: implement this RPC service\n-        return empty_pb2.Empty()\n+        return elasticdl_pb2.PullVariableResponse()\n \n     def pull_embedding_vector(self, request, _):\n         # TODO: implement this RPC service\n-        return empty_pb2.Empty()\n+        return elasticdl_pb2.Tensor()\n \n     def push_model(self, request, _):\n         # TODO: implement this RPC service\n@@ -35,4 +35,4 @@\n \n     def push_gradient(self, request, _):\n         # TODO: implement this RPC service\n-        return empty_pb2.Empty()\n+        return elasticdl_pb2.PushGradientResponse()\n", "issue": "[PS-1]Add new RPC services definition in elasticdl.proto according to PS design\n[PS design](https://github.com/sql-machine-learning/elasticdl/blob/develop/docs/designs/ps_design.md#rpc-definition) adds some new RPC services.\n", "before_files": [{"content": "from google.protobuf import empty_pb2\n\nfrom elasticdl.proto import elasticdl_pb2_grpc\n\n\nclass PserverServicer(elasticdl_pb2_grpc.PserverServicer):\n    \"\"\"PS service implementation\"\"\"\n\n    def __init__(\n        self,\n        parameters,\n        grads_to_wait,\n        optimizer,\n        lr_staleness_modulation=False,\n        use_async=False,\n    ):\n        self._parameters = parameters\n        self._grads_to_wait = grads_to_wait\n        self._optimizer = optimizer\n        self._lr_staleness_modulation = lr_staleness_modulation\n        self._use_async = use_async\n        self._version = 0\n\n    def pull_variable(self, request, _):\n        # TODO: implement this RPC service\n        return empty_pb2.Empty()\n\n    def pull_embedding_vector(self, request, _):\n        # TODO: implement this RPC service\n        return empty_pb2.Empty()\n\n    def push_model(self, request, _):\n        # TODO: implement this RPC service\n        return empty_pb2.Empty()\n\n    def push_gradient(self, request, _):\n        # TODO: implement this RPC service\n        return empty_pb2.Empty()\n", "path": "elasticdl/python/ps/servicer.py"}], "after_files": [{"content": "from google.protobuf import empty_pb2\n\nfrom elasticdl.proto import elasticdl_pb2, elasticdl_pb2_grpc\n\n\nclass PserverServicer(elasticdl_pb2_grpc.PserverServicer):\n    \"\"\"PS service implementation\"\"\"\n\n    def __init__(\n        self,\n        parameters,\n        grads_to_wait,\n        optimizer,\n        lr_staleness_modulation=False,\n        use_async=False,\n    ):\n        self._parameters = parameters\n        self._grads_to_wait = grads_to_wait\n        self._optimizer = optimizer\n        self._lr_staleness_modulation = lr_staleness_modulation\n        self._use_async = use_async\n        self._version = 0\n\n    def pull_variable(self, request, _):\n        # TODO: implement this RPC service\n        return elasticdl_pb2.PullVariableResponse()\n\n    def pull_embedding_vector(self, request, _):\n        # TODO: implement this RPC service\n        return elasticdl_pb2.Tensor()\n\n    def push_model(self, request, _):\n        # TODO: implement this RPC service\n        return empty_pb2.Empty()\n\n    def push_gradient(self, request, _):\n        # TODO: implement this RPC service\n        return elasticdl_pb2.PushGradientResponse()\n", "path": "elasticdl/python/ps/servicer.py"}]}