Add a correct graceful shutdwon example for the asyncio API (#26622)

examples/python/helloworld/async_greeter_server.py

@@ -36,13 +36,7 @@ async def serve() -> None:
     server.add_insecure_port(listen_addr)
     logging.info("Starting server on %s", listen_addr)
     await server.start()
-    try:
-        await server.wait_for_termination()
-    except KeyboardInterrupt:
-        # Shuts down the server with 0 seconds of grace period. During the
-        # grace period, the server won't accept new connections and allow
-        # existing RPCs to continue within the grace period.
-        await server.stop(0)
+    await server.wait_for_termination()
 
 
 if __name__ == '__main__':

examples/python/helloworld/async_greeter_server_with_graceful_shutdown.py

@@ -0,0 +1,64 @@
+# Copyright 2021 The gRPC Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""The graceful shutdown example for the asyncio Greeter server."""
+
+import logging
+import asyncio
+import grpc
+
+import helloworld_pb2
+import helloworld_pb2_grpc
+
+# Coroutines to be invoked when the event loop is shutting down.
+_cleanup_coroutines = []
+
+
+class Greeter(helloworld_pb2_grpc.GreeterServicer):
+
+    async def SayHello(
+            self, request: helloworld_pb2.HelloRequest,
+            context: grpc.aio.ServicerContext) -> helloworld_pb2.HelloReply:
+        logging.info('Received request, sleeping for 4 seconds...')
+        await asyncio.sleep(4)
+        logging.info('Sleep completed, responding')
+        return helloworld_pb2.HelloReply(message='Hello, %s!' % request.name)
+
+
+async def serve() -> None:
+    server = grpc.aio.server()
+    helloworld_pb2_grpc.add_GreeterServicer_to_server(Greeter(), server)
+    listen_addr = '[::]:50051'
+    server.add_insecure_port(listen_addr)
+    logging.info("Starting server on %s", listen_addr)
+    await server.start()
+
+    async def server_graceful_shutdown():
+        logging.info("Starting graceful shutdown...")
+        # Shuts down the server with 0 seconds of grace period. During the
+        # grace period, the server won't accept new connections and allow
+        # existing RPCs to continue within the grace period.
+        await server.stop(5)
+
+    _cleanup_coroutines.append(server_graceful_shutdown())
+    await server.wait_for_termination()
+
+
+if __name__ == '__main__':
+    logging.basicConfig(level=logging.INFO)
+    loop = asyncio.get_event_loop()
+    try:
+        loop.run_until_complete(serve())
+    finally:
+        loop.run_until_complete(*_cleanup_coroutines)
+        loop.close()