From 571a564f5111c13c812bbfce397c5793131c8da4 Mon Sep 17 00:00:00 2001
From: Richard Belleville <rbellevi@google.com>
Date: Tue, 24 Mar 2020 14:23:25 -0700
Subject: [PATCH] Add type annotations and comments

---
 examples/python/xds/README.md |  2 +-
 examples/python/xds/server.py | 24 ++++++++++++++++++++----
 2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/examples/python/xds/README.md b/examples/python/xds/README.md
index 5dacfc4371e..51bfe715583 100644
--- a/examples/python/xds/README.md
+++ b/examples/python/xds/README.md
@@ -22,7 +22,7 @@ cd grpc/examples/python/xds
 ```sh
 virtualenv venv -p python3
 source venv/bin/activate
-pip install grpcio protobuf
+pip install grpcio protobuf grpcio-reflection grpcio-health-checking
 python server.py
 ```
 
diff --git a/examples/python/xds/server.py b/examples/python/xds/server.py
index 2b459eb39f3..3cff567667f 100644
--- a/examples/python/xds/server.py
+++ b/examples/python/xds/server.py
@@ -16,6 +16,7 @@
 from concurrent import futures
 import argparse
 import logging
+import multiprocessing
 import socket
 
 import grpc
@@ -33,31 +34,46 @@ _DESCRIPTION = "A general purpose dummy server."
 
 class Greeter(helloworld_pb2_grpc.GreeterServicer):
 
-    def __init__(self, hostname):
+    def __init__(self, hostname: str):
         self._hostname = hostname if hostname else socket.gethostname()
 
-    def SayHello(self, request, context):
+    def SayHello(self, request: helloworld_pb2.HelloRequest,
+                 context: grpc.ServicerContext) -> helloworld_pb2.HelloReply:
         return helloworld_pb2.HelloReply(
             message=f"Hello {request.name} from {self._hostname}!")
 
 
 def serve(port, hostname):
-    server = grpc.server(futures.ThreadPoolExecutor(max_workers=10))
+    server = grpc.server(
+        futures.ThreadPoolExecutor(max_workers=multiprocessing.cpu_count()))
+
+    # Add the application servicer to the server.
     helloworld_pb2_grpc.add_GreeterServicer_to_server(Greeter(hostname), server)
+
+    # Create a health check servicer. We use the non-blocking implementation
+    # to avoid thread starvation.
     health_servicer = health.HealthServicer(
         experimental_non_blocking=True,
-        experimental_thread_pool=futures.ThreadPoolExecutor(max_workers=4))
+        experimental_thread_pool=futures.ThreadPoolExecutor(max_workers=1))
     health_pb2_grpc.add_HealthServicer_to_server(health_servicer, server)
+
+    # Create a tuple of all of the services we want to export via reflection.
     services = tuple(
         service.full_name
         for service in helloworld_pb2.DESCRIPTOR.services_by_name.values()) + (
             reflection.SERVICE_NAME, health.SERVICE_NAME)
+
+    # Add the reflection service to the server.
     reflection.enable_server_reflection(services, server)
     server.add_insecure_port(f"[::]:{port}")
     server.start()
+
+    # Mark all services as healthy.
     overall_server_health = ""
     for service in services + (overall_server_health,):
         health_servicer.set(service, health_pb2.HealthCheckResponse.SERVING)
+
+    # Park the main application thread.
     server.wait_for_termination()