Allow manually tuning the max. number of threads

#160

buildgrid/_app/commands/cmd_server.py

@@ -119,6 +119,14 @@ def _create_server_from_config(configuration):
             click.echo("Error: Configuration, {}.".format(e), err=True)
             sys.exit(-1)
 
+    if 'thread-pool-size' in configuration:
+        try:
+            kargs['max_workers'] = int(configuration['thread-pool-size'])
+
+        except ValueError as e:
+            click.echo("Error: Configuration, {}.".format(e), err=True)
+            sys.exit(-1)
+
     server = BuildGridServer(**kargs)
 
     try:

buildgrid/_app/settings/reference.yml

@@ -136,3 +136,7 @@ monitoring:
   #  binary  - Protobuf binary format.
   #  json    - JSON format.
   serialization-format: binary
+
+##
+# Maximum number of gRPC threads.
+thread-pool-size: 20

buildgrid/server/instance.py

@@ -91,6 +91,8 @@ class BuildGridServer:
         self.__grpc_server = grpc.server(self.__grpc_executor,
                                          options=(('grpc.so_reuseport', 0),))
 
+        self.__logger.debug("Setting up gRPC server with thread-limit=[%s]", max_workers)
+
         self.__main_loop = asyncio.get_event_loop()
 
         self.__monitoring_bus = None

data/config/controller.conf

@@ -38,3 +38,5 @@ instances:
       - !execution
         storage: *data-store
         action-cache: *build-cache
+
+thread-pool-size: 200