googleapis · busunkim96 · Mar 19, 2020 · Mar 16, 2020 · Mar 19, 2020 · Mar 19, 2020
diff --git a/google/auth/transport/grpc.py b/google/auth/transport/grpc.py
@@ -51,14 +51,22 @@ class AuthMetadataPlugin(grpc.AuthMetadataPlugin):
            object used to refresh credentials as needed.
    """

+    # Python 2.7 has no default for max_workers.
+    # In Python >= 3.5, ThreadPoolExecutor defaults to the
+    # number of processors on the machine, multiplied by 5.
+    if six.PY2:  # pragma: NO COVER
+        max_workers = 5
+    else:
+        max_workers = None
+    _AUTH_THREAD_POOL = futures.ThreadPoolExecutor(max_workers=max_workers)
+
    def __init__(self, credentials, request):
        # pylint: disable=no-value-for-parameter
        # pylint doesn't realize that the super method takes no arguments
        # because this class is the same name as the superclass.
        super(AuthMetadataPlugin, self).__init__()
        self._credentials = credentials
        self._request = request
-        self._pool = futures.ThreadPoolExecutor(max_workers=1)

    def _get_authorization_headers(self, context):
        """Gets the authorization headers for a request.
@@ -89,12 +97,9 @@ def __call__(self, context, callback):
            callback (grpc.AuthMetadataPluginCallback): The callback that will
                be invoked to pass in the authorization metadata.
        """
-        future = self._pool.submit(self._get_authorization_headers, context)
+        future = self._AUTH_THREAD_POOL.submit(self._get_authorization_headers, context)
        future.add_done_callback(self._callback_wrapper(callback))

-    def __del__(self):
-        self._pool.shutdown(wait=False)
-

 def secure_authorized_channel(
    credentials,