Pub/Sub: update publish with batch settings sample (#3137)

* non-blocking publish

* remove unused lib

* lint

* add defaults

pubsub/cloud-client/publisher.py

@@ -180,20 +180,28 @@ def publish_messages_with_batch_settings(project_id, topic_name):
     # TODO project_id = "Your Google Cloud Project ID"
     # TODO topic_name = "Your Pub/Sub topic name"
 
-    # Configure the batch to publish as soon as there is one kilobyte
-    # of data or one second has passed.
+    # Configure the batch to publish as soon as there is ten messages,
+    # one kilobyte of data, or one second has passed.
     batch_settings = pubsub_v1.types.BatchSettings(
-        max_bytes=1024, max_latency=1  # One kilobyte  # One second
+        max_messages=10,  # default 100
+        max_bytes=1024,  # default 1 MB
+        max_latency=1,  # default 10 ms
     )
     publisher = pubsub_v1.PublisherClient(batch_settings)
     topic_path = publisher.topic_path(project_id, topic_name)
 
+    # Resolve the publish future in a separate thread.
+    def callback(future):
+        message_id = future.result()
+        print(message_id)
+
     for n in range(1, 10):
         data = u"Message number {}".format(n)
         # Data must be a bytestring
         data = data.encode("utf-8")
         future = publisher.publish(topic_path, data=data)
-        print(future.result())
+        # Non-blocking. Allow the publisher client to batch multiple messages.
+        future.add_done_callback(callback)
 
     print("Published messages with batch settings.")
     # [END pubsub_publisher_batch_settings]