WIP: Add progress bar when BQ Storage API is used.

bigquery/google/cloud/bigquery/table.py

@@ -21,6 +21,7 @@
 import datetime
 import json
 import operator
+import queue
 import warnings
 
 import six
@@ -1255,6 +1256,16 @@ def __repr__(self):
         return "Row({}, {})".format(self._xxx_values, f2i)
 
 
+class _FakeQueue(object):
+    """A fake Queue class that does nothing.
+
+    This is used when there is no progress bar to send updates to.
+    """
+
+    def put_nowait(self, item):
+        """Don't actually do anything with the item."""
+
+
 class RowIterator(HTTPIterator):
     """A class for iterating through HTTP/JSON API row list responses.
 
@@ -1368,7 +1379,7 @@ def _to_dataframe_tabledata_list(self, dtypes, progress_bar=None):
 
         return pandas.concat(frames)
 
-    def _to_dataframe_bqstorage(self, bqstorage_client, dtypes):
+    def _to_dataframe_bqstorage(self, bqstorage_client, dtypes, progress_bar=None):
         """Use (faster, but billable) BQ Storage API to construct DataFrame."""
         import concurrent.futures
         from google.cloud import bigquery_storage_v1beta1
@@ -1407,6 +1418,11 @@ def _to_dataframe_bqstorage(self, bqstorage_client, dtypes):
         # https://stackoverflow.com/a/29237343/101923
         finished = False
 
+        # Create a queue to track progress updates across threads.
+        progress_queue = _FakeQueue()
+        if progress_bar is not None:
+            progress_queue = queue.Queue()
+
         def get_dataframe(stream):
             position = bigquery_storage_v1beta1.types.StreamPosition(stream=stream)
             rowstream = bqstorage_client.read_rows(position).rows(session)
@@ -1417,6 +1433,13 @@ def get_dataframe(stream):
                     return
                 frames.append(page.to_dataframe(dtypes=dtypes))
 
+                try:
+                    progress_queue.put_nowait(page.num_items)
+                except queue.Full:
+                    # It's okay if we miss a few progress updates. Don't slow
+                    # down parsing for that.
+                    pass
+
             # Avoid errors on unlucky streams with no blocks. pandas.concat
             # will fail on an empty list.
             if not frames:
@@ -1441,9 +1464,31 @@ def get_frames(pool):
                     not_done, timeout=_PROGRESS_INTERVAL
                 )
                 frames.extend([future.result() for future in done])
+
+                # The progress bar needs to update on the main thread to avoid
+                # contention over stdout / stderr.
+                if progress_bar is not None:
+                    update_progress_bar()
+
             return frames
 
+        def update_progress_bar():
+            if finished:
+                progress_bar.close()
+                return
+
+            # Output all updates since the last interval.
+            while True:
+                try:
+                    next_update = progress_queue.get_nowait()
+                    progress_bar.update(next_update)
+                except queue.Empty:
+                    return
+
         with concurrent.futures.ThreadPoolExecutor() as pool:
+            if progress_bar is not None:
+                pool.submit(update_progress_bar)
+
             try:
                 frames = get_frames(pool)
             finally:
@@ -1549,7 +1594,7 @@ def to_dataframe(self, bqstorage_client=None, dtypes=None, progress_bar_type=Non
 
         if bqstorage_client is not None:
             try:
-                return self._to_dataframe_bqstorage(bqstorage_client, dtypes)
+                return self._to_dataframe_bqstorage(bqstorage_client, dtypes, progress_bar=progress_bar)
             except google.api_core.exceptions.Forbidden:
                 # Don't hide errors such as insufficient permissions to create
                 # a read session, or the API is not enabled. Both of those are