Add worker queue for progress bar to prevent lost tqdm updates.

The worker queue runs in a background thread, so it's more likely to be
able to keep up with the other workers that are adding to the worker
queue.

bigquery/google/cloud/bigquery/table.py

@@ -22,6 +22,8 @@
 import datetime
 import json
 import operator
+import threading
+import time
 import warnings
 
 import six
@@ -69,6 +71,11 @@
 _MARKER = object()
 _PROGRESS_INTERVAL = 0.2  # Time between download status updates, in seconds.
 
+# Send multiple updates from the worker threads, so there are at least a few
+# waiting next time the prgrogess bar is updated.
+_PROGRESS_UPDATES_PER_INTERVAL = 3
+_PROGRESS_WORKER_INTERVAL = _PROGRESS_INTERVAL / _PROGRESS_UPDATES_PER_INTERVAL
+
 
 def _reference_getter(table):
     """A :class:`~google.cloud.bigquery.table.TableReference` pointing to
@@ -1275,7 +1282,7 @@ def __repr__(self):
         return "Row({}, {})".format(self._xxx_values, f2i)
 
 
-class _FakeQueue(object):
+class _NoopProgressBarQueue(object):
     """A fake Queue class that does nothing.
 
     This is used when there is no progress bar to send updates to.
@@ -1403,7 +1410,7 @@ def _to_dataframe_tabledata_list(self, dtypes, progress_bar=None):
         return pandas.concat(frames)
 
     def _to_dataframe_bqstorage_stream(
-        self, bqstorage_client, dtypes, columns, session, stream, progress_queue
+        self, bqstorage_client, dtypes, columns, session, stream, worker_queue
     ):
         position = bigquery_storage_v1beta1.types.StreamPosition(stream=stream)
         rowstream = bqstorage_client.read_rows(position).rows(session)
@@ -1415,7 +1422,7 @@ def _to_dataframe_bqstorage_stream(
             frames.append(page.to_dataframe(dtypes=dtypes))
 
             try:
-                progress_queue.put_nowait(page.num_items)
+                worker_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.
@@ -1430,6 +1437,30 @@ def _to_dataframe_bqstorage_stream(
         # the end using manually-parsed schema.
         return pandas.concat(frames)[columns]
 
+    def _process_worker_updates(self, worker_queue, progress_queue):
+        last_update_time = time.time()
+        current_update = 0
+
+        # Sum all updates in a contant loop.
+        while True:
+            try:
+                current_update += worker_queue.get(timeout=_PROGRESS_INTERVAL)
+
+                # Time to send to the progress bar queue?
+                current_time = time.time()
+                elapsed_time = current_time - last_update_time
+                if elapsed_time > _PROGRESS_WORKER_INTERVAL:
+                    progress_queue.put(current_update)
+                    last_update_time = current_time
+                    current_update = 0
+
+            except queue.Empty:
+                # Keep going, unless there probably aren't going to be any
+                # additional updates.
+                if self._to_dataframe_finished:
+                    progress_queue.put(current_update)
+                    return
+
     def _process_progress_updates(self, progress_queue, progress_bar):
         if progress_bar is None:
             return
@@ -1486,9 +1517,16 @@ def _to_dataframe_bqstorage(self, bqstorage_client, dtypes, progress_bar=None):
         self._to_dataframe_finished = False
 
         # Create a queue to track progress updates across threads.
-        progress_queue = _FakeQueue()
+        worker_queue = _NoopProgressBarQueue()
+        progress_queue = None
+        progress_thread = None
         if progress_bar is not None:
+            worker_queue = queue.Queue()
             progress_queue = queue.Queue()
+            progress_thread = threading.Thread(
+                target=self._process_worker_updates, args=(worker_queue, progress_queue)
+            )
+            progress_thread.start()
 
         def get_frames(pool):
             frames = []
@@ -1505,7 +1543,7 @@ def get_frames(pool):
                     columns,
                     session,
                     stream,
-                    progress_queue,
+                    worker_queue,
                 )
                 for stream in session.streams
             ]
@@ -1531,6 +1569,12 @@ def get_frames(pool):
                 # definition (enforced by the global interpreter lock).
                 self._to_dataframe_finished = True
 
+                # Shutdown all background threads, now that they should know to
+                # exit early.
+                pool.shutdown(wait=True)
+                if progress_thread is not None:
+                    progress_thread.join()
+
         # Update the progress bar one last time to close it.
         self._process_progress_updates(progress_queue, progress_bar)
         return pandas.concat(frames)

bigquery/tests/unit/test_table.py

@@ -1857,7 +1857,7 @@ def blocking_to_dataframe(*args, **kwargs):
         type(mock_rows).pages = mock.PropertyMock(return_value=mock_pages)
 
         # Test that full queue errors are ignored.
-        mock_queue = mock.create_autospec(mut._FakeQueue)
+        mock_queue = mock.create_autospec(mut._NoopProgressBarQueue)
         mock_queue().put_nowait.side_effect = queue.Full
 
         schema = [
@@ -1875,7 +1875,7 @@ def blocking_to_dataframe(*args, **kwargs):
             selected_fields=schema,
         )
 
-        with mock.patch.object(mut, "_FakeQueue", mock_queue), mock.patch(
+        with mock.patch.object(mut, "_NoopProgressBarQueue", mock_queue), mock.patch(
             "concurrent.futures.wait", wraps=concurrent.futures.wait
         ) as mock_wait:
             got = row_iterator.to_dataframe(bqstorage_client=bqstorage_client)
@@ -1953,8 +1953,11 @@ def test_to_dataframe_w_bqstorage_updates_progress_bar(self, tqdm_mock):
         # Make sure that this test updated the progress bar once per page from
         # each stream.
         total_pages = len(streams) * len(mock_pages)
-        self.assertEqual(tqdm_mock().update.call_count, total_pages)
-        tqdm_mock().update.assert_called_with(len(page_items))
+        expected_total_rows = total_pages * len(page_items)
+        actual_total_rows = sum(
+            [args[0] for args, kwargs in tqdm_mock().update.call_args_list]
+        )
+        self.assertEqual(actual_total_rows, expected_total_rows)
         tqdm_mock().close.assert_called_once()
 
     @unittest.skipIf(pandas is None, "Requires `pandas`")