[BEAM-8944] Change to use single thread in py sdk bundle progress rep…

…ort (apache#10387)

* [BEAM-8944] Change to single thread executor in python sdk bundle progress report

sdks/python/apache_beam/runners/worker/sdk_worker.py

@@ -29,6 +29,7 @@
 import threading
 import traceback
 from builtins import object
+from concurrent import futures
 from typing import TYPE_CHECKING
 from typing import Callable
 from typing import DefaultDict
@@ -104,6 +105,10 @@ def __init__(self,
         state_handler_factory=self._state_handler_factory,
         data_channel_factory=self._data_channel_factory,
         fns=self._fns)
+
+    # TODO(BEAM-8998) use common UnboundedThreadPoolExecutor to process bundle
+    #  progress once dataflow runner's excessive progress polling is removed.
+    self._report_progress_executor = futures.ThreadPoolExecutor(max_workers=1)
     self._worker_thread_pool = UnboundedThreadPoolExecutor()
     self._responses = queue.Queue()  # type: queue.Queue[beam_fn_api_pb2.InstructionResponse]
     _LOGGER.info('Initializing SDKHarness with unbounded number of workers.')
@@ -199,7 +204,7 @@ def task():
                 'Unknown process bundle instruction {}').format(
                     instruction_id)), request)
 
-    self._worker_thread_pool.submit(task)
+    self._report_progress_executor.submit(task)
 
   def _request_finalize_bundle(self, request):
     # type: (beam_fn_api_pb2.InstructionRequest) -> None