fix(client_utils): stop output reader thread on shutdown

bec_widgets/cli/client_utils.py

@@ -36,7 +36,9 @@ logger = bec_logger.logger
 IGNORE_WIDGETS = ["LaunchWindow"]
 PROCESS_TERMINATION_TIMEOUT = 10
 PROCESS_OUTPUT_THREAD_JOIN_TIMEOUT = 2
+PROCESS_OUTPUT_SELECT_TIMEOUT = 0.2
 GRACEFUL_SERVER_SHUTDOWN_TIMEOUT = 5
+OUTPUT_READER_STOP_EVENT_ATTR = "_bec_output_reader_stop_event"
 
 RegistryState: TypeAlias = dict[
     Literal["gui_id", "name", "widget_class", "config", "__rpc__", "container_proxy"],
@@ -57,14 +59,16 @@ def _filter_output(output: str) -> str:
     return output
 
 
-def _get_output(process, logger) -> None:
+def _get_output(process, logger, stop_event: threading.Event | None = None) -> None:
     log_func = {process.stdout: logger.debug, process.stderr: logger.info}
     stream_buffer = {process.stdout: [], process.stderr: []}
     try:
         os.set_blocking(process.stdout.fileno(), False)
         os.set_blocking(process.stderr.fileno(), False)
-        while process.poll() is None:
-            readylist, _, _ = select.select([process.stdout, process.stderr], [], [], 1)
+        while process.poll() is None and not (stop_event and stop_event.is_set()):
+            readylist, _, _ = select.select(
+                [process.stdout, process.stderr], [], [], PROCESS_OUTPUT_SELECT_TIMEOUT
+            )
             for stream in (process.stdout, process.stderr):
                 buf = stream_buffer[stream]
                 if stream in readylist:
@@ -180,6 +184,9 @@ def _join_process_output_thread(process, thread: threading.Thread | None, logger
     if not thread.is_alive():
         return
 
+    if stop_event := getattr(thread, OUTPUT_READER_STOP_EVENT_ATTR, None):
+        stop_event.set()
+
     for stream in (process.stdout, process.stderr):
         if stream is None:
             continue
@@ -187,7 +194,6 @@ def _join_process_output_thread(process, thread: threading.Thread | None, logger
             stream.close()
         except OSError as e:
             logger.error(f"Failed to close stream {str(e)}")
-            pass
     thread.join(timeout=PROCESS_OUTPUT_THREAD_JOIN_TIMEOUT)
     if thread.is_alive():
         logger.warning(
@@ -247,8 +253,14 @@ def _start_plot_process(
     if logger is None:
         process_output_processing_thread = None
     else:
+        process_output_stop_event = threading.Event()
         process_output_processing_thread = threading.Thread(
-            target=_get_output, args=(process, logger)
+            target=_get_output, args=(process, logger, process_output_stop_event)
+        )
+        setattr(
+            process_output_processing_thread,
+            OUTPUT_READER_STOP_EVENT_ATTR,
+            process_output_stop_event,
         )
         process_output_processing_thread.start()
     return process, process_output_processing_thread

tests/end-2-end/test_rpc_widgets_e2e.py

@@ -69,7 +69,7 @@ def create_widget(
     return widget
 
 
-@pytest.mark.timeout(100)
+@pytest.mark.timeout(20)
 def test_available_widgets(qtbot, connected_client_gui_obj):
     """This test checks that all widgets that are available via gui.available_widgets can be created and removed."""
     gui = connected_client_gui_obj

tests/unit_tests/test_client_utils.py

@@ -6,7 +6,12 @@ from unittest import mock
 import pytest
 
 from bec_widgets.cli.client import BECDockArea
-from bec_widgets.cli.client_utils import BECGuiClient, _start_plot_process
+from bec_widgets.cli.client_utils import (
+    OUTPUT_READER_STOP_EVENT_ATTR,
+    BECGuiClient,
+    _join_process_output_thread,
+    _start_plot_process,
+)
 from bec_widgets.cli.rpc.rpc_base import RPCBase, RPCResponseTimeoutError, rpc_timeout
 
 
@@ -346,3 +351,21 @@ def test_client_utils_kill_server_kills_process_group_after_timeout():
         text=True,
         timeout=2,
     )
+
+
+def test_join_process_output_thread_signals_reader_before_closing_streams():
+    process = mock.MagicMock(pid=123, args=["bec-gui-server"])
+    process.stdout = mock.MagicMock()
+    process.stderr = mock.MagicMock()
+    thread = mock.MagicMock()
+    stop_event = mock.MagicMock()
+    setattr(thread, OUTPUT_READER_STOP_EVENT_ATTR, stop_event)
+    thread.is_alive.side_effect = [True, False]
+    logger = mock.MagicMock()
+
+    _join_process_output_thread(process, thread, logger)
+
+    assert thread.join.call_args_list == [mock.call(timeout=2), mock.call(timeout=2)]
+    stop_event.set.assert_called_once_with()
+    process.stdout.close.assert_called_once_with()
+    process.stderr.close.assert_called_once_with()