[app] Fix thread safety issues when stopping scan

Unlike previously, we're now changing the scanner object in the ScanWindow from the scan thread, which we need to synchronize with the main UI thread.

Note that some properties are still accessed without locks, but these are only informational (e.g. the name of the video being processed).

Author: Breakthrough

dvr_scan/app/scan_window.py

@@ -51,12 +51,9 @@ def __init__(
         self._total_videos = len(settings)
         self._multi_video_mode = self._total_videos > 1
 
-        # Initialize scanner for the first video
-        self._scanner = init_scanner(self._settings_list[0])
-        self._scanner.set_callbacks(
-            scan_started=self._on_scan_started,
-            processed_frame=self._on_processed_frame,
-        )
+        # Scanner is created in _do_scan for each video
+        self._scanner = None
+        self._scanner_lock = threading.Lock()
 
         # Determine if we should open folder on completion
         first_settings = self._settings_list[0]
@@ -102,8 +99,8 @@ def __init__(
             current_row += 1
 
             # Current video name label
-            video_name = Path(self._settings_list[0].get("input")[0]).name
-            self._current_video_label = tk.Label(self._root, text=f"Current: {video_name}")
+            self._current_video_name = Path(self._settings_list[0].get("input")[0]).name
+            self._current_video_label = tk.Label(self._root, text=f"{self._current_video_name}")
             self._current_video_label.grid(row=current_row, column=0, columnspan=2, sticky=tk.NSEW)
             current_row += 1
         else:
@@ -192,8 +189,7 @@ def _update(self):
                 logger.critical(f"error during scan:\n{formatted_exception}")
                 messagebox.showerror(
                     "Scan Error",
-                    "Error during scanning. See log messages for more info."
-                    f"\nSummary: {self._scan_exception}",
+                    f"Error during scan: {self._scan_exception}\n\nSee log messages for more info.",
                     parent=self._root,
                 )
                 self._destroy()
@@ -204,12 +200,11 @@ def _update(self):
             # Update final state
             if self._multi_video_mode:
                 self._video_progress.set(self._total_videos)
-                self._video_progress_label["text"] = (
-                    f"Completed {self._total_videos} of {self._total_videos} videos"
-                )
-                self._events_label["text"] = f"Total Events Found: {self._total_events}"
+                self._video_progress_label["text"] = f"Scanned {self._total_videos} Videos"
+                self._events_label["text"] = f"Total Events: {self._total_events}"
+                self._current_video_label.config(text=f"{self._current_video_name}")
             else:
-                self._events_label["text"] = f"Events Found: {self._num_events}"
+                self._events_label["text"] = f"Total Events: {self._num_events}"
 
             self._progress.set(self._expected_num_frames)
             self._elapsed_label["text"] = f"Elapsed: {self._elapsed}"
@@ -243,11 +238,9 @@ def _update(self):
             self._video_progress_label["text"] = (
                 f"Video {self._current_video_index + 1} of {self._total_videos}"
             )
-            self._events_label["text"] = (
-                f"Events Found: {self._num_events} (Total: {self._total_events})"
-            )
+            self._events_label["text"] = f"Events: {self._num_events} (Total: {self._total_events})"
         else:
-            self._events_label["text"] = f"Events Found: {self._num_events}"
+            self._events_label["text"] = f"Events: {self._num_events}"
 
         self._elapsed_label["text"] = f"Elapsed: {self._elapsed}"
         self._remaining_label["text"] = f"Time Remaining:\n{self._remaining}"
@@ -271,8 +264,13 @@ def _destroy(self):
         logger.debug("root destroyed")
 
     def prompt_stop(self):
-        if self._scanner.is_stopped() and self._scan_finished.is_set():
-            return
+        with self._scanner_lock:
+            if (
+                self._scanner is not None
+                and self._scanner.is_stopped()
+                and self._scan_finished.is_set()
+            ):
+                return
         if messagebox.askyesno(
             title="Stop scan?",
             message="Are you sure you want to stop the current scan?",
@@ -282,10 +280,12 @@ def prompt_stop(self):
             self._destroy()
 
     def stop(self):
-        self._stopped = True
-        if not self._scanner.is_stopped():
-            logger.debug("stopping scan thread")
-            self._scanner.stop()
+        with self._scanner_lock:
+            self._stopped = True
+            if self._scanner is not None and not self._scanner.is_stopped():
+                logger.debug("stopping scan thread")
+                self._scanner.stop()
+        if self._scan_thread.is_alive():
             self._scan_thread.join()
 
     def show(self):
@@ -328,31 +328,25 @@ def _do_scan(self):
 
         try:
             for i, settings in enumerate(self._settings_list):
-                if self._stopped:
-                    break
-
                 self._current_video_index = i
 
                 # Update video label in multi-video mode
                 if self._multi_video_mode and self._current_video_label:
-                    video_name = Path(settings.get("input")[0]).name
-                    # Schedule UI update on main thread
-                    self._root.after(
-                        0,
-                        lambda n=video_name: self._current_video_label.config(text=f"Current: {n}"),
-                    )
+                    self._current_video_name = Path(settings.get("input")[0]).name
 
-                # Create new scanner for each video (except the first which is already created)
-                if i > 0:
+                # Create scanner for this video
+                with self._scanner_lock:
+                    if self._stopped:
+                        break
                     self._scanner = init_scanner(settings)
                     self._scanner.set_callbacks(
                         scan_started=self._on_scan_started,
                         processed_frame=self._on_processed_frame,
                     )
-                    # Reset per-video state
-                    self._frames_processed = 0
-                    self._num_events = 0
-                    self._progress.set(0)
+                # Reset per-video state
+                self._frames_processed = 0
+                self._num_events = 0
+                self._progress.set(0)
 
                 logger.info(
                     f"Scanning video {i + 1} of {self._total_videos}: {settings.get('input')[0]}"
@@ -364,7 +358,7 @@ def _do_scan(self):
                 self._total_events += len(result.event_list)
                 self._total_frames_processed = total_frames
 
-                logger.info(f"Video {i + 1} complete: {len(result.event_list)} events found")
+                logger.info(f"Finished scanning video: {len(result.event_list)} events found")
 
         except Exception as ex:
             self._scan_exception = ex