refactor: implement thread-safe hardware operations, port caching, and refined state management in the device controller

src/pygui/backend/controllers/session_controller.py

@@ -232,7 +232,8 @@ class SessionController(QObject):
     def setMode(self, mode: str) -> None:
         if mode == self._mode:
             return
-        self.stopStream()
+        if mode != "live":
+            self.stopStream()
         self._play_timer.stop()
         self._mode = mode
         self.modeChanged.emit()
@@ -394,6 +395,9 @@ class SessionController(QObject):
     @Slot(str, str)
     @slot_error_boundary
     def startStream(self, port: str, family_code: str = "") -> None:
+        if self._reader is not None:
+            log.warning("startStream: StreamReader is already running.")
+            return
 
         from pygui.backend.wafer.wafer_layouts import load_layout_for_wafer_id
         from pygui.serialcomm.serial_port import SerialPort  # transport open
@@ -449,13 +453,24 @@ class SessionController(QObject):
         cmd = b"D2" + SerialPort.COMMAND_PAD.encode()
         transport.write(cmd)
 
+        import weakref
+        weak_self = weakref.ref(self)
+
         def on_error(exc: Exception):
             log.error("Live stream error: %s", exc)
-            self._liveError.emit()
+            ref = weak_self()
+            if ref is not None:
+                ref._liveError.emit()
+                ref.stopStream()
+
+        def on_frame(frame: Frame):
+            ref = weak_self()
+            if ref is not None:
+                ref._liveFrame.emit(frame)
 
         self._reader = StreamReader(
             transport, parse_binary_frame,
-            on_frame=lambda f: self._liveFrame.emit(f),
+            on_frame=on_frame,
             on_error=on_error,
             family_code=family_code or "A")
         self._reader.start()
@@ -474,10 +489,9 @@ class SessionController(QObject):
         self.liveStatsChanged.emit()
         if self._reader:
             transport = self._reader._transport
-            self._reader.stop()
-            self._reader = None
 
             # Send 'D2S' command padded to 512 bytes to stop the stream
+            # Send BEFORE stopping the reader which will close the port on thread exit
             if transport and transport.is_open:
                 try:
                     cmd = b"D2S" + (b"F" * 509)
@@ -486,6 +500,9 @@ class SessionController(QObject):
                 except Exception as exc:
                     log.error("Error sending stop command: %s", exc)
 
+            self._reader.stop()
+            self._reader = None
+
         self.stateChanged.emit()
         self.stopRecording()