Make sure we retrieve the data atomically

Ignore any requests to sync the device while the previous sync is still
ongoing. This should be the exception anyway, we shouldn't get another
"connected" signal from the device while we're syncing.

tuhi/wacom.py

@@ -136,6 +136,8 @@ class WacomDevice(GObject.Object):
         self.height = WACOM_SLATE_HEIGHT
         self.name = device.name
 
+        self._is_running = False
+
         device.connect_gatt_value(WACOM_CHRC_LIVE_PEN_DATA_UUID,
                                   self._on_pen_data_changed)
         device.connect_gatt_value(WACOM_OFFLINE_CHRC_PEN_DATA_UUID,
@@ -571,10 +573,16 @@ class WacomDevice(GObject.Object):
             logger.warning("no data, please make sure the LED is blue and the button is pressed to switch it back to green")
 
     def run(self):
+        if self._is_running:
+            logger.error('{}: already synching, ignoring this request'.format(self.device.address))
+            return
+
         logger.debug('{}: starting'.format(self.device.address))
+        self._is_running = True
         try:
             self.retrieve_data()
         finally:
+            self._is_running = False
             self.emit("done")
 
     def start(self):