Ignore BusyCursor when called from thread

pyqtgraph/widgets/BusyCursor.py

@@ -9,13 +9,19 @@ class BusyCursor(object):
         with pyqtgraph.BusyCursor():
             doLongOperation()
 
-    May be nested.
+    May be nested. If called from a non-gui thread, then the cursor will not be affected.
     """
     active = []
 
     def __enter__(self):
+        app = QtCore.QCoreApplication.instance()
+        isGuiThread = (app is not None) and (QtCore.QThread.currentThread() == app.thread())
+        if isGuiThread and QtGui.QApplication.instance() is not None:
             QtGui.QApplication.setOverrideCursor(QtGui.QCursor(QtCore.Qt.WaitCursor))
             BusyCursor.active.append(self)
+            self._active = True
+        else:
+            self._active = False
 
     def __exit__(self, *args):
         if self._active: