work around for null byte issue after truncating

filterwidget.py

@@ -43,6 +43,14 @@ class FilterTask(QRunnable):
             # print("starting thread ", threading.currentThread())
             self.on_before()
 
+            # delay the filtering. This work arounds a race condition. For some reasons, even though we have locks
+            # to ensure that only one thread writes to the target file, it happened that the file was not correctly
+            # truncated and started with null bytes. Sometimes several MB of null bytes. My guess is that this is
+            # caused by async write operations.
+            time.sleep(0.5)
+            if self.aborted:
+                self.on_finish()
+
             for listener in self.filter_match_found_listeners:
                 listener(-1, -1)  # notify listeners that a new search started
 
@@ -138,6 +146,9 @@ class FilterWidget(QWidget):
         if self.filter_task:
             # print("cancel started ", time.time())
             self.filter_task.aborted = True
+            # wait until the previous search is aborted
+            with self._lock:
+                pass
 
     def reset_filter(self):
         self.filter_model.truncate()