instant cancel during preprocessing (dont wait for thread to finish)

app.py

@@ -811,6 +811,11 @@ def gradio_main():
             t.start()
             while t.is_alive():
                 t.join(timeout=3)
+                if _training_cancel.is_set():
+                    _training_cancel.clear()
+                    _log("[CANCELLED] Stopped during preprocessing")
+                    yield _log_text(), gr.Button(visible=True), gr.Button(visible=False), gr.File()
+                    return
                 if len(_train_log_lines) > _preprocess_log_len:
                     _preprocess_log_len = len(_train_log_lines)
                     yield _log_text(), gr.Button(visible=False), gr.Button(visible=True), gr.File()
@@ -819,12 +824,6 @@ def gradio_main():
                 raise _preprocess_error[0]
             result = _preprocess_result[0]
 
-            if _training_cancel.is_set():
-                _training_cancel.clear()
-                _log("[CANCELLED] Stopped during preprocessing")
-                yield _log_text(), gr.Button(visible=True), gr.Button(visible=False), gr.File()
-                return
-
             processed = result.get("processed", 0)
             failed = result.get("failed", 0)
             total = result.get("total", 0)