Immediately flush debug messages (#582)

Author: brownbaerchen

pySDC/core/controller.py

@@ -92,7 +92,25 @@ def __setup_custom_logger(level=None, log_to_file=None, fname=None):
             file_handler = None
 
         std_formatter = logging.Formatter(fmt='%(name)s - %(levelname)s: %(message)s')
-        std_handler = logging.StreamHandler(sys.stdout)
+
+        if level <= logging.DEBUG:
+            import warnings
+
+            warnings.warn('Running with debug output will degrade performance as all output is immediately flushed.')
+
+            class StreamFlushingHandler(logging.StreamHandler):
+                """
+                This will immediately flush any messages to the output.
+                """
+
+                def emit(self, record):
+                    super().emit(record)
+                    self.flush()
+
+            std_handler = StreamFlushingHandler(sys.stdout)
+        else:
+            std_handler = logging.StreamHandler(sys.stdout)
+
         std_handler.setFormatter(std_formatter)
 
         # instantiate logger