worker: fix deadlock when LoggingThread wrote into its own Queue

If self._hub.upload_task_log() called self._queue.put(), it would cause
deadlock because

1. self._queue uses locks that are not reentrant.
2. it will block if the Queue is already full.

Co-authored-by: Kamil Dudka <[email protected]>
Co-authored-by: Lukáš Zaoral <[email protected]>

Author: lzaoral

kobo/worker/logger.py

@@ -24,6 +24,7 @@ def __init__(self, hub, task_id, *args, **kwargs):
         self._buffer_size = kwargs.pop('buffer_size', 256)
         self._queue = queue.Queue(maxsize=self._buffer_size)
         self._event = threading.Event()
+        self._in_logger_call = False
         self._running = True
         self._send_time = 0
         self._send_data = b""
@@ -88,8 +89,24 @@ def run(self):
 
     def write(self, data):
         """Add data to the queue and set the event for sending queue content."""
-        self._queue.put(data)
-        self._event.set()
+        if threading.get_ident() != self.ident:
+            self._queue.put(data)
+            self._event.set()
+
+        # If self._hub.upload_task_log() called self._queue.put(), it would
+        # cause deadlock because self._queue uses locks that are not reentrant
+        # and queue may already be full.
+        #
+        # Log only data with printable characters.
+        elif self._logger and data.strip():
+            # Prevent infinite recursion if this thread is also used for the
+            # logger output.
+            if self._in_logger_call:
+                return
+
+            self._in_logger_call = True
+            self._logger.log_error("Error in LoggingThread: %r", data)
+            self._in_logger_call = False
 
     def stop(self):
         """Send remaining data to hub and finish."""