Add a lock around TcpClient.close() to try avoiding None.close()

telethon/extensions/tcp_client.py

@@ -3,12 +3,15 @@ import errno
 import socket
 from datetime import timedelta
 from io import BytesIO, BufferedWriter
+from threading import Lock
 
 
 class TcpClient:
     def __init__(self, proxy=None, timeout=timedelta(seconds=5)):
         self._proxy = proxy
         self._socket = None
+        self._closing_lock = Lock()
+
         if isinstance(timeout, timedelta):
             self._timeout = timeout.seconds
         elif isinstance(timeout, int) or isinstance(timeout, float):
@@ -48,8 +51,13 @@ class TcpClient:
 
     def close(self):
         """Closes the connection"""
+        if self._closing_lock.locked():
+            # Already closing, no need to close again (avoid None.close())
+            return
+
+        with self._closing_lock:
             try:
-            if self.connected:
+                if self._socket is not None:
                     self._socket.shutdown(socket.SHUT_RDWR)
                     self._socket.close()
             except OSError: