Potential server crash if running Python 3.10 w/ Sanic 20.12 (#2400)

sanic/__version__.py

@@ -1 +1 @@
-__version__ = "20.12.5"
+__version__ = "20.12.6"

sanic/app.py

@@ -2,6 +2,7 @@
 import logging.config
 import os
 import re
+import sys
 
 from asyncio import CancelledError, Protocol, ensure_future, get_event_loop
 from collections import defaultdict, deque
@@ -65,6 +66,18 @@ def __init__(
         if configure_logging:
             logging.config.dictConfig(log_config or LOGGING_CONFIG_DEFAULTS)
 
+        if sys.version_info >= (3, 10):
+            error_logger.error(
+                "Unsupported version of Python has been detected.\n\nPython "
+                f"version {sys.version} is not supported by this version of "
+                "Sanic. There is a security advisory that has been issued for "
+                "Sanic v20.12 while running Python 3.10+. You should either "
+                "use a supported version of Python (v3.6 - v3.9) or upgrade "
+                "Sanic to v21+.\n\nPlease see https://github.com/sanic-org/"
+                "sanic/security/advisories/GHSA-7p79-6x2v-5h88 for "
+                "more information.\n"
+            )
+
         self.name = name
         self.asgi = False
         self.router = router or Router(self)

sanic/server.py

@@ -169,7 +169,11 @@ def __init__(
         self.request_class = self.app.request_class or Request
         self.is_request_stream = self.app.is_request_stream
         self._is_stream_handler = False
-        self._not_paused = asyncio.Event(loop=deprecated_loop)
+        self._not_paused = (
+            asyncio.Event()
+            if sys.version_info >= (3, 10)
+            else asyncio.Event(loop=deprecated_loop)
+        )
         self._total_request_size = 0
         self._request_timeout_handler = None
         self._response_timeout_handler = None