Add middleware that apps can use to handle graceful timeout signal

uwsgi 2.0.22+ offers option to send a user-defined signal at for a
"graceful" timeout before the real harakiri occurs.

gunicorn sends SIGABRT (signal 6) as graceful timeout signal before
sending SIGKILL.

Apps can use this middleware to log a traceback indicating what code was
executing when the graceful timeout signal was received.

ansible_base/lib/middleware/logging/__init__.py

@@ -1,3 +1,3 @@
-from ansible_base.lib.middleware.logging.log_request import LogRequestMiddleware
+from ansible_base.lib.middleware.logging.log_request import LogRequestMiddleware, LogTracebackMiddleware
 
-__all__ = ('LogRequestMiddleware',)
+__all__ = ('LogRequestMiddleware', 'LogTracebackMiddleware')

ansible_base/lib/middleware/logging/log_request.py

@@ -1,10 +1,33 @@
 import logging
+import traceback
+import uuid
 
 from ansible_base.lib.logging import thread_local
 
 logger = logging.getLogger(__name__)
 
 
+class LogTracebackMiddleware:
+    transactions = {}
+
+    @classmethod
+    def handle_signal(cls, *args):
+        for t_id, request in LogTracebackMiddleware.transactions.items():
+            logger.error(f"Catching graceful timeout signal for {request.method} path: {request.path}")
+            logger.error(f"Received graceful timeout signal while in stack: {''.join(traceback.format_stack())}")
+
+    def __init__(self, get_response):
+        self.get_response = get_response
+
+    def __call__(self, request):
+        t_id = str(uuid.uuid4())
+        LogTracebackMiddleware.transactions[t_id] = request
+        try:
+            return self.get_response(request)
+        finally:
+            LogTracebackMiddleware.transactions.pop(t_id)
+
+
 class LogRequestMiddleware:
     """
     Inject the request into the thread local so that it can be accessed by the logging filter.

test_app/apps.py

@@ -1,6 +1,14 @@
+import signal
+
 from django.apps import AppConfig
 
+from ansible_base.lib.middleware.logging import LogTracebackMiddleware
+
 
 class TestAppConfig(AppConfig):
     default_auto_field = 'django.db.models.BigAutoField'
     name = 'test_app'
+
+    def ready(self):
+        super().ready()
+        signal.signal(signal.SIGSYS, LogTracebackMiddleware.handle_signal)

test_app/settings.py

@@ -86,6 +86,7 @@
     'django.middleware.clickjacking.XFrameOptionsMiddleware',
     'crum.CurrentRequestUserMiddleware',
     'ansible_base.lib.middleware.logging.LogRequestMiddleware',
+    'ansible_base.lib.middleware.logging.LogTracebackMiddleware',
 ]
 
 REST_FRAMEWORK = {