add on_exit hook

docs/source/settings.rst

@@ -782,6 +782,17 @@ two integers of number of workers after and before change.
 If the number of workers is set for the first time, old_value would be
 None.
 
+on_exit
+~~~~~~~
+*  ::
+
+        def on_exit():
+            pass
+
+Called just before exiting gunicorn.
+
+The callable needs to accept a single instance variable for the Arbiter.
+
 Server Mechanics
 ----------------
 

gunicorn/arbiter.py

@@ -296,6 +296,7 @@ class Arbiter(object):
             self.log.info("Reason: %s", reason)
         if self.pidfile is not None:
             self.pidfile.unlink()
+        self.cfg.on_exit(self)
         sys.exit(exit_status)
 
     def sleep(self):

gunicorn/config.py

@@ -1422,6 +1422,21 @@ class NumWorkersChanged(Setting):
         None.
         """
 
+class OnExit(Setting):
+    name = "on_exit"
+    section = "Server Hooks"
+    validator = validate_callable(1)
+
+    def on_exit(server):
+        pass
+
+    default = staticmethod(on_exit)
+    desc = """\
+        Called just before exiting gunicorn.
+
+        The callable needs to accept a single instance variable for the Arbiter.
+        """
+
 
 class ProxyProtocol(Setting):
     name = "proxy_protocol"