bpo-26133: Dont unsubscribe signals in UNIX even loop on interpreter shutdown (GH-4956) (#4962)

(cherry picked from commit 4a02543)

Author: miss-islington

Lib/asyncio/unix_events.py

@@ -61,8 +61,14 @@ def _socketpair(self):
 
     def close(self):
         super().close()
-        for sig in list(self._signal_handlers):
-            self.remove_signal_handler(sig)
+        if not sys.is_finalizing():
+            for sig in list(self._signal_handlers):
+                self.remove_signal_handler(sig)
+        else:
+            warinigs.warn(f"Closing the loop {self!r} on interpreter shutdown "
+                          f"stage, signal unsubsription is disabled",
+                          ResourceWarning,
+                          source=self)
 
     def _process_self_data(self, data):
         for signum in data:

Misc/NEWS.d/next/Library/2017-12-21-11-08-42.bpo-26133.mt81QV.rst

@@ -0,0 +1 @@
+Don't unsubscribe signals in asyncio UNIX event loop on interpreter shutdown.