Merge pull request #1299 from gevent/issue1295

Be more careful handling NOT_ERROR during interpreter shutdown.

CHANGES.rst

@@ -28,6 +28,9 @@
   ``AsyncEvent``. Note that the order in which semaphore links are
   called is not specified. See :issue:`1287`, reported by Dan Milon.
 
+- Improve safety of handling exceptions during interpreter shutdown.
+  See :issue:`1295` reported by BobDenar1212.
+
 
 1.3.7 (2018-10-12)
 ==================

src/gevent/_ffi/loop.py

@@ -137,6 +137,10 @@ class AbstractCallbacks(object):
             # Depending on when the exception happened, the watcher
             # may or may not have been stopped. We need to make sure its
             # memory stays valid so we can stop it at the ev level if needed.
+            # If its loop is gone, it has already been stopped,
+            # see https://github.com/gevent/gevent/issues/1295 for a case where
+            # that happened
+            if the_watcher.loop is not None:
                 the_watcher.loop._keepaliveset.add(the_watcher)
             return -1
         else:

src/gevent/hub.py

@@ -511,7 +511,9 @@ class Hub(WaitOperationsGreenlet):
         # Unwrap any FileObjectThread we have thrown around sys.stderr
         # (because it can't be used in the hub). Tricky because we are
         # called in error situations when it's not safe to import.
-        stderr = sys.stderr
+        # Be careful not to access sys if we're in the process of interpreter
+        # shutdown.
+        stderr = sys.stderr if sys else None # pylint:disable=using-constant-test
         if type(stderr).__name__ == 'FileObjectThread':
             stderr = stderr.io # pylint:disable=no-member
         return stderr
@@ -521,6 +523,12 @@ class Hub(WaitOperationsGreenlet):
         # traceback.print_exception() as previous versions did.
         # pylint:disable=no-member
         errstream = self.exception_stream
+        if not errstream: # pragma: no cover
+            # If the error stream is gone, such as when the sys dict
+            # gets cleared during interpreter shutdown,
+            # don't cause follow-on errors.
+            # See https://github.com/gevent/gevent/issues/1295
+            return
 
         if value is None:
             errstream.write('%s\n' % type.__name__)