concurrent: Fix importability of tornado.wsgi on app engine

2018-01-21 20:12:06 -05:00 · 2018-01-21 20:12:06 -05:00 · 6e8a137e68
parent 606f0b5e90
commit 6e8a137e68
1 changed files with 6 additions and 5 deletions
--- a/tornado/concurrent.py
+++ b/tornado/concurrent.py
@ -337,11 +337,12 @@ class Future(object):

    def _set_done(self):
        self._done = True
-        from tornado.ioloop import IOLoop
-        loop = IOLoop.current()
-        for cb in self._callbacks:
-            loop.add_callback(cb, self)
-        self._callbacks = None
+        if self._callbacks:
+            from tornado.ioloop import IOLoop
+            loop = IOLoop.current()
+            for cb in self._callbacks:
+                loop.add_callback(cb, self)
+            self._callbacks = None

    # On Python 3.3 or older, objects with a destructor part of a reference
    # cycle are never destroyed. It's no longer the case on Python 3.4 thanks to