From: Ben Darnell <ben@bendarnell.com>
Date: Mon, 15 Sep 2014 02:38:14 +0000 (-0400)
Subject: Capture stack context in gen.engine's wrapper function.
X-Git-Tag: v4.1.0b1~90^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f40d39b;p=thirdparty%2Ftornado.git

Capture stack context in gen.engine's wrapper function.

This was an error that went unnoticed in earlier versions
because Futures passed through exceptions in their callbacks.
---

diff --git a/tornado/gen.py b/tornado/gen.py
index 4bb82d422..d0d0b5ef2 100644
--- a/tornado/gen.py
+++ b/tornado/gen.py
@@ -109,7 +109,10 @@ def engine(func):
                 raise ReturnValueIgnoredError(
                     "@gen.engine functions cannot return values: %r" %
                     (future.result(),))
-        future.add_done_callback(final_callback)
+        # The engine interface doesn't give us any way to return
+        # errors but to raise them into the stack context.
+        # Save the stack context here to use when the Future has resolved.
+        future.add_done_callback(stack_context.wrap(final_callback))
     return wrapper