From 5587a45eb2096891f45c52e2f4efc413849bcbab Mon Sep 17 00:00:00 2001
From: Ben Darnell <ben@bendarnell.com>
Date: Mon, 3 Sep 2012 12:00:26 -0700
Subject: [PATCH] Add gen.YieldFuture.

---
 tornado/gen.py                  | 19 +++++++++++++++++++
 tornado/test/concurrent_test.py | 20 ++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/tornado/gen.py b/tornado/gen.py
index 506697d7b..bc0f935dc 100644
--- a/tornado/gen.py
+++ b/tornado/gen.py
@@ -69,6 +69,7 @@ import operator
 import sys
 import types
 
+from tornado.ioloop import IOLoop
 from tornado.stack_context import ExceptionStackContext
 
 
@@ -247,6 +248,24 @@ class Task(YieldPoint):
         return self.runner.pop_result(self.key)
 
 
+class YieldFuture(YieldPoint):
+    def __init__(self, future, io_loop=None):
+        self.future = future
+        self.io_loop = io_loop or IOLoop.instance()
+
+    def start(self, runner):
+        self.runner = runner
+        self.key = object()
+        runner.register_callback(self.key)
+        self.io_loop.add_future(self.future, runner.result_callback(self.key))
+
+    def is_ready(self):
+        return self.runner.is_ready(self.key)
+
+    def get_result(self):
+        return self.runner.pop_result(self.key).result()
+
+
 class Multi(YieldPoint):
     """Runs multiple asynchronous operations in parallel.
 
diff --git a/tornado/test/concurrent_test.py b/tornado/test/concurrent_test.py
index 87f590e15..2cf371894 100644
--- a/tornado/test/concurrent_test.py
+++ b/tornado/test/concurrent_test.py
@@ -158,6 +158,26 @@ class ClientTestMixin(object):
         self.wait()
         self.assertRaisesRegexp(CapError, "already capitalized", future.result)
 
+    def test_generator(self):
+        @gen.engine
+        def f():
+            result = yield gen.YieldFuture(self.client.capitalize("hello"),
+                                           io_loop=self.io_loop)
+            self.assertEqual(result, "HELLO")
+            self.stop()
+        f()
+        self.wait()
+
+    def test_generator_error(self):
+        @gen.engine
+        def f():
+            with self.assertRaisesRegexp(CapError, "already capitalized"):
+                 yield gen.YieldFuture(self.client.capitalize("HELLO"),
+                                       io_loop=self.io_loop)
+            self.stop()
+        f()
+        self.wait()
+
 
 class ManualClientTest(ClientTestMixin, AsyncTestCase, LogTrapTestCase):
     client_class = ManualCapClient
-- 
2.47.3