From 1c3d22fcf5305ebe506c4ac1e5ab760b7ddf4c04 Mon Sep 17 00:00:00 2001
From: "A. Jesse Jiryu Davis" <jesse@mongodb.com>
Date: Wed, 18 Feb 2015 08:56:52 -0500
Subject: [PATCH] Fix multiple calls to Event.clear.

---
 tornado/locks.py           | 3 ++-
 tornado/test/locks_test.py | 9 +++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/tornado/locks.py b/tornado/locks.py
index 62d962b815..73cc9e2b8b 100644
--- a/tornado/locks.py
+++ b/tornado/locks.py
@@ -110,7 +110,8 @@ def clear(self):
         
         Calls to `.wait` will block until `.set` is called.
         """
-        self._future = Future()
+        if self._future.done():
+            self._future = Future()
 
     def wait(self, timeout=None):
         """Block until the internal flag is true.
diff --git a/tornado/test/locks_test.py b/tornado/test/locks_test.py
index 49e6199cce..73f0f5911f 100644
--- a/tornado/test/locks_test.py
+++ b/tornado/test/locks_test.py
@@ -206,6 +206,15 @@ def test_event_set_multiple(self):
         e.set()
         self.assertTrue(e.is_set())
 
+    def test_event_wait_clear(self):
+        e = locks.Event()
+        f0 = e.wait()
+        e.clear()
+        f1 = e.wait()
+        e.set()
+        self.assertTrue(f0.done())
+        self.assertTrue(f1.done())
+
 
 if __name__ == '__main__':
     unittest.main()