From 2b44fac4ecf273aadc97dbcaa5abf1e3a1ee7dff Mon Sep 17 00:00:00 2001
From: Ben Darnell <ben@bendarnell.com>
Date: Thu, 4 Nov 2010 11:47:34 -0700
Subject: [PATCH] Check for a closed connection in _add_io_state.

Closes #163.
---
 tornado/iostream.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tornado/iostream.py b/tornado/iostream.py
index 2897fdc7..4f321d55 100644
--- a/tornado/iostream.py
+++ b/tornado/iostream.py
@@ -359,6 +359,9 @@ class IOStream(object):
             raise IOError("Stream is closed")
 
     def _add_io_state(self, state):
+        if socket is None:
+            # connection has been closed, so there can be no future events
+            return
         if not self._state & state:
             self._state = self._state | state
             self.io_loop.update_handler(self.socket.fileno(), self._state)