iostream: check that stream is open before trying to read (#2670)

diff --git a/tornado/iostream.py b/tornado/iostream.py
index 6ea748a541d16068634d581c444b8468e667d45e..ee305922dc084b47e4368b0ef631eb6c2aec407b 100644 (file)
--- a/tornado/iostream.py
+++ b/tornado/iostream.py
@@ -794,6 +794,7 @@ class BaseIOStream(object):
             self._read_from_buffer(pos)
 
     def _start_read(self) -> Future:
+        self._check_closed()  # Before reading, check that stream is not closed.
         assert self._read_future is None, "Already reading"
         self._read_future = Future()
         return self._read_future