From: Ben Darnell <ben@bendarnell.com>
Date: Sun, 20 May 2018 15:28:03 +0000 (-0400)
Subject: asyncio: Fix a race between close and initialize
X-Git-Tag: v5.1.0b1~10^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F2395%2Fhead;p=thirdparty%2Ftornado.git

asyncio: Fix a race between close and initialize

The close method of one IOLoop could race with the initialize method
of another one, leading to KeyErrors raised in close().

Fixes #2367
---

diff --git a/tornado/platform/asyncio.py b/tornado/platform/asyncio.py
index b6a490afa..e0042e1d9 100644
--- a/tornado/platform/asyncio.py
+++ b/tornado/platform/asyncio.py
@@ -62,8 +62,13 @@ class BaseAsyncIOLoop(IOLoop):
             self.remove_handler(fd)
             if all_fds:
                 self.close_fd(fileobj)
-        self.asyncio_loop.close()
+        # Remove the mapping before closing the asyncio loop. If this
+        # happened in the other order, we could race against another
+        # initialize() call which would see the closed asyncio loop,
+        # assume it was closed from the asyncio side, and do this
+        # cleanup for us, leading to a KeyError.
         del IOLoop._ioloop_for_asyncio[self.asyncio_loop]
+        self.asyncio_loop.close()
 
     def add_handler(self, fd, handler, events):
         fd, fileobj = self.split_fd(fd)
diff --git a/tornado/test/ioloop_test.py b/tornado/test/ioloop_test.py
index 646a1d431..b38d0ba32 100644
--- a/tornado/test/ioloop_test.py
+++ b/tornado/test/ioloop_test.py
@@ -458,6 +458,16 @@ class TestIOLoop(AsyncTestCase):
             client.close()
             server.close()
 
+    @gen_test
+    def test_init_close_race(self):
+        # Regression test for #2367
+        def f():
+            for i in range(10):
+                loop = IOLoop()
+                loop.close()
+
+        yield gen.multi([self.io_loop.run_in_executor(None, f) for i in range(2)])
+
 
 # Deliberately not a subclass of AsyncTestCase so the IOLoop isn't
 # automatically set as current.