Merge pull request #2815 from bdarnell/thread-selector

asyncio: Improve support Python 3.8 on Windows

diff --cc tornado/platform/asyncio.py
index 5a4f53e2744899bf1a27b58d7f0a0ebbf78c5f70,390d5259be33ba9a44175f0f95820cdd3d57977c..fc88f918e6301626442e096940004dfca5fe04cf
--- 1/tornado/platform/asyncio.py
--- 2/tornado/platform/asyncio.py
+++ b/tornado/platform/asyncio.py
@@@ -67,10 -111,10 +111,10 @@@ class BaseAsyncIOLoop(IOLoop)
  
          self._thread_identity = 0
  
 -        super(BaseAsyncIOLoop, self).initialize(**kwargs)
 +        super().initialize(**kwargs)
  
          def assign_thread_identity() -> None:
-             self._thread_identity = get_ident()
+             self._thread_identity = threading.get_ident()
  
          self.add_callback(assign_thread_identity)
  

diff --cc tornado/test/httpclient_test.py
Simple merge

diff --cc tornado/test/ioloop_test.py
Simple merge

diff --cc tornado/test/iostream_test.py
index bf713aa86aa3e7a56bb5f3509ec4d9ac1ff9f544,67d6438cd76127592cf86a022f87db2fc1e224b7..a43aa64cad3cf6af21b64fb4a576d998cbd5c675
--- 1/tornado/test/iostream_test.py
--- 2/tornado/test/iostream_test.py
+++ b/tornado/test/iostream_test.py
@@@ -943,8 -960,9 +960,9 @@@ class TestIOStreamStartTLS(AsyncTestCas
              self.server_stream.close()
          if self.client_stream is not None:
              self.client_stream.close()
+         self.io_loop.remove_handler(self.listener.fileno())
          self.listener.close()
 -        super(TestIOStreamStartTLS, self).tearDown()
 +        super().tearDown()
  
      def accept(self, connection, address):
          if self.server_stream is not None:

diff --cc tornado/test/runtests.py
Simple merge

diff --cc tornado/test/simple_httpclient_test.py
Simple merge