Merge branch 'master' into avoid-threading-identity

diff --cc tornado/platform/asyncio.py
index a5545a047e83083a8fda5578b23aedc48ffbbcc7,909cd7877691643defaa8ea6c3c3b4e300a90662..ca671ac64d4699529c1614ddccc5022fea31d115
--- 1/tornado/platform/asyncio.py
--- 2/tornado/platform/asyncio.py
+++ b/tornado/platform/asyncio.py
@@@ -137,10 -137,15 +137,8 @@@ class BaseAsyncIOLoop(IOLoop)
                  f"IOLoop {existing_loop} already associated with asyncio loop {asyncio_loop}"
              )
  
-         IOLoop._ioloop_for_asyncio[asyncio_loop] = self
 -        self._thread_identity = 0
--
          super().initialize(**kwargs)
  
 -        def assign_thread_identity() -> None:
 -            self._thread_identity = threading.get_ident()
 -
 -        self.add_callback(assign_thread_identity)
 -
      def close(self, all_fds: bool = False) -> None:
          self.closing = True
          for fd in list(self.handlers):