python · vstinner · Sep 12, 2020 · Sep 11, 2020
diff --git a/Lib/asyncio/proactor_events.py b/Lib/asyncio/proactor_events.py
@@ -793,8 +793,17 @@ def _loop_self_reading(self, f=None):
            f.add_done_callback(self._loop_self_reading)

    def _write_to_self(self):
+        # This may be called from a different thread, possibly after
+        # _close_self_pipe() has been called or even while it is
+        # running.  Guard for self._csock being None or closed.  When
+        # a socket is closed, send() raises OSError (with errno set to
+        # EBADF, but let's not rely on the exact error code).
+        csock = self._csock
+        if csock is None:
+            return
+
        try:
-            self._csock.send(b'\0')
+            csock.send(b'\0')
        except OSError:
            if self._debug:
                logger.debug("Fail to write a null byte into the "

diff --git a/Lib/asyncio/selector_events.py b/Lib/asyncio/selector_events.py
@@ -133,14 +133,16 @@ def _write_to_self(self):
        # a socket is closed, send() raises OSError (with errno set to
        # EBADF, but let's not rely on the exact error code).
        csock = self._csock
-        if csock is not None:
-            try:
-                csock.send(b'\0')
-            except OSError:
-                if self._debug:
-                    logger.debug("Fail to write a null byte into the "
-                                 "self-pipe socket",
-                                 exc_info=True)
+        if csock is None:
+            return
+
+        try:
+            csock.send(b'\0')
+        except OSError:
+            if self._debug:
+                logger.debug("Fail to write a null byte into the "
+                             "self-pipe socket",
+                             exc_info=True)

    def _start_serving(self, protocol_factory, sock,
                       sslcontext=None, server=None, backlog=100,

diff --git a/Misc/NEWS.d/next/Library/2020-09-11-12-38-55.bpo-39651.JMp9l2.rst b/Misc/NEWS.d/next/Library/2020-09-11-12-38-55.bpo-39651.JMp9l2.rst
@@ -0,0 +1,3 @@
+Fix a race condition in the ``call_soon_threadsafe()`` method of
+``asyncio.ProactorEventLoop``: do nothing if the self-pipe socket has been
+closed.