asyncio: a new self-pipe should be created in the child process after fork

Lib/asyncio/proactor_events.py

 """Event loop using a proactor and related classes.
 
 A proactor is a "notify-on-completion" multiplexer.  Currently a
 proactor is only implemented on Windows with IOCP.
 """
 
 __all__ = ['BaseProactorEventLoop']
 
 import socket
 import sys
@@ skipping 471 matching lines @@
             self.call_exception_handler({
                 'message': 'Error on reading from the event loop self pipe',
                 'exception': exc,
                 'loop': self,
             })
         else:
             self._self_reading_future = f
             f.add_done_callback(self._loop_self_reading)
 
     def _write_to_self(self):
+        # The self-pipe must not be shared between two processes: at fork,
+        # create a new pipe to unshare it
+        self._detect_fork()
+
         self._csock.send(b'\0')
 
     def _start_serving(self, protocol_factory, sock,
                        sslcontext=None, server=None):
 
         def loop(f=None):
             try:
                 if f is not None:
                     conn, addr = f.result()
                     if self._debug:
@@ skipping 36 matching lines @@
 
     def _stop_accept_futures(self):
         for future in self._accept_futures.values():
             future.cancel()
         self._accept_futures.clear()
 
     def _stop_serving(self, sock):
         self._stop_accept_futures()
         self._proactor._stop_serving(sock)
         sock.close()