Issue #20455: asyncio: write a new write pipe transport class for proactor (on

Windows) instead of using the "duplex" pipe transport. The new class uses a
simpler overlapped read to be notified when the pipe is closed. So the protocol
doesn't need to implement eof_received(): connection_lost() is called instead.
_UnixWritePipeTransport has the same approach.

Lib/asyncio/proactor_events.py

@@ -205,7 +205,7 @@ class _ProactorReadPipeTransport(_ProactorBasePipeTransport,
                     self.close()
 
 
-class _ProactorWritePipeTransport(_ProactorBasePipeTransport,
+class _ProactorBaseWritePipeTransport(_ProactorBasePipeTransport,
                                   transports.WriteTransport):
     """Transport for write pipes."""
 
@@ -286,8 +286,27 @@ class _ProactorWritePipeTransport(_ProactorBasePipeTransport,
         self._force_close(None)
 
 
+class _ProactorWritePipeTransport(_ProactorBaseWritePipeTransport):
+    def __init__(self, *args, **kw):
+        super().__init__(*args, **kw)
+        self._read_fut = self._loop._proactor.recv(self._sock, 16)
+        self._read_fut.add_done_callback(self._pipe_closed)
+
+    def _pipe_closed(self, fut):
+        if fut.cancelled():
+            # the transport has been closed
+            return
+        assert fut is self._read_fut, (fut, self._read_fut)
+        self._read_fut = None
+        assert fut.result() == b''
+        if self._write_fut is not None:
+            self._force_close(exc)
+        else:
+            self.close()
+
+
 class _ProactorDuplexPipeTransport(_ProactorReadPipeTransport,
-                                   _ProactorWritePipeTransport,
+                                   _ProactorBaseWritePipeTransport,
                                    transports.Transport):
     """Transport for duplex pipes."""
 
@@ -299,7 +318,7 @@ class _ProactorDuplexPipeTransport(_ProactorReadPipeTransport,
 
 
 class _ProactorSocketTransport(_ProactorReadPipeTransport,
-                               _ProactorWritePipeTransport,
+                               _ProactorBaseWritePipeTransport,
                                transports.Transport):
     """Transport for connected sockets."""
 
@@ -353,15 +372,10 @@ class BaseProactorEventLoop(base_events.BaseEventLoop):
         return _ProactorReadPipeTransport(self, sock, protocol, waiter, extra)
 
     def _make_write_pipe_transport(self, sock, protocol, waiter=None,
-                                   extra=None, check_for_hangup=True):
-        if check_for_hangup:
-            # We want connection_lost() to be called when other end closes
-            return _ProactorDuplexPipeTransport(self,
-                                                sock, protocol, waiter, extra)
-        else:
-            # If other end closes we may not notice for a long time
-            return _ProactorWritePipeTransport(self, sock, protocol, waiter,
-                                               extra)
+                                   extra=None):
+        # We want connection_lost() to be called when other end closes
+        return _ProactorWritePipeTransport(self,
+                                           sock, protocol, waiter, extra)
 
     def close(self):
         if self._proactor is not None: