bpo-23846: Fix ProactorEventLoop._write_to_self() (GH-11566)

asyncio.ProactorEventLoop now catchs and logs send errors when the
self-pipe is full: BaseProactorEventLoop._write_to_self() now catchs
and logs OSError exceptions, as done by
BaseSelectorEventLoop._write_to_self().

Lib/asyncio/proactor_events.py

@@ -636,7 +636,13 @@ def _loop_self_reading(self, f=None):
             f.add_done_callback(self._loop_self_reading)
 
     def _write_to_self(self):
-        self._csock.send(b'\0')
+        try:
+            self._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,

Misc/NEWS.d/next/Library/2019-01-15-13-31-30.bpo-23846.LT_qL8.rst

@@ -0,0 +1,2 @@
+:class:`asyncio.ProactorEventLoop` now catchs and logs send errors when the
+self-pipe is full.