GH-85760: Fix race in calling process_exited callback too early (GH-97009)

(cherry picked from commit 282edd7)

Co-authored-by: Kumar Aditya <[email protected]>

Author: miss-islington

Lib/asyncio/unix_events.py

@@ -223,7 +223,8 @@ async def _make_subprocess_transport(self, protocol, args, shell,
         return transp
 
     def _child_watcher_callback(self, pid, returncode, transp):
-        self.call_soon_threadsafe(transp._process_exited, returncode)
+        # Skip one iteration for callbacks to be executed
+        self.call_soon_threadsafe(self.call_soon, transp._process_exited, returncode)
 
     async def create_unix_connection(
             self, protocol_factory, path=None, *,

Misc/NEWS.d/next/Library/2022-09-22-11-50-29.gh-issue-85760.DETTPd.rst

@@ -0,0 +1 @@
+Fix race condition in :mod:`asyncio` where :meth:`~asyncio.SubprocessProtocol.process_exited` called before the :meth:`~asyncio.SubprocessProtocol.pipe_data_received` leading to inconsistent output. Patch by Kumar Aditya.