[3.15] gh-119710: fix asyncio Process.wait() to finish on process exit and not wait for closing of pipes (GH-151983) (#154170)

* gh-119710: fix asyncio Process.wait() to finish on process exit and not wait for closing of pipes (GH-151983)
(cherry picked from commit f252132)

Co-authored-by: Tobias Alex-Petersen <tobias.alex.petersen@gmail.com>
Co-authored-by: Kumar Aditya <kumaraditya@python.org>

Author: 3 people

Lib/asyncio/base_subprocess.py

@@ -26,7 +26,6 @@ def __init__(self, loop, protocol, args, shell,
         self._pending_calls = collections.deque()
         self._pipes = {}
         self._finished = False
-        self._pipes_connected = False
 
         if stdin == subprocess.PIPE:
             self._pipes[0] = None
@@ -214,7 +213,6 @@ async def _connect_pipes(self, waiter):
         else:
             if waiter is not None and not waiter.cancelled():
                 waiter.set_result(None)
-            self._pipes_connected = True
 
     def _call(self, cb, *data):
         if self._pending_calls is not None:
@@ -235,6 +233,7 @@ def _process_exited(self, returncode):
         if self._loop.get_debug():
             logger.info('%r exited with return code %r', self, returncode)
         self._returncode = returncode
+
         if self._proc.returncode is None:
             # asyncio uses a child watcher: copy the status into the Popen
             # object. On Python 3.6, it is required to avoid a ResourceWarning.
@@ -243,6 +242,13 @@ def _process_exited(self, returncode):
 
         self._try_finish()
 
+        # gh-119710: Wake up futures waiting for wait() as soon as the process
+        # exits.
+        for waiter in self._exit_waiters:
+            if not waiter.done():
+                waiter.set_result(returncode)
+        self._exit_waiters = None
+
     async def _wait(self):
         """Wait until the process exit and return the process return code.
 
@@ -258,15 +264,7 @@ def _try_finish(self):
         assert not self._finished
         if self._returncode is None:
             return
-        if not self._pipes_connected:
-            # self._pipes_connected can be False if not all pipes were connected
-            # because either the process failed to start or the self._connect_pipes task
-            # got cancelled. In this broken state we consider all pipes disconnected and
-            # to avoid hanging forever in self._wait as otherwise _exit_waiters
-            # would never be woken up, we wake them up here.
-            for waiter in self._exit_waiters:
-                if not waiter.done():
-                    waiter.set_result(self._returncode)
+
         if all(p is not None and p.disconnected
                for p in self._pipes.values()):
             self._finished = True
@@ -276,11 +274,6 @@ def _call_connection_lost(self, exc):
         try:
             self._protocol.connection_lost(exc)
         finally:
-            # wake up futures waiting for wait()
-            for waiter in self._exit_waiters:
-                if not waiter.done():
-                    waiter.set_result(self._returncode)
-            self._exit_waiters = None
             self._loop = None
             self._proc = None
             self._protocol = None

Lib/test/test_asyncio/test_subprocess.py

@@ -111,37 +111,6 @@ def test_subprocess_repr(self):
         )
         transport.close()
 
-    def test_proc_exited_no_invalid_state_error_on_exit_waiters(self):
-        # gh-145541: when _connect_pipes hasn't completed (so
-        # _pipes_connected is False) and the process exits, _try_finish()
-        # sets the result on exit waiters. Then _call_connection_lost() must
-        # not call set_result() again on the same waiters.
-        self.loop.set_exception_handler(
-            lambda loop, context: self.fail(
-                f"unexpected exception: {context}")
-        )
-        waiter = self.loop.create_future()
-        transport, protocol = self.create_transport(waiter)
-
-        # Simulate a waiter registered via _wait() before the process exits.
-        exit_waiter = self.loop.create_future()
-        transport._exit_waiters.append(exit_waiter)
-
-        # _connect_pipes hasn't completed, so _pipes_connected is False.
-        self.assertFalse(transport._pipes_connected)
-
-        # Simulate process exit. _try_finish() will set the result on
-        # exit_waiter because _pipes_connected is False, and then schedule
-        # _call_connection_lost() because _pipes is empty (vacuously all
-        # disconnected). _call_connection_lost() must skip exit_waiter
-        # because it's already done.
-        transport._process_exited(6)
-        self.loop.run_until_complete(waiter)
-
-        self.assertEqual(exit_waiter.result(), 6)
-
-        transport.close()
-
 
 class SubprocessMixin:
 
@@ -435,6 +404,46 @@ async def len_message(message):
         self.assertEqual(output.rstrip(), b'3')
         self.assertEqual(exitcode, 0)
 
+    def test_wait_even_if_pipe_is_open(self):
+        # gh-119710: Process.wait() must return once the process exits even
+        # if its stdout pipe is inherited by a grandchild that keeps it open,
+        # so the pipe never reaches EOF. Otherwise wait() hangs forever
+        # despite the returncode being known.
+
+        async def run():
+            # The grandchild inherits the child's stdin and stdout pipes and
+            # keeps both open after the child is killed.  It writes "ready"
+            # so we know it has started, and exits once its stdin hits EOF.
+            code = textwrap.dedent("""\
+                import subprocess, sys
+                subprocess.run([sys.executable, "-c",
+                    "import sys; sys.stdout.write('ready');"
+                    " sys.stdout.flush(); sys.stdin.read()"])
+                """)
+
+            proc = await asyncio.create_subprocess_exec(
+                sys.executable, "-c", code,
+                stdin=subprocess.PIPE,
+                stdout=subprocess.PIPE,
+            )
+            try:
+                wait_proc = asyncio.create_task(proc.wait())
+                # Wait until the grandchild holds the inherited pipes; this
+                # also lets the wait() task register its waiter.
+                await proc.stdout.readexactly(5)
+                proc.kill()
+                returncode = await asyncio.wait_for(
+                    wait_proc, timeout=support.SHORT_TIMEOUT)
+                if sys.platform == 'win32':
+                    self.assertIsInstance(returncode, int)
+                else:
+                    self.assertEqual(-signal.SIGKILL, returncode)
+            finally:
+                proc.stdin.close()  # let the grandchild exit
+                await proc.stdout.read()
+
+        self.loop.run_until_complete(run())
+
     def test_empty_input(self):
 
         async def empty_input():

Misc/NEWS.d/next/Library/2026-06-11-10-00-00.gh-issue-119710.Qz7Kp2.rst

@@ -0,0 +1,4 @@
+Fix :mod:`asyncio` subprocess :meth:`~asyncio.subprocess.Process.wait`
+hanging when the process has exited but one of its pipes is kept open by an
+inherited child process (so the pipe never reaches EOF). ``wait()`` now
+returns as soon as the process exits, regardless of the pipes' state.