gh-103847: fix cancellation safety of asyncio.create_subprocess_exec (#140805)

Lib/asyncio/base_subprocess.py

@@ -26,6 +26,7 @@ class BaseSubprocessTransport(transports.SubprocessTransport):
         self._pending_calls = collections.deque()
         self._pipes = {}
         self._finished = False
+        self._pipes_connected = False
 
         if stdin == subprocess.PIPE:
             self._pipes[0] = None
@@ -213,6 +214,7 @@ class BaseSubprocessTransport(transports.SubprocessTransport):
         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:
@@ -256,6 +258,15 @@ class BaseSubprocessTransport(transports.SubprocessTransport):
         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.cancelled():
+                    waiter.set_result(self._returncode)
         if all(p is not None and p.disconnected
                for p in self._pipes.values()):
             self._finished = True

Lib/test/test_asyncio/test_subprocess.py

@@ -11,7 +11,7 @@ from asyncio import base_subprocess
 from asyncio import subprocess
 from test.test_asyncio import utils as test_utils
 from test import support
-from test.support import os_helper
+from test.support import os_helper, warnings_helper, gc_collect
 
 if not support.has_subprocess_support:
     raise unittest.SkipTest("test module requires subprocess")
@@ -879,6 +879,44 @@ class SubprocessMixin:
 
         self.loop.run_until_complete(main())
 
+    @warnings_helper.ignore_warnings(category=ResourceWarning)
+    def test_subprocess_read_pipe_cancelled(self):
+        async def main():
+            loop = asyncio.get_running_loop()
+            loop.connect_read_pipe = mock.AsyncMock(side_effect=asyncio.CancelledError)
+            with self.assertRaises(asyncio.CancelledError):
+                await asyncio.create_subprocess_exec(*PROGRAM_BLOCKED, stderr=asyncio.subprocess.PIPE)
+
+        asyncio.run(main())
+        gc_collect()
+
+    @warnings_helper.ignore_warnings(category=ResourceWarning)
+    def test_subprocess_write_pipe_cancelled(self):
+        async def main():
+            loop = asyncio.get_running_loop()
+            loop.connect_write_pipe = mock.AsyncMock(side_effect=asyncio.CancelledError)
+            with self.assertRaises(asyncio.CancelledError):
+                await asyncio.create_subprocess_exec(*PROGRAM_BLOCKED, stdin=asyncio.subprocess.PIPE)
+
+        asyncio.run(main())
+        gc_collect()
+
+    @warnings_helper.ignore_warnings(category=ResourceWarning)
+    def test_subprocess_read_write_pipe_cancelled(self):
+        async def main():
+            loop = asyncio.get_running_loop()
+            loop.connect_read_pipe = mock.AsyncMock(side_effect=asyncio.CancelledError)
+            loop.connect_write_pipe = mock.AsyncMock(side_effect=asyncio.CancelledError)
+            with self.assertRaises(asyncio.CancelledError):
+                await asyncio.create_subprocess_exec(
+                    *PROGRAM_BLOCKED,
+                    stdin=asyncio.subprocess.PIPE,
+                    stdout=asyncio.subprocess.PIPE,
+                    stderr=asyncio.subprocess.PIPE,
+                )
+
+        asyncio.run(main())
+        gc_collect()
 
 if sys.platform != 'win32':
     # Unix

Misc/NEWS.d/next/Library/2025-10-31-13-57-55.gh-issue-103847.VM7TnW.rst

@@ -0,0 +1 @@
+Fix hang when cancelling process created by :func:`asyncio.create_subprocess_exec` or :func:`asyncio.create_subprocess_shell`. Patch by Kumar Aditya.