bpo-35721: Close socket pair if Popen in _UnixSubprocessTransport fails (GH-11553)

This slightly expands an existing test case `test_popen_error` to trigger a `ResourceWarning` and fixes it. https://bugs.python.org/issue35721

Author: niklasf

Lib/asyncio/unix_events.py

@@ -757,12 +757,18 @@ def _start(self, args, shell, stdin, stdout, stderr, bufsize, **kwargs):
  # other end). Notably this is needed on AIX, and works
  # just fine on other platforms.
  stdin, stdin_w = socket.socketpair()
- self._proc = subprocess.Popen(
- args, shell=shell, stdin=stdin, stdout=stdout, stderr=stderr,
- universal_newlines=False, bufsize=bufsize, **kwargs)
- if stdin_w is not None:
- stdin.close()
- self._proc.stdin = open(stdin_w.detach(), 'wb', buffering=bufsize)
+ try:
+ self._proc = subprocess.Popen(
+ args, shell=shell, stdin=stdin, stdout=stdout, stderr=stderr,
+ universal_newlines=False, bufsize=bufsize, **kwargs)
+ if stdin_w is not None:
+ stdin.close()
+ self._proc.stdin = open(stdin_w.detach(), 'wb', buffering=bufsize)
+ stdin_w = None
+ finally:
+ if stdin_w is not None:
+ stdin.close()
+ stdin_w.close()
 
 
 class AbstractChildWatcher:

Lib/test/test_asyncio/test_subprocess.py

@@ -468,9 +468,7 @@ async def kill_running():
  isinstance(self, SubprocessFastWatcherTests)):
  asyncio.get_child_watcher()._callbacks.clear()
 
- def test_popen_error(self):
- # Issue #24763: check that the subprocess transport is closed
- # when BaseSubprocessTransport fails
+ def _test_popen_error(self, stdin):
  if sys.platform == 'win32':
  target = 'asyncio.windows_utils.Popen'
  else:
@@ -480,12 +478,23 @@ def test_popen_error(self):
  popen.side_effect = exc
 
  create = asyncio.create_subprocess_exec(sys.executable, '-c',
- 'pass', loop=self.loop)
+ 'pass', stdin=stdin,
+ loop=self.loop)
  with warnings.catch_warnings(record=True) as warns:
  with self.assertRaises(exc):
  self.loop.run_until_complete(create)
  self.assertEqual(warns, [])
 
+ def test_popen_error(self):
+ # Issue #24763: check that the subprocess transport is closed
+ # when BaseSubprocessTransport fails
+ self._test_popen_error(stdin=None)
+
+ def test_popen_error_with_stdin_pipe(self):
+ # Issue #35721: check that newly created socket pair is closed when
+ # Popen fails
+ self._test_popen_error(stdin=subprocess.PIPE)
+
  def test_read_stdout_after_process_exit(self):
 
  async def execute():

Misc/ACKS

@@ -486,6 +486,7 @@ Florian Festi
 John Feuerstein
 Carl Feynman
 Vincent Fiack
+Niklas Fiekas
 Anastasia Filatova
 Tomer Filiba
 Segev Finer

Misc/NEWS.d/next/Library/2019-01-18-16-23-00.bpo-35721.d8djAJ.rst

@@ -0,0 +1,3 @@
+Fix :meth:`asyncio.SelectorEventLoop.subprocess_exec()` leaks file descriptors
+if ``Popen`` fails and called with ``stdin=subprocess.PIPE``.
+Patch by Niklas Fiekas.