https://github.com/python/cpython/commit/526d7a8bb47bd8ff58c829c30384cd70cc5d0747 commit: 526d7a8bb47bd8ff58c829c30384cd70cc5d0747 branch: main author: Artur Jamro <[email protected]> committer: gpshead <[email protected]> date: 2025-11-28T18:04:52-08:00 summary:
gh-141473: Fix subprocess.Popen.communicate to send input to stdin upon a subsequent post-timeout call (GH-141477) * gh-141473: Fix subprocess.Popen.communicate to send input to stdin * Docs: Clarify that `input` is one time only on `communicate()` * NEWS entry * Add a regression test. --------- Co-authored-by: Gregory P. Smith <[email protected]> files: A Misc/NEWS.d/next/Library/2025-11-27-20-16-38.gh-issue-141473.Wq4xVN.rst M Doc/library/subprocess.rst M Lib/subprocess.py M Lib/test/test_subprocess.py diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst index 1aade881745f21..43da804b62beb1 100644 --- a/Doc/library/subprocess.rst +++ b/Doc/library/subprocess.rst @@ -831,7 +831,9 @@ Instances of the :class:`Popen` class have the following methods: If the process does not terminate after *timeout* seconds, a :exc:`TimeoutExpired` exception will be raised. Catching this exception and - retrying communication will not lose any output. + retrying communication will not lose any output. Supplying *input* to a + subsequent post-timeout :meth:`communicate` call is in undefined behavior + and may become an error in the future. The child process is not killed if the timeout expires, so in order to cleanup properly a well-behaved application should kill the child process and diff --git a/Lib/subprocess.py b/Lib/subprocess.py index 79251bd5310223..4955f77b60381f 100644 --- a/Lib/subprocess.py +++ b/Lib/subprocess.py @@ -2105,7 +2105,7 @@ def _communicate(self, input, endtime, orig_timeout): input_view = memoryview(self._input) with _PopenSelector() as selector: - if self.stdin and input: + if self.stdin and not self.stdin.closed and self._input: selector.register(self.stdin, selectors.EVENT_WRITE) if self.stdout and not self.stdout.closed: selector.register(self.stdout, selectors.EVENT_READ) diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py index f0e350c71f60ea..9792d7c8983cd3 100644 --- a/Lib/test/test_subprocess.py +++ b/Lib/test/test_subprocess.py @@ -1643,6 +1643,40 @@ def test_wait_negative_timeout(self): self.assertEqual(proc.wait(), 0) + def test_post_timeout_communicate_sends_input(self): + """GH-141473 regression test; the stdin pipe must close""" + with subprocess.Popen( + [sys.executable, "-uc", """\ +import sys +while c := sys.stdin.read(512): + sys.stdout.write(c) +print() +"""], + stdin=subprocess.PIPE, + stdout=subprocess.PIPE, + stderr=subprocess.PIPE, + text=True, + ) as proc: + try: + data = f"spam{'#'*4096}beans" + proc.communicate( + input=data, + timeout=0, + ) + except subprocess.TimeoutExpired as exc: + pass + # Prior to the bugfix, this would hang as the stdin + # pipe to the child had not been closed. + try: + stdout, stderr = proc.communicate(timeout=15) + except subprocess.TimeoutExpired as exc: + self.fail("communicate() hung waiting on child process that should have seen its stdin pipe close and exit") + self.assertEqual( + proc.returncode, 0, + msg=f"STDERR:\n{stderr}\nSTDOUT:\n{stdout}") + self.assertStartsWith(stdout, "spam") + self.assertIn("beans", stdout) + class RunFuncTestCase(BaseTestCase): def run_python(self, code, **kwargs): diff --git a/Misc/NEWS.d/next/Library/2025-11-27-20-16-38.gh-issue-141473.Wq4xVN.rst b/Misc/NEWS.d/next/Library/2025-11-27-20-16-38.gh-issue-141473.Wq4xVN.rst new file mode 100644 index 00000000000000..f6aa592cefda35 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2025-11-27-20-16-38.gh-issue-141473.Wq4xVN.rst @@ -0,0 +1,4 @@ +When :meth:`subprocess.Popen.communicate` was called with *input* and a +*timeout* and is called for a second time after a +:exc:`~subprocess.TimeoutExpired` exception before the process has died, it +should no longer hang. _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
