bpo-38630: Fix subprocess.Popen.send_signal() race condition (GH-16984)
On Unix, subprocess.Popen.send_signal() now polls the process status.
Polling reduces the risk of sending a signal to the wrong process if
the process completed, the Popen.returncode attribute is still None,
and the pid has been reassigned (recycled) to a new different
process.
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index 2073fd1..f1fb934 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -3120,6 +3120,31 @@
self.assertEqual(returncode, -3)
+ def test_send_signal_race(self):
+ # bpo-38630: send_signal() must poll the process exit status to reduce
+ # the risk of sending the signal to the wrong process.
+ proc = subprocess.Popen(ZERO_RETURN_CMD)
+
+ # wait until the process completes without using the Popen APIs.
+ pid, status = os.waitpid(proc.pid, 0)
+ self.assertEqual(pid, proc.pid)
+ self.assertTrue(os.WIFEXITED(status), status)
+ self.assertEqual(os.WEXITSTATUS(status), 0)
+
+ # returncode is still None but the process completed.
+ self.assertIsNone(proc.returncode)
+
+ with mock.patch("os.kill") as mock_kill:
+ proc.send_signal(signal.SIGTERM)
+
+ # send_signal() didn't call os.kill() since the process already
+ # completed.
+ mock_kill.assert_not_called()
+
+ # Don't check the returncode value: the test reads the exit status,
+ # so Popen failed to read it and uses a default returncode instead.
+ self.assertIsNotNone(proc.returncode)
+
@unittest.skipUnless(mswindows, "Windows specific tests")
class Win32ProcessTestCase(BaseTestCase):