bpo-40550: Fix time-of-check/time-of-action issue in subprocess.Popen.send_signal. (GH-20010)
send_signal() now swallows the exception if the process it thought was still alive winds up not to exist anymore (always a plausible race condition despite the checks).
Co-authored-by: Gregory P. Smith <greg@krypto.org>
diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 6a6c2fc..e259dc3 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -2078,7 +2078,11 @@
# The race condition can still happen if the race condition
# described above happens between the returncode test
# and the kill() call.
- os.kill(self.pid, sig)
+ try:
+ os.kill(self.pid, sig)
+ except ProcessLookupError:
+ # Supress the race condition error; bpo-40550.
+ pass
def terminate(self):
"""Terminate the process with SIGTERM
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index e25474a..2a4c475 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -3229,6 +3229,19 @@
# so Popen failed to read it and uses a default returncode instead.
self.assertIsNotNone(proc.returncode)
+ def test_send_signal_race2(self):
+ # bpo-40550: the process might exist between the returncode check and
+ # the kill operation
+ p = subprocess.Popen([sys.executable, '-c', 'exit(1)'])
+
+ # wait for process to exit
+ while not p.returncode:
+ p.poll()
+
+ with mock.patch.object(p, 'poll', new=lambda: None):
+ p.returncode = None
+ p.send_signal(signal.SIGTERM)
+
def test_communicate_repeated_call_after_stdout_close(self):
proc = subprocess.Popen([sys.executable, '-c',
'import os, time; os.close(1), time.sleep(2)'],
diff --git a/Misc/NEWS.d/next/Library/2020-05-08-21-30-54.bpo-40550.i7GWkb.rst b/Misc/NEWS.d/next/Library/2020-05-08-21-30-54.bpo-40550.i7GWkb.rst
new file mode 100644
index 0000000..b0f3f03
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-05-08-21-30-54.bpo-40550.i7GWkb.rst
@@ -0,0 +1 @@
+Fix time-of-check/time-of-action issue in subprocess.Popen.send_signal.