Nov 21, 2020 · May 8, 2020 · Nov 21, 2020
diff --git a/Lib/subprocess.py b/Lib/subprocess.py
            # 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
        # 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
 Fix time-of-check/time-of-action issue in subprocess.Popen.send_signal.
Original file line number	Diff line number	Diff line change
Expand Up		@@ -2061,7 +2061,11 @@ def send_signal(self, sig):
		# 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
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -3145,6 +3145,19 @@ def test_send_signal_race(self):
		# 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)'],
Expand Down
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Fix time-of-check/time-of-action issue in subprocess.Popen.send_signal.