From 3d7dfbc1c19280dd19693d8d8e0574590c0c1bee Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Filipe=20La=C3=ADns?= <lains@archlinux.org>
Date: Fri, 8 May 2020 22:18:05 +0100
Subject: [PATCH 1/2] bpo-40550: fix time-of-check/time-of-action issue in
 multiprocessing
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Signed-off-by: Filipe Laíns <lains@archlinux.org>
---
 Lib/subprocess.py                                   |  8 +++++++-
 Lib/test/test_subprocess.py                         | 13 +++++++++++++
 .../2020-05-08-21-30-54.bpo-40550.i7GWkb.rst        |  1 +
 3 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2020-05-08-21-30-54.bpo-40550.i7GWkb.rst

diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 13600c28cf7117..b40d1c38ff09d3 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -2061,7 +2061,13 @@ 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 as e:
+                # supress the process not found error in case the race
+                # condition happens, see bpo-40550
+                if e.errno != errno.ESRCH:
+                    raise e
 
         def terminate(self):
             """Terminate the process with SIGTERM
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index aced87694cf7b6..3a63869231a3bd 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -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)'],
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 00000000000000..b0f3f03c34bbc5
--- /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.

From 1605031b9a5eeb922feb7d76ebfad583a9637a96 Mon Sep 17 00:00:00 2001
From: "Gregory P. Smith" <greg@krypto.org>
Date: Sat, 21 Nov 2020 00:48:42 -0800
Subject: [PATCH 2/2] Remove a redundant check of errno.

The ProcessLookupError already means errno == ESRCH.
---
 Lib/subprocess.py | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index b40d1c38ff09d3..f1d829a6f1724e 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -2063,11 +2063,9 @@ def send_signal(self, sig):
             # and the kill() call.
             try:
                 os.kill(self.pid, sig)
-            except ProcessLookupError as e:
-                # supress the process not found error in case the race
-                # condition happens, see bpo-40550
-                if e.errno != errno.ESRCH:
-                    raise e
+            except ProcessLookupError:
+                # Supress the race condition error; bpo-40550.
+                pass
 
         def terminate(self):
             """Terminate the process with SIGTERM