From 62bfb2f291ba441abbac80d0a0853f147ebc9160 Mon Sep 17 00:00:00 2001
From: Irit Katriel <iritkatriel@yahoo.com>
Date: Fri, 7 Aug 2020 16:11:00 +0100
Subject: [PATCH 1/2] bpo-41503: Race between setTarget and flush in
 logging.handlers.MemoryHandler

---
 Lib/logging/handlers.py  |  6 +++++-
 Lib/test/test_logging.py | 21 +++++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/Lib/logging/handlers.py b/Lib/logging/handlers.py
index 4a120e9f1ec48f..867ef4ebc7600a 100644
--- a/Lib/logging/handlers.py
+++ b/Lib/logging/handlers.py
@@ -1324,7 +1324,11 @@ def setTarget(self, target):
         """
         Set the target handler for this handler.
         """
-        self.target = target
+        self.acquire()
+        try:
+            self.target = target
+        finally:
+            self.release()
 
     def flush(self):
         """
diff --git a/Lib/test/test_logging.py b/Lib/test/test_logging.py
index eb5b926908a192..d8b3727eb11851 100644
--- a/Lib/test/test_logging.py
+++ b/Lib/test/test_logging.py
@@ -1160,6 +1160,27 @@ def test_flush_on_close(self):
         # assert that no new lines have been added
         self.assert_log_lines(lines)  # no change
 
+    def test_race_between_set_target_and_flush(self):
+        class MockRaceConditionHandler:
+            def __init__(self, mem_hdlr):
+                self.mem_hdlr = mem_hdlr
+
+            def removeTarget(self):
+                self.mem_hdlr.setTarget(None)
+
+            def handle(self, msg):
+                t = threading.Thread(target=self.removeTarget)
+                t.daemon = True
+                t.start()
+
+        target = MockRaceConditionHandler(self.mem_hdlr)
+        self.mem_hdlr.setTarget(target)
+
+        for _ in range(10):
+            time.sleep(0.005)
+            self.mem_logger.info("not flushed")
+            self.mem_logger.warning("flushed")
+
 
 class ExceptionFormatter(logging.Formatter):
     """A special exception formatter."""

From e3884b0ab78e9846225c85991ae45a8de3a9b2cf Mon Sep 17 00:00:00 2001
From: "blurb-it[bot]" <43283697+blurb-it[bot]@users.noreply.github.com>
Date: Fri, 7 Aug 2020 15:18:17 +0000
Subject: [PATCH 2/2] =?UTF-8?q?=F0=9F=93=9C=F0=9F=A4=96=20Added=20by=20blu?=
 =?UTF-8?q?rb=5Fit.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../NEWS.d/next/Library/2020-08-07-15-18-16.bpo-41503.IYftcu.rst | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 Misc/NEWS.d/next/Library/2020-08-07-15-18-16.bpo-41503.IYftcu.rst

diff --git a/Misc/NEWS.d/next/Library/2020-08-07-15-18-16.bpo-41503.IYftcu.rst b/Misc/NEWS.d/next/Library/2020-08-07-15-18-16.bpo-41503.IYftcu.rst
new file mode 100644
index 00000000000000..c34996d881937b
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-08-07-15-18-16.bpo-41503.IYftcu.rst
@@ -0,0 +1 @@
+Fixed a race between setTarget and flush in logging.handlers.MemoryHandler.
\ No newline at end of file