From 13ff396c019d548ba181cf22c6f39309a300723c Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Mon, 12 Oct 2020 00:37:20 +0200
Subject: [PATCH] bpo-41739: Fix
 test_logging.test_race_between_set_target_and_flush() (GH-22655)

The test now waits until all threads complete to avoid leaking
running threads.

Also, use regular threads rather than daemon threads.
---
 Lib/test/test_logging.py                      | 21 ++++++++++++-------
 .../2020-10-12-00-11-47.bpo-41739.wSCc4K.rst  |  2 ++
 2 files changed, 15 insertions(+), 8 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Tests/2020-10-12-00-11-47.bpo-41739.wSCc4K.rst

diff --git a/Lib/test/test_logging.py b/Lib/test/test_logging.py
index 4cd8c7e25da..7c98e19b740 100644
--- a/Lib/test/test_logging.py
+++ b/Lib/test/test_logging.py
@@ -1164,22 +1164,27 @@ class MemoryHandlerTest(BaseTest):
         class MockRaceConditionHandler:
             def __init__(self, mem_hdlr):
                 self.mem_hdlr = mem_hdlr
+                self.threads = []
 
             def removeTarget(self):
                 self.mem_hdlr.setTarget(None)
 
             def handle(self, msg):
-                t = threading.Thread(target=self.removeTarget)
-                t.daemon = True
-                t.start()
+                thread = threading.Thread(target=self.removeTarget)
+                self.threads.append(thread)
+                thread.start()
 
         target = MockRaceConditionHandler(self.mem_hdlr)
-        self.mem_hdlr.setTarget(target)
+        try:
+            self.mem_hdlr.setTarget(target)
 
-        for _ in range(10):
-            time.sleep(0.005)
-            self.mem_logger.info("not flushed")
-            self.mem_logger.warning("flushed")
+            for _ in range(10):
+                time.sleep(0.005)
+                self.mem_logger.info("not flushed")
+                self.mem_logger.warning("flushed")
+        finally:
+            for thread in target.threads:
+                threading_helper.join_thread(thread)
 
 
 class ExceptionFormatter(logging.Formatter):
diff --git a/Misc/NEWS.d/next/Tests/2020-10-12-00-11-47.bpo-41739.wSCc4K.rst b/Misc/NEWS.d/next/Tests/2020-10-12-00-11-47.bpo-41739.wSCc4K.rst
new file mode 100644
index 00000000000..7aee2b94444
--- /dev/null
+++ b/Misc/NEWS.d/next/Tests/2020-10-12-00-11-47.bpo-41739.wSCc4K.rst
@@ -0,0 +1,2 @@
+Fix test_logging.test_race_between_set_target_and_flush(): the test now
+waits until all threads complete to avoid leaking running threads.