Issue #17208: add a note about the termination behaviour of daemon threads.
diff --git a/Doc/library/threading.rst b/Doc/library/threading.rst
index 4a01211..e30f0e3 100644
--- a/Doc/library/threading.rst
+++ b/Doc/library/threading.rst
@@ -244,6 +244,12 @@
The initial value is inherited from the creating thread. The flag can be
set through the :attr:`~Thread.daemon` property.
+.. note::
+ Daemon threads are abruptly stopped at shutdown. Their resources (such
+ as open files, database transactions, etc.) may not be released properly.
+ If you want your threads to stop gracefully, make them non-daemonic and
+ use a suitable signalling mechanism such as an :class:`Event`.
+
There is a "main thread" object; this corresponds to the initial thread of
control in the Python program. It is not a daemon thread.