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 4a0121168711aca15951712a7691468744d9ff88..e30f0e354dae74f3756fdf295c400dd8eadbc506 100644 (file)
--- a/Doc/library/threading.rst
+++ b/Doc/library/threading.rst
@@ -244,6 +244,12 @@ is that the entire Python program exits when only daemon threads are left.
 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.