Add news entry

Author: giampaolo

Doc/library/subprocess.rst

@@ -807,7 +807,8 @@ Instances of the :class:`Popen` class have the following methods:
       waits for process termination when available:
 
       - Linux ≥5.3 uses :func:`os.pidfd_open` + :func:`select.poll`
-      - macOS and other BSD variants use :func:`select.kqueue`
+      - macOS and other BSD variants use :func:`select.kqueue` +
+        ``KQ_FILTER_PROC`` + ``KQ_NOTE_EXIT``
       - Windows uses ``WaitForSingleObject``
 
       If none of these mechanisms are available, the function falls back to a
@@ -819,7 +820,8 @@ Instances of the :class:`Popen` class have the following methods:
       *timeout* was added.
 
    .. versionchanged:: 3.15
-      use efficient event-driven implementation on Linux >= 5.3 and macOS / BSD.
+      if *timeout* is not ``None``, use efficient event-driven implementation
+      on Linux >= 5.3 and macOS / BSD.
 
 .. method:: Popen.communicate(input=None, timeout=None)
 

Misc/NEWS.d/next/Library/2026-01-19-16-45-16.gh-issue-83069.0TaeH9.rst

@@ -0,0 +1,12 @@
+:meth:`subprocess.Popen.wait`: when ``timeout`` is not ``None``, an efficient
+event-driven mechanism now waits for process termination, if available:
+
+- Linux ≥5.3 uses :func:`os.pidfd_open` + :func:`select.poll`
+- macOS and other BSD variants use :func:`select.kqueue` + ``KQ_FILTER_PROC`` +
+  ``KQ_NOTE_EXIT``
+- Windows keep using ``WaitForSingleObject`` (unchanged)
+
+If none of these mechanisms are available, the function falls back to the
+traditional busy loop (non-blocking call and short sleeps).
+
+Patch by Giampaolo Rodola.