bpo-35621: Support running subprocesses in asyncio when loop is executed in non-main thread (GH-14344)

1 files changed, 17 insertions, 9 deletions

diff --git a/Doc/library/asyncio-subprocess.rst b/Doc/library/asyncio-subprocess.rst
index 00dc66c48b..444fb6361b 100644
--- a/Doc/library/asyncio-subprocess.rst
+++ b/Doc/library/asyncio-subprocess.rst
@@ -293,18 +293,26 @@ their completion.
 Subprocess and Threads
 ----------------------
 
-Standard asyncio event loop supports running subprocesses from
-different threads, but there are limitations:
+Standard asyncio event loop supports running subprocesses from different threads by
+default.
 
-* An event loop must run in the main thread.
+On Windows subprocesses are provided by :class:`ProactorEventLoop` only (default),
+:class:`SelectorEventLoop` has no subprocess support.
 
-* The child watcher must be instantiated in the main thread
-  before executing subprocesses from other threads. Call the
-  :func:`get_child_watcher` function in the main thread to instantiate
-  the child watcher.
+On UNIX *child watchers* are used for subprocess finish waiting, see
+:ref:`asyncio-watchers` for more info.
 
-Note that alternative event loop implementations might not share
-the above limitations; please refer to their documentation.
+
+.. versionchanged:: 3.8
+
+   UNIX switched to use :class:`ThreadedChildWatcher` for spawning subprocesses from
+   different threads without any limitation.
+
+   Spawning a subprocess with *inactive* current child watcher raises
+   :exc:`RuntimeError`.
+
+Note that alternative event loop implementations might have own limitations;
+please refer to their documentation.
 
 .. seealso::