[Python-checkins] bpo-38356: Fix ThreadedChildWatcher thread leak in test_asyncio (GH-16552)

[Miss Islington (bot)]

https://github.com/python/cpython/commit/0ca7cc7fc0518c24dc9b78c38418e6064e64f148
commit: 0ca7cc7fc0518c24dc9b78c38418e6064e64f148
branch: master
author: Kyle Stanley <aeros167 at gmail.com>
committer: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
date: 2020-01-12T03:02:50-08:00
summary:

bpo-38356: Fix ThreadedChildWatcher thread leak in test_asyncio (GH-16552)



Motivation for this PR (comment from @vstinner in bpo issue):
```
Warning seen o AMD64 Ubuntu Shared 3.x buildbot:
https://buildbot.python.org/all/#/builders/141/builds/2593

test_devnull_output (test.test_a=syncio.test_subprocess.SubprocessThreadedWatcherTests) ...
Warning -- threading_cleanup() failed to cleanup 1 threads (count: 1, dangling: 2)
```
The following implementation details for the new method are TBD:

1) Public vs private

2) Inclusion in `close()`

3) Name

4) Coroutine vs subroutine method

5) *timeout* parameter

If it's a private method, 3, 4, and 5 are significantly less important.

I started with the most minimal implementation that fixes the dangling threads without modifying the regression tests, which I think is particularly important. I typically try to avoid directly modifying existing tests as much as possible unless it's necessary to do so. However, I am open to changing any part of this.


https://bugs.python.org/issue38356

files:
M Lib/asyncio/unix_events.py

diff --git a/Lib/asyncio/unix_events.py b/Lib/asyncio/unix_events.py
index 28fb491864517..19d713545e4cd 100644
--- a/Lib/asyncio/unix_events.py
+++ b/Lib/asyncio/unix_events.py
@@ -1344,7 +1344,14 @@ def is_active(self):
         return True
 
     def close(self):
-        pass
+        self._join_threads()
+
+    def _join_threads(self):
+        """Internal: Join all non-daemon threads"""
+        threads = [thread for thread in list(self._threads.values())
+                   if thread.is_alive() and not thread.daemon]
+        for thread in threads:
+            thread.join()
 
     def __enter__(self):
         return self