bpo-37380: subprocess: don't use _active on win (GH-14360) (GH-15706)

As noted by @eryksun in [1] and [2], using _cleanup and _active(in
__del__) is not necessary on Windows, since:

> Unlike Unix, a process in Windows doesn't have to be waited on by
> its parent to avoid a zombie. Keeping the handle open will actually
> create a zombie until the next _cleanup() call, which may be never
> if Popen() isn't called again.

This patch simply defines `subprocess._active` as `None`, for which we already
have the proper logic in place in `subprocess.Popen.__del__`, that prevents it
from trying to append the process to the `_active`. This patch also defines
`subprocess._cleanup` as a noop for Windows.

[1] https://bugs.python.org/issue37380GH-msg346333
[2] https://bugs.python.org/issue36067GH-msg336262

Signed-off-by: Ruslan Kuprieiev <ruslan@iterative.ai>
(cherry picked from commit 042821ae3cf537e01963c9ec85d1a454d921e826)

Co-authored-by: Ruslan Kuprieiev <kupruser@gmail.com>

1 files changed, 25 insertions, 9 deletions

diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index 8419061..41e6a09 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -59,10 +59,14 @@ class BaseTestCase(unittest.TestCase):
         support.reap_children()
 
     def tearDown(self):
-        for inst in subprocess._active:
-            inst.wait()
-        subprocess._cleanup()
-        self.assertFalse(subprocess._active, "subprocess._active not empty")
+        if not mswindows:
+            # subprocess._active is not used on Windows and is set to None.
+            for inst in subprocess._active:
+                inst.wait()
+            subprocess._cleanup()
+            self.assertFalse(
+                subprocess._active, "subprocess._active not empty"
+            )
         self.doCleanups()
         support.reap_children()
 
@@ -2622,8 +2626,12 @@ class POSIXProcessTestCase(BaseTestCase):
         with support.check_warnings(('', ResourceWarning)):
             p = None
 
-        # check that p is in the active processes list
-        self.assertIn(ident, [id(o) for o in subprocess._active])
+        if mswindows:
+            # subprocess._active is not used on Windows and is set to None.
+            self.assertIsNone(subprocess._active)
+        else:
+            # check that p is in the active processes list
+            self.assertIn(ident, [id(o) for o in subprocess._active])
 
     def test_leak_fast_process_del_killed(self):
         # Issue #12650: on Unix, if Popen.__del__() was called before the
@@ -2644,8 +2652,12 @@ class POSIXProcessTestCase(BaseTestCase):
             p = None
 
         os.kill(pid, signal.SIGKILL)
-        # check that p is in the active processes list
-        self.assertIn(ident, [id(o) for o in subprocess._active])
+        if mswindows:
+            # subprocess._active is not used on Windows and is set to None.
+            self.assertIsNone(subprocess._active)
+        else:
+            # check that p is in the active processes list
+            self.assertIn(ident, [id(o) for o in subprocess._active])
 
         # let some time for the process to exit, and create a new Popen: this
         # should trigger the wait() of p
@@ -2657,7 +2669,11 @@ class POSIXProcessTestCase(BaseTestCase):
                 pass
         # p should have been wait()ed on, and removed from the _active list
         self.assertRaises(OSError, os.waitpid, pid, 0)
-        self.assertNotIn(ident, [id(o) for o in subprocess._active])
+        if mswindows:
+            # subprocess._active is not used on Windows and is set to None.
+            self.assertIsNone(subprocess._active)
+        else:
+            self.assertNotIn(ident, [id(o) for o in subprocess._active])
 
     def test_close_fds_after_preexec(self):
         fd_status = support.findfile("fd_status.py", subdir="subprocessdata")