gh-154137: Check for Windows handle leaks in regrtest

[vstinner]

Add handle_count() to test.support.os_helper.

• Issue: test.regrtest: detect leak of Windows handles #154137

[vstinner]

I found a leak when running tests on Windows using python -m test -R 3:3 -j0 -r:

test.test_concurrent_futures.test_process_pool leaked [24, 24, 24] handles, sum=72

I can reproduce at least one of these leaks by running test_force_shutdown_workers():

C:> python -m test test_concurrent_futures.test_process_pool -R 3:3 -m test_force_shutdown_workers   
...
test_concurrent_futures.test_process_pool leaked [4, 4, 4] handles, sum=12
...

[vstinner]

test_socket leaks 1 handle:

vstinner@WIN C:\victor\python\main>python -m test -R 3:3 test_socket     
...
test_socket leaked [1, 1, 1] handles, sum=3
...

[vstinner]

TODO: Update test_getfinalpathname_handles() of Lib/test/test_os/test_windows.py to reuse support.handle_count().

[vstinner]

test_socket leaks 1 handle

I cannot identify the leaking test by running python -m test.bisect_cmd, so I'm not sure that it's a real leak.

[vstinner]

!buildbot AMD64 Windows11 Refleaks PR

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @vstinner for commit 37c29f3 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F154140%2Fmerge

The command will test the builders whose names match following regular expression: AMD64 Windows11 Refleaks PR

The builders matched are:

• AMD64 Windows11 Refleaks PR

[vstinner]

Ah, test_pathlib fails on Windows. I will fix later.

First, I'm waiting for Windows11 Refleaks buildbot report.

[vstinner]

Oh, it seems like test_multiprocessing_spawn.test_processes also leaks:

test.test_multiprocessing_spawn.test_processes leaked [36, 36, 36] handles, sum=108

[vstinner]

Aaaand last but not least:

test_winapi leaked [8482, 8482, 8482] handles, sum=25446

[vstinner]

!buildbot AMD64 Windows11 Refleaks PR

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @vstinner for commit e66fb14 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F154140%2Fmerge

The command will test the builders whose names match following regular expression: AMD64 Windows11 Refleaks PR

The builders matched are:

• AMD64 Windows11 Refleaks PR

[vstinner]

TODO: Update test_getfinalpathname_handles() of Lib/test/test_os/test_windows.py to reuse support.handle_count().

Done.

test_winapi leaked [8482, 8482, 8482] handles, sum=25446

Fixed by PR gh-154201.

test.test_multiprocessing_spawn.test_processes leaked [36, 36, 36] handles, sum=108

I created issue gh-154208 to investigate this leak.