[issue31234] Make support.threading_cleanup() stricter

[STINNER Victor]

New submission from STINNER Victor:

Currently, support.threading_cleanup() waits 1 second before emitting a warning about threads running in the background. I propose to emit immediately the warning to be able to catch bugs quicker, bugs like bpo-31233 or bpo-30830.

The problem is that currently, 12 test files still leak threads:
---
12 tests altered the execution environment:
    test_asyncio test_concurrent_futures test_fork1 test_httpservers
    test_logging test_pydoc test_ssl test_thread test_threaded_import
    test_threading test_wait3 test_xmlrpc
---

Since threading_cleanup() warnings now mark tests as failed, we should first fix these tests before being able to make support.threading_cleanup() stricter.

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components: Tests
messages: 300519
nosy: haypo
priority: normal
severity: normal
status: open
title: Make support.threading_cleanup() stricter
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue31234>
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