regrtest has been modified in bpo-38502 to use setsid() when using multiprocessing mode (-jN command line option).

Problem: David Bolen identified that test_pty started to fail on his bolen-ubuntu worker (Ubuntu 18.04.3) since my commit ecb035cd14c11521276343397151929a94018a22.

https://buildbot.python.org/all/#/builders/141/builds/2679

0:19:05 load avg: 1.81 [234/419/1] test_pty crashed (Exit code -1) -- running: test_unicodedata (55.5 sec)

I can reproduce the issue locally:

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$ ./python -m test -j2 test_pty -v
== CPython 3.9.0a0 (heads/urlparse_ipv6:cc733a8cb6, Oct 21 2019, 11:34:36) [GCC 9.2.1 20190827 (Red Hat 9.2.1-1)]
== Linux-5.2.18-200.fc30.x86_64-x86_64-with-glibc2.29 little-endian
== cwd: /home/vstinner/python/master/build/test_python_20242
== CPU count: 8
== encodings: locale=UTF-8, FS=utf-8
0:00:00 load avg: 0.70 Run tests in parallel using 2 child processes
0:00:00 load avg: 0.70 [1/1/1] test_pty crashed (Exit code -1)
test_basic (test.test_pty.PtyTest) ...

== Tests result: FAILURE ==

1 test failed:
    test_pty

Total duration: 383 ms
Tests result: FAILURE
---

It's surprising that there is no output!

I would prefer to keep process groups in regrtest, it's really helpful to be able to kill all processes spawned by a test worker process.

I'm not sure how/why PTY depends is incompatible with setsid().