`build_docs` fails with `[Makefile:42: html] Hangup`

[datumbox]

🐛 Describe the bug

The build_docs CI job fails on the latest main with:

make: *** [Makefile:42: html] Hangup

The job later times out on the CI once the 10-minute time limit is exhausted.

Versions

Started appearing on 20221031

cc @seemethere

[pmeier]

#6598 is the offender @bjuncek @jdsgomes. I'm not sure yet why, but after that commit, building with multiple processes hangs. We do that by default with the -j flag:

vision/docs/Makefile

Line 9 in d95fbaf

SPHINXOPTS = -W -j auto $(EXAMPLES_PATTERN_OPTS)

Removing the multiprocessing like I did in #6884, resolves the issue.

[NicolasHug]

There might be something fishy going on in the VideoReader then. Could we try to use it in a multi-processing setting, e.g. with DataLoader(num_workers>1), and see if the lock happens?