On POSIX-compliant systems, :func:`!multiprocessing.util.get_temp_dir` now
ignores :envvar:`TMPDIR` (and similar environment variables) if the path
length of ``AF_UNIX`` socket files exceeds the platform-specific maximum
length when using the :ref:`forkserver
<multiprocessing-start-method-forkserver>` start method. Patch by Bénédikt
Tran.
