[tlbuild] Intermittent W32TeX xdvipdfmx crashes

[Tim Eyre]

As per my recent post (
https://tug.org/pipermail/dvipdfmx/2021-January/000200.html) to the
dvipdfmx mailing list, there seems to be a glitch in the W32TeX version of
xdvipdfmx. Here is a minimal example:

\font\Korean="Batang" at 10pt
\newcount\CrashCount
\CrashCount=1
\loop\ifnum\CrashCount<4000
    X {\Korean 서울} X
  \advance\CrashCount by1
  \repeat
\bye

The crash is intermittent, so I use the following batch job to drive the
repro:

@echo off
xetex -no-pdf test.tex
:LOOPSTART
xdvipdfmx test.xdv
if "%ERRORLEVEL%"=="0" goto LOOPSTART
echo Failed with error %ERRORLEVEL%

Every few runs I get

Failed with error -1073741819

-1073741819 = 0xC0000005 = Access Violation

This happens with the very latest xetex+dvipdfmx builds from
http://w32tex.org/ and also in my TeXLive 2020 install. With kind help from
Hirata-san on the dvipdfmx mailing list, we determined that this crash
doesn't happen with Hirata-san's local build of xdvipdfmx. It also didn't
happen before I migrated from TeXLive 2013. Therefore it seems that there
is a glitch in the W32TeX/TeXLive 2020 xdvipdfmx build.

If this is something that the TeXLive maintainers would like to address
then I am very willing to help. Maybe the above test could be included in
the TeXLive 2021 test suite?

With Hirata-san's build and a retry workaround I've put in my code, this
issue isn't causing me any problems. I'm just reporting it out of a sense
of duty.

Tim
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