Bug#981201: xvfb-run: makes tests flaky if multiple clients connect without -noreset

[Simon McVittie <smcv@debian.org>]

Control: retitle -1 xvfb-run: makes tests flaky if multiple clients connect without -noreset

On Wed, 27 Jan 2021 at 19:50:58 +0100, Sebastien Bacher wrote:
> Le 27/01/2021 à 18:46, Marcin Owsiany a écrit :
> > My concern here is that we're effectively papering over some issue in
> > xvfb, in multiple places rather than fixing it once properly at the
> > source.
> 
> Ideally that wouldn't be needed indeed, fixing it in xvfb if possible
> would be best.

I've retitled #981201 to try to make it more obvious that #981201 is
about the situation where a test connects more than one client to the
X server, passing through a state where 0 clients are connected in the
process, and does not pass -noreset to xvfb-run. I think race conditions
in starting up Xvfb for the first time (#1095028) should be considered
out-of-scope for this particular bug report.

The solution to #981201 that Marcin Owsiany proposed in
https://salsa.debian.org/xorg-team/xserver/xorg-server/-/merge_requests/6
was to make -noreset the default, but the Xorg team are concerned that
changing the default could break expectations.

(I wonder whether this might mean that xvfb-run should have a
debhelper-like concept of having a compat level, defaulting to -reset in
compat level 1 and -noreset in compat level >= 2? But perhaps that's
overkill.)

The workaround that many packages are now using for their build-time
tests and/or autopkgtests is to use `xvfb-run -a -s "-noreset"` as their
"adverb" command.

    smcv