Bug#848063: +patch: ri-li FTBFS on single-CPU buildds

[Steve Cotton]

On Sun, Feb 19, 2017 at 09:38:12PM +0100, Steve Cotton wrote:
> Sorry, but it's turned out that my patch either doesn't completely
> avoid the bug, or doesn't avoid another bug which gives the same error
> message.  The build has failed on arm64.

I've tried to reproduce this locally (on amd64, not arm64).  With my
patch, I can't replicate the failure. Santiago, please would you test
how it fares on your autobuilders?

Testing by removing my patch and trying to debug the root cause, I
haven't found the cause yet.  But I think it will need a complex patch
to either libsdl1.2 or xvfb, and I don't think this bug justifies any
complex patch during the freeze.

It seems that one of the XOpenDisplay calls in SDL's X11VideoInit fails.
Having a GCC breakpoint at the start of X11VideoInit, or running MakeDat
under strace, makes the bug unreproducible.  Adding a long sleep to the
last point in the ri-li package's code before SDL_Init doesn't help.
Running another SDL programe first in the same xvfb server doesn't
change anything, so it seems that the server can't be primed in advance.

Markus, I'm really sorry that what looked like a risk-free patch has
caused a failed rebuild.  Depending on the TC's ruling, does it sound
sensible to say that 2.0.1+ds-4 is in Stretch, and -5 doesn't affect -4?

Steve