[Xcb] Assert in xcb_io.c:542

Jamey Sharp jamey at minilop.net
Wed Nov 4 22:56:37 PST 2009

On Wed, Nov 4, 2009 at 6:55 PM, Graeme Gill <graeme at argyllcms.com> wrote:
> Apparently what happens is the user hotplugs a new display but doesn't
> configure it:
> 1. Start with only laptop panel connected.  dispwin works.
> 2. Plug in VGA cable.  dispwin fails.
> 3. xrandr --output VGA1 --right-of LVDS1 --auto.  dispwin works again.
> (I'm not clear on what is exactly meant by "dispwin fails", although I
> suspect it means the xcb assert gets triggered.)

The single most important piece of information we could get is a stack
trace. We'd need to know what called _XRead when the assertion fired.

> OK, thanks to your hint I got it working to the localhost and got a capture
> of normally working situation. Is it worth asking the user who reported
> the problem to do the same ?

If for some reason it's easier to get a network trace than a stack
trace, then sure, it would help. But a stack trace is probably all
that's really necessary for this bug.

> A better error handler is welcome, but I'm not sure If I'm going
> to re-write using xcb just yet though, sorry :-)

Just to be clear: You don't have to re-write all your code using XCB.
You can replace just one Xlib call with a call into XCB, if you want.
But I didn't really expect you to go for it. :-)


More information about the Xcb mailing list