<html> <head> <style></style> </head> <body class='hmmessage'> Thanks so much Chris for confirming. With that knowledge I managed to reproduce and eliminate the bug. There was a thread trying to read this surface stuff when it *really* shouldn't :) I'm having great fun with cairo doing animations and stuff. Hopefully I'll be able to post a video of my app at some point :) Best Regards Julien > Date: Sat, 5 Dec 2009 08:50:18 +0000 > To: julien_bramary@msn.com; cairo@cairographics.org > Subject: Re: [cairo] Can an expert look at this stack trace? > From: chris@chris-wilson.co.uk > > On Sat, 5 Dec 2009 06:06:51 +0100, Julien Bramary <julien_bramary@msn.com> wrote: > > > > Hello all, this is my first post to this list. > > Welcome, we hope you are having fun using Cairo, and this does not mar the > experience! > > > I am writing a threaded cairo application and I need help understanding a rare-ish bug. > > I'm still using cairo 1.8.8 but considering an upgrade to get the nice profiling tools. > > > > Every so often I get the following crash: > > cairo-board: cairo-surface.c:406: cairo_surface_reference: Assertion `((*&(&surface->ref_count)->ref_count) > 0)' failed. > > /usr/lib/libcairo.so.2(cairo_pattern_create_for_surface+0x7d) [0x7f2e24966a6d] > > /usr/lib/libcairo.so.2(cairo_set_source_surface+0x46) [0x7f2e249525b6] > > ./cairo-board [0x40f591] > > > > If understand correctly my application is calling set_source_surface on an invalid surface? > > Does it mean the surface was destroyed? This is very possible as the code is quite convoluted. > > Yes, this means that cairo_surface_reference() has been called on a > surface that has already been freed. In this particular case you are > trying to use a source surface that has already been destroyed. > > > The rarity of the crash (less than 1/100) makes me think it might be a timing issue with a thread destroying the surface while another one tries to read it with cairo_set_source_surface but I can't see where as everything should be locked... > > I'd like to know if an expert can confirm. > > Ah the spectre of threads. If you even suspect you have a race here, you > do. The thread using the surface as a source must own a reference to the > surface, so there should be no doubt as to the validity of that surface > and hence no race. So either you've violated that principle or you have > a double-free somewhere in your code. > -ickle > > -- > Chris Wilson, Intel Open Source Technology Centre <hr />Windows Live: Make it easier for your friends to see <a href='http://www.microsoft.com/middleeast/windows/windowslive/see-it-in-action/social-network-basics.aspx?ocid=PID23461::T:WLMTAGL:ON:WL:en-xm:SI_SB_2:092009' target='_new'>what you’re up to on Facebook.</a></body> </html>