This was found today when running Thunderbird tests. Example test failure: <https://tbpl.mozilla.org/php/getParsedLog.php?id=31889766&tree=Thunderbird-Trunk>. I believe this to have been caused by bug 897452

Benoit, you'll fix or assign this to somebody else to fix?

Depends on how quick this must be fixed. I'm already busy with another, more certain, more frequent regression from PTexture: bug 949347.

To give some background: This assertion is hit with OMTC when we try to create a TextureHost (the texture abstraction on the compositor process/thread) before a compositor was created. In this case it looks like we failed to create a compositor in nsBaseWidget, but are trying to create texture client/host pairs anyways. I don't think Thunderbird is supposed to use OMTC, espectally since it disables hardware accelerated layers and OMTC ot the moment doesn't work too wall without it IIUC. So we should just make sure that thunderbird has the pref "layers.offmainthreadcompositiong.enabled" = false.

Expanding Dan's horizons, lets see if he can do this :)

Nical, given how little resources Thunderbird has, it's probably vital for them to use the same gfx configuration as Firefox. If they're the only ones to use non-OMTC on Mac, they're run into random bugs that no-one cares about...

(In reply to Nicolas Silva [:nical] from comment #3) > espectally since it > disables hardware accelerated layers Dang. Does it? That's crazy - for the reason said in comment 5. Why don't we use GL layers in Thunderbird? As GL layers have been what most Firefox/Mac users have been using for the past 2.5 years, it is the conservative option there, much more conservative than using basic layers that fewer and fewer firefox users use on Mac.

I'm testing a patch on try that uses the disabled OMTC to see if that fixes the immediate issue. Digging into history, hardware acceleration was disabled in bug 689742 to improve battery usage. Given comment #5, this may need to be revisited, but I will keep that discussion out of this bug.

bug 689742 comment 0 says the reason is that back then, GL layers triggered the discrete GPU on dual-GPU macs. That's long not been the case anymore. You can safely turn on GL layers, that won't trigger the discrete GPU. What does trigger the discrete GPU is WebGL, and only during the lifetime of any WebGL context.

Milan, speaking with Benoit, we should have the Thunderbird team remove the preference that disables OMTC and then we should handle any bugs that fall out from that. Who should I assign this to?

Irving, what's the best way for us to get this change in?

Graphics acceleration was turned back on in bug 950133, and the layers.offmainthreadcomposition preferences appear to have the same default settings as in Firefox. Is the problem still occurring?