[Bf-committers] Save session recovery on SIGSEGV

[Ton Roosendaal]

Hi,

>> Cool, I wouldn't have thought the state is sane enough still to save  
>> a file
>> in that situation.
>
> It should be, assuming that the error didn't arise while making an  
> undo push.
>
> It depends on how the undo session saves works; if it simply calls a  
> normal save, then yes there could be problems, but if it saves an undo  
> push, then there shouldn't be a problem.
>
> Ton, am I right?


Yes, the undo system fills simple data buffers with differences. When  
that's done OK a BKE_undo_save_quit() is safe to call since it only  
goes over a list and dumps data binary to disk.

In the good old NeoGeo days we had something similar for a while, but  
decided to drop the feature because it did more harm than pleasure back  
then. The main reason for 'harm' was it then called a regular  
file-save, which regularly resulted in corrupted files. By using the  
undo system you won't save a corrupt file easily, but is still possible  
though (undo 'pushes' can be created on corrupted data before it  
detects the corruption). Another reason was it didn't write nice crash  
reports (core dumps) anymore.

For such a feature to make it in official releases, we have to look at  
the following;

- find out if something similar can be done for Windows; you use a  
typical unix feature here (OSX will work btw). Having a unix-only  
feature in Blender isn't forbidden, but not preferred. :)

- make sure the signal() for 'crash.blend' saving is switched off  
during crucial stages like;
   - file saving and reading
   - undo pushing/popping
   - while saving crash.blend itself!

- find a good way to activate the option, not only as user-preset but  
also for developers. Best would be if this signal() trap doesn't bypass  
system level debugging (e.g. write core dumps or crash reports. I use  
(or enforce!) crashes all the time for debugging.

-Ton-


------------------------------------------------------------------------ 
--
Ton Roosendaal  Blender Foundation ton at blender.org  
http://www.blender.org