[Bf-committers] Using assert()?

Torsten Rupp torsten.rupp at gmx.net
Fri Aug 13 10:23:18 CEST 2010

Dear Sergey,

> IMHO assert will help only with obvious problems (as you wrote NULL
> pointers, i.e.) Such problems would be easily catched by gdb or
> valgrind. So i don't think asserts are necessary for pointers
> check.

The problem with gdb or valgrind and any other tool is that you must 
execute Blender with it. If you just use Blender as a user and it is 
crashing for some reason and the situation is hard to reproduce I 
know nothing about the problem. Currently I have such a problem: it 
is crashing in around 50% of all runs, but for some reason never 
inside gdb :-(. Depending on the bug a crash even may occur hours 
after starting it, e. g. when rendering a complete animation. A core 
dump may be the only usefull source for information in that case 
(currently I try this), but unfortunatelly bugs which cause a SigSegV 
and a core dump may be located at completely different locations in 
the sources than the location where the SigSegV occur. To get aware 
of all correlations and to understand what went wrong is quit a 
difficult job if you only have broken fragments in your hands :-)

Thus I think some basic self-checking inside the application would 
help to get some early hint where to look for problems even before the 
application terminates with a SigSegV or do some other strange thing.

> Another thing is memory damage (i.e., due to invalid write range to
> dynamically allocated memory) In this case SigSegV can't be caught
> reliable. But such mistakes can't be handled with asserts. valgrind
> should help with handling such problems.

valgrind is a very good tool, but it is hard to use with big 
applications because it slow down the execution speed dramatically. I 
just tried it with the problem I'm currently investigating: it took 
around 5min to see the SigSegV without using valgrind when I just call 
Blender directly. But with valgrind it took around 50min to get to the 
point where the error may become visible - but I did not get the 
error in this run nor do I see anything which seems to be 
related to the problem :-(

BTW: there are many issues reported by valgrind which must be 
filterted out. Of course I'm not sure if this output of valgrind are 
real issues or just false-positives. This have to be investigated in 
detail to clarify it.

Nevertheless, if nobody thinks asserts() may help to track down bugs, 
I will accept this. I just wanted to know if there is any general 
directive how to handle such problems.


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