[FFmpeg-devel] [PATCH 3/3] Add assert that the avcodec lock isheld when initializing static VLC tables.

[Reimar Döffinger]

On 3 Dec 2012, at 01:09, "Don Moir" <donmoir at comcast.net> wrote:
>> On Sun, Dec 02, 2012 at 05:35:33PM -0500, Don Moir wrote:
>>> Looks to me there are hundreds of places av_assert0 is called and
>>> not just a few and av_assert0 calls abort. The thing is I would like
>>> to have an easy indication where and why it failed. This is simple
>>> enough for you isn't it ?
>> 
>> As Nicolas pointed out, the why is completely unknown (otherwise we
>> probably should indeed not be using an assert).
>> We do not have a context around either most of the time I'm afraid.
>> 
>>> If appropriate it could be ff_abort (AVFormatContext,reason); or
>>> whatever. ff_abort is set by app. With your aborts you have the
>>> opportunity to give it back to the app in a cleaner way if you
>>> choose.
>> 
>> While that shouldn't be a big issue, what would you then do
>> after your callback is being called?
>> Without context and reason being available you won't really have
>> anything more than you'd get in a signal handler...
>> 
>>> We actually already have a handler in place but its not convienent
>>> for tracking the actual cause of the problem somewhere in ffmpeg and
>>> by allowing a settable abort call this would help to isolate the
>>> problem.
>> 
>> If by "handler" you mean signal handler, I'd think the obvious question
>> would be: why not improve that signal handler so it can provide you
>> all the information you need?
>> Obviously not as easy as it sounds, but at least a backtrace should
>> be possible and is definitely a very good start.
> 
> Yep could do this but essentially the trace is going to be some high level ffmpeg call (we already know that) with probably quite a bit of depth of assembler.

You should be getting file and line number as long as you have the debug info around (if you have it make a core dump, it's even enough to have it on a different machine).
The build system might not support this that well yet.
There is also the option of having a new log level for av_log so you can have it print only these absolutely critical things (and yes a abort callback is an option as well), but it would not solve the problem for other crashes, and it will only give you the lowest function which will still be useless in a lot of cases.