[OpenIndiana-discuss] Comments, please! problem with ffmpeg that seems to be a problem with OI at driver or basic library level

[Bob Friesenhahn]

On Wed, 15 May 2013, Hans J. Albertsson wrote:

> I regularly download ( quite legally, I'm told ) HLS streams from svtplay.se 
> using ffmpeg and a stream URL obtained by scraping the svtplay.se/<show-link> 
> page.
>
> This works very well in Ubuntu and Windows on a separate PC.
>
> Under OI and even in W XP inside a VirtualBox VM it hangs, seemingly at 
> random positions in the stream. The ffmpeg process is totally inert upon 
> hanging, and one must kill it by two consecutive ^C. It doesn't respond to 
> the on the fly command language at all.
>
> The hang is in pollsys, as demonstrated by the following truss -f output 
> excerpt from the hanging ffmpeg process.
>
> 29961:    pollsys(0x08046768, 1, 0x08046718, 0x00000000)    = 0
> 29961:    pollsys(0x08046768, 1, 0x08046718, 0x00000000)    = 0
> 29961:    pollsys(0x08046768, 1, 0x08046718, 0x00000000)    = 0
> 29961:    pollsys(0x08046768, 1, 0x08046718, 0x00000000)    = 0
> 29961:    pollsys(0x08046768, 1, 0x08046718, 0x00000000)    = 0
> 29961:    pollsys(0x08046768, 1, 0x08046718, 0x00000000)    = 0
> 29961:    pollsys(0x08046768, 1, 0x08046718, 0x00000000)    = 0
> 29961:    pollsys(0x08046768, 1, 0x08046718, 0x00000000)    = 0
>
>
> I guess that the fact it happens in the W XP in vbox the same as in OI itself 
> indicates the problem somehow involves code residing under the Vbox VM, even, 
> and that it's some sort of incompatibility that only will actually have an 
> effect under some sort of race or race-like condition.
>
> I'd appreciate any insight any of you could offer into what this entails

I see similar issues with the VLC player which decides that 'mplayer' 
is too slow and not able to keep up.  Without taking time to diagnose, 
my first guess would be a buffering issue which causes the hang.  The 
software is developed under Linux and may have certain buffering (e.g. 
pipe buffering) expectations.  Confusion between the buffering and any 
locking (or even just the buffering) might cause a deadlock in the 
software.

To diagnose, try using 'pstack' on the processes which are hanging and 
see where they are hung.

Bob
-- 
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/