[vlc-devel] [PATCH] dvdnav: add Demux submodule

[Rémi Denis-Courmont]

Le 2015-03-18 01:46, Luca Barbato a écrit :
>> I mean it locks up if the stream read does not return (in any 
>> reasonable time
>> frame), in other words if you have a (long) blocking read. That 
>> situation is
>> not possible for a regular file. Regular file I/O is never blocking: 
>> it either
>> completes or fails straight away.
>>
> And access doesn't have tunable timeouts with poll so the problem
> gets quite substantial.

I fail to see how a time-out would help here. There are two things that 
you absolutely want to avoid:
1) getting stuck permanently even if the user tries to stop, and
2) reading large chunks of data at once, that might block the input 
thread for too long, leading to buffering and UI problems.

The first problem requires a solution at the access level. This is 
already solved for native VLC plugins using net_Read(). But this was 
knowingly and conveniently ignored by the multiple authors of remote 
file system using third party libraries, as well as RTSP/live555 and 
AVIO. Agreeably, this problem is in no way specific to optical disc 
formats.

The second problem requires a solution at the demux level. The proper 
solution is to set pf_demux to NULL and perform all I/O in a separate 
thread. The "compromise" solution consists of reading only "small" 
chunks of data and returning from pf_demux in-between. DVD and BD 
parsers fail miserably here because that was never a problem with 
regular files and local drives.

-- 
Rémi Denis-Courmont