[mythtv] Ticket 9177 / HD-PVR channel change

Daniel Kristjansson danielk at cuymedia.net
Fri Dec 31 22:23:29 UTC 2010

On Fri, 2010-12-31 at 17:13 -0500, Brian C. Huffman wrote:
> All,
> Has there been any thought as to what is causing the problem in ticket 
> 9177 ( "Error opening jump program file buffer" when changing channels 
> in live TV" )?  The poster has an HD Homerun, but I'm seeing the same 
> type of problem with an HD-PVR.  This problem exhibited itself fairly 
> recently - I think it's even post-v24.  It has shown up in the .24-fixes 
> branch which is extremely unfortunate as I was hoping to stabilize for a 
> while and figured fixes ought to be safe.

It looks like this is a deadlock of sorts caused by a change in the
video player threading model for 0.24. It isn't a true deadlock because
MythTV can break out of it. It is also non-deterministic, it looks like
this will only occur if the frontend attempts to read a file before the
backend has written the first 2048 bytes of the file to disk. As a
result some people will see this quite a lot and others will never
see it, depending on the particulars of their setup.

I believe Mark Kendall and I are on the same page as to how to fix it,
change the RingBuffer::safe_read() API so that we pass errors (temporary
and permanent) to higher levels and handle them there. It's a matter
of finding the time to work in it.

-- Daniel

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