[mythtv-users] Help needed for scripted recordings

[Klaas de Waal]

On Mon, 30 Mar 2020 at 21:56, Bill Meek <keemllib at gmail.com> wrote:

> On 3/30/20 2:15 PM, Klaas de Waal wrote:
> > As I understand it mythfrontend communicates with mythbackend with the
> > so-called mythprotocol, while the ServicesAPI is implemented as a HTTP
> > webserver on the same mythbackend. This suggests that the frontend, via
> the
> > mythprotocol, does something different than the ServicesAPI.
> > This definitely needs some thinking, it might even be necessary to
> > understand what the code is actually doing.... which is usually not need
> to
> > fix crashes. Just find the null pointer....
>
> The DeleteRecording endpoint:
> https://code.mythtv.org/cgit/mythtv/tree/mythtv/programs/mythbackend/services/dvr.cpp#n315
>
> may end up here:
> https://code.mythtv.org/cgit/mythtv/tree/mythtv/programs/mythbackend/mainserver.cpp#n1321
>
> But there's another place in mainserver that handles the DELETE_RECORDING
> message. The other one's:
>
> https://code.mythtv.org/cgit/mythtv/tree/mythtv/programs/mythbackend/mainserver.cpp#n635
>
> Looks like mythprotocol to me.
>
> Thanks for the pointers!
>From both places really soon the common code is called. I do not think the
code itself is at fault.
I have not yet checked it but I guess that the MythProtocol and the
MythSocket processing is done in different threads and that this does
infuence the timing.
If I  add a 100ms delay at a critical place, or exit out of the loop once
the recording is found (the patch in the ticket), then that does fix the
crashing problem. Which is a strong indication of a locking/threading
problem so that is the next spot to look.
I guess that if I hack the MythSocket so that the delete event sent back
and processed via the MythProtocol (and on the thread of the MythProtocol)
then it will crash.


> Good news that it happens from the combined FE.
>
> When I tried the test, the 1st use of Dvr/DeleteRecording always worked and
> the next <n> always failed because the recording was successfully deleted.
>
> Yes this is how it works. I use a "vcr.py" command that makes only one
recording which is then deleted This command is inside a bash "while [ 1 ]
; do_command; done" loop to run forever. And this three times for three
channels, of one multiplex received by one tuner. This then runs forever.
If I delete recordings-in-progress with the GUI then within a few tries the
backend crashes.....

Thanks,
Klaas.
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