Re: External PCM plugin SDK

[Takashi Iwai <tiwai@suse.de>]

At Thu, 10 Feb 2005 19:21:18 +0100,
I wrote:
> 
> At Thu, 10 Feb 2005 19:06:01 +0100,
> Marcel Holtmann wrote:
> > 
> > Hi Takashi,
> > 
> > > > > > > > Problem now is that XMMS closes the device and re-opens it when changing
> > > > > > > > the track and even when switching to its next track. This is problematic
> > > > > > > > when using Bluetooth, because I need to keep the underlaying connection
> > > > > > > > alive. Any idea?
> > > > > > > 
> > > > > > > Yeah, that's bad behavior of xmms.
> > > > > > > I'll try a hack later...
> > > > > > 
> > > > > > Another way is that I implement somekind of keep alive mechanism inside
> > > > > > the plugin, but what I have seen so far is that it is directly unloaded
> > > > > > when it is no longer used. So the 1:1 mapping of open/close is not a
> > > > > > good thing and maybe there should be some keep alive and reset inside
> > > > > > the ALSA library to help here out.
> > > > > 
> > > > > The delayed close in the plugin is of course good to have.
> > > > > My only concern is that the code would be complicated to handle
> > > > > races.
> > > > 
> > > > actually I see a lifetime race inside the plugin if I try to handle it
> > > > by myself. When the close() callback is called, I must free all of my
> > > > allocated resources, because the shared object will be unloaded, right?
> > > 
> > > Yes, the close callback should clean up everything since there is no
> > > distinction between close and unload, so far.
> > 
> > if the ALSA core is not handling the XMMS behaviour for us, I really
> > need something to distinguish between close and unload.
> > 
> > What do you think about doing it like with kernel modules? Means we add
> > an init and an exit entry point inside the plugin. The rest is done via
> > callbacks. With this we should be able to register a PCM and also the
> > mixer controls for it within the same plugin.
> 
> That's a good idea.

... and doesn't work as it is, unfortunately :-<

dlcose() is called after snd_pcm_close().
We may need to build object caches in alsa-lib.
This will improve the perfomance eventually, too.


Takashi


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