[iiwusynth-devel] Re: unloading a soundfont

[Peter Hanappe]

Markus wrote:

> some thoughts about unloading sound fonts, This has been on my mind now
> for a while.
>
> - The unload routine has to wait, until the DSP loop in the DSP thread
> has run through one buffer. Otherwise there is no way to stop a voice,
> which uses the soundfont in question and is just in the middle of a
> buffer.
> - The unload routine could terminate all voices using the soundfont, and
> block until the DSP thread has finished the current block. Don't like
> that. Not at all.

I agree. We can do better.


> The best I came up with so far:
> - The unload routine flags the sound font as unloaded, so that no new
> voice processes may use it.
> Then we keep the old soundfont in memory and only unload it when the
> next sound font is loaded (triggered by the 'load' function), assuming
> that all voices have finished in the meantime.

Also, remove all presets of that soundfont from the MIDI channels.

We could add a 'reference count' into a soundfont: every time a voice
uses a preset from a soundfont, the reference count of that soundfont
is incremented. When the voice is finished, we decrement the refcount
again. When an unload request comes and the soundfont has a refcount
equal to zero, we unload it immediately otherwise we try to do it later.
When? At the next load request? That might not be good enough, because
the risk exists that soundfont stays in memory for a long time. At every
'noteon' and 'noteoff' event? That may not be good, too. That means that
real-time threads can no longer call this function!

Antoine wrote:
> Why not using the timer functions (in iiwu_sys.h) to schedule a
> callback
> sometime after the current buffer is done, that will do the cleanup ?
> This way, there is no need for the iiwu_idle function.

Yes, we could spin off a timer thread to do the work. It checks every N
msec (~1000 msec) if the soundfont is no longer used (refcount=0) and
frees it if possible.
This doesn't work on macos 9, though (can't free memory in interupt).


Cheers
Peter