Re: [fluid-dev] Questions about Gleam

[Miguel Lobo]

Events can be generated and consumed at quite a high rate, so event memory management can be critical for performance and especially latency.  Applications might implement different solutions to deal with this, so I wanted to keep GleamCore flexible in this area.  In fact, the non-optional parts of GleamCore don't do any allocation or de-allocation of events; the MIDI converter does, but it's just meant to be a helper to deal with MIDI data and its use by the application is completely optional.  Perhaps it should be moved out of GleamCore, as nothing in GleamCore depends on it.

Another general target is to avoid any calls to memory allocation functions (which have potentially unbounded duration) in the synthesis thread.  At the moment we're still quite far from that target, but the freeing of events is the most important place, I think, where this idea impacts design rather than just implementation, so I wanted to try to get it right as early as possible.

Virtual functions have a cost both in compile-time optimization and run-time performance and should be avoided in time-critical code whenever reasonable.  Events could have a virtual callback to notify of their consumption, but that would be quite expensive.  The intended way to know when a point has been reached in the event queue is the condition sync event, which has minimal cost for the synthesis thread.  An example of its usage its provided in playmidi.cpp:

    /* add a condition sync event so we know when all events have been played */
    GleamConditionSyncEvent& endEvent(events.addType<GleamConditionSyncEvent>()());
    endEvent.freeList = &freedEvents;
    endEvent.time = lastTime;

[...]

    /* wait until the end event is played */
    endEvent.conditionSync.wait();

Hope these answers some of your questions.

Regards,
Miguel

On Sun, Apr 20, 2008 at 4:13 PM, Guillaume Pothier <address@hidden> wrote:

Hi Miguel, thanks for your help.
Indeed I think the autorepeat feature should be implemented outside of
GleamCore. Maybe I wasn't very clear in my previous mail, but what I
wanted to do was to provide a subclassed list to the midi loader so
that I could be notified when events are consumed. So all this extra
code was outside of Gleam, the only change I had to do to Gleam itself
was to declare the addNode methods of GleamList virtual.
I'm wondering, what is the intended use of this freed events list? I
guess it is for deallocating the memory of the events, right? I was
thinking that it might be more generic to use a callback, rather than
storing the events in a list. So if someone needs to have a list of
freed events, they can do it by providing a proper callback. If
someone wants to do something else, like this autorepeat stuff, or
directly deleting the events, they can also do it. What do you think?
g

On Mon, Apr 21, 2008 at 3:20 AM, Miguel Lobo <address@hidden> wrote:
> Sorry again, I did not try compiling with the debug log disabled.  It should
> work now.
>
> It's important to keep the intended purpose of GleamCore as simple and easy
> to understand as possible (and reasonable), so I think a feature like your
> propose would be better implemented outside GleamCore.  For example, in the
> playmidi example, you have this code:
>
>     /* add a condition sync event so we know when all events have been
> played */
>     GleamConditionSyncEvent&
> endEvent(events.addType<GleamConditionSyncEvent>()());
>     endEvent.freeList = &events;
>      endEvent.time = lastTime;
>
> [...]
>
>     /* wait until the end event is played */
>     endEvent.conditionSync.wait();
>
> At that point you could add all events again instead of exiting.
>
> Hope this answers your question.
>
> --
> Miguel
> Check out Gleam, an LGPL sound synthesizer library, at
> http://gleamsynth.sf.net
>
>
>
>
> On Sat, Apr 19, 2008 at 11:23 PM, Guillaume Pothier <address@hidden>
> wrote:
> > Hi Miguel, thanks for your reply!
> > I updated my working copy and now I have other errors (string.h is not
> > imported in debuglog.h, and bad call at sf2voice.cpp:551; for now I
> > just commented the offending statement out)
> >
> > I started playing around with Gleam and I was wondering how could I
> > implement a "repeat" feature: I would like to load a short midi file,
> > and have it playing over and over again. I thought that the simplest
> > mean of doing that would be to overload the freeList so that whenever
> > an event is added to it, I push it back to the synth, with an updated
> > timestamp. First of all, does it sound like a reasonable solution?
> > Second, to to that I would need the addNode method of GleamList to be
> > virtual. Could that be?
> >
> > Regards,
> > g
> >
> >
> >
> >
> > On Sun, Apr 20, 2008 at 2:51 PM, Miguel Lobo <address@hidden> wrote:
> > > Hi,
> > >
> > > Gleam is still very related to fluidsynth so I hope people won't get
> > > offended if there are questions about it here.  However, I don't always
> read
> > > all posts in this list (especially when I'm very busy at work like in
> the
> > > last few weeks), so please CC me on any message about Gleam to be sure
> it
> > > doesn't get lost.
> > >
> > > The reason Gleam from SVN wasn't compiling was that I had a change half
> > > checked-in.  I've now completed the check-in, so it should build.  This
> > > change, which is what I've been working on recently, basically adds an
> > > interface to generate useful debug information.  I'm trying to use it to
> > > track down severe clicking problems that seem to appear in some
> particular
> > > songs.
> > >
> > > In response to your other questions:
> > >
> > > - Gleam might well be more CPU-intensive than fluidsynth at this point;
> I
> > > haven't checked.  The reason is I'm focusing on getting functionality
> right
> > > before looking into performance optimisations.  Anyone who wants to look
> > > into the latter is welcome right now, of course.
> > >
> > > - Gleam has been designed with the idea of being able to combine
> multiple
> > > synthesis models (or "subsynths" as I've called them) in a single
> logical
> > > synthesizer.  Currently only the only implemented subsynth is based on
> the
> > > SF2 spec, but I hope other subsynths will be added in the future.
> > >
> > > As always, anyone who wants to do *any* type of development on Gleam
> will
> > > have my full support as far as answering questions and so on.
> > >
> > > --
> > > Miguel
> > > Check out Gleam, an LGPL sound synthesizer library, at
> http://gleam.sf.net
> > >
> > >
> > >
> > > On Sat, Apr 19, 2008 at 5:28 PM, Guillaume Pothier <address@hidden>
> > > wrote:
> > > >
> > > >
> > > >
> > > > Hi,
> > > > I hope this place is more or less appropriate to ask questions about
> > > Gleam.
> > > > So here are a few questions:
> > > >
> > > > - Gleam from svn is not building right now, I get those errors:
> > > > /home/gpothier/tmp/gleamsynth/GleamCore/src/sf2/sf2voice.cpp: In
> > > > constructor 'GleamSF2Voice::Private::Private(GleamCore&,
> > > > GleamSF2SubSynth&, GleamSynthConfigurationV1&, GleamSF2Voice&)':
> > > > /home/gpothier/tmp/gleamsynth/GleamCore/src/sf2/sf2voice.cpp:169:
> > > > error: 'class GleamArray<GleamSF2Generator>' has no member named
> > > > 'setCountWithoutCopy'
> > > > /home/gpothier/tmp/gleamsynth/GleamCore/src/sf2/sf2voice.cpp: In
> > > > member function 'bool GleamSF2Voice::on(const GleamNoteEvent&,
> > > > GleamSF2Zone&)':
> > > > /home/gpothier/tmp/gleamsynth/GleamCore/src/sf2/sf2voice.cpp:235:
> > > > error: 'class GleamArray<GleamSF2Modulator>' has no member named
> > > > 'count'
> > > > /home/gpothier/tmp/gleamsynth/GleamCore/src/sf2/sf2voice.cpp:236:
> > > > error: 'class GleamArray<GleamSF2Modulator>' has no member named
> > > > 'count'
> > > > /home/gpothier/tmp/gleamsynth/GleamCore/src/sf2/sf2voice.cpp: In
> > > > member function 'void GleamSF2Voice::updateModulators(bool)':
> > > > /home/gpothier/tmp/gleamsynth/GleamCore/src/sf2/sf2voice.cpp:722:
> > > > error: 'class GleamArray<GleamSF2Modulator>' has no member named
> > > > 'count'
> > > >
> > > > Is it okay to replace all those "count" by "capacity"?
> > > >
> > > > - Is Gleam more CPU-intensive than fluidsynth?
> > > > - I'd like to eventually have a fixed-point synthesizer. If I have
> > > > time I might have a try at writing one. Where would it fit in the
> > > > design of Gleam?
> > > >
> > > > Regards,
> > > > g
> > > >
> > > >
> > > > _______________________________________________
> > > > fluid-dev mailing list
> > > > address@hidden
> > > > http://lists.nongnu.org/mailman/listinfo/fluid-dev
> > > >
> > >
> > >
> >
>
>

-- 
Miguel
Check out Gleam, an LGPL sound synthesizer library, at http://gleamsynth.sf.net