Hm... still, I can't get that value from within a patch because of your design
constraints, right?
On Tuesday, October 6, 2015 2:20 PM, Miller Puckette <[email protected]> wrote:
So in that case you'd really want a different metric, perhaps 'what was the
minimum fill count while the file was playing'.
cheers
M
On Tue, Oct 06, 2015 at 05:40:27PM +0000, Jonathan Wilkes via Pd-list wrote:
> But as Matt's student I want to be able to measure the time it takes to open
> the file, to make a more informed decision when I design my patch. I wantthe
> pure data when I'm only opening a few soundfiles, and then Iwant the pure
> data when I try to open lots of files. Pd already gives me[realtime] which I
> could use to create non-deterministic patches. Obviouslyits author realized
> that the ability to measure time outweighs the risk of doingthat. One would
> assume that same tradeoff to be equally important, if notmoreso, for the few
> instances of object behavior which [realtime] cannotmeasure.
> The other students are now rolling their eyes. I think they're on to me.
> -Jonathan
>
>
>
> On Tuesday, October 6, 2015 12:11 PM, Miller Puckette <[email protected]>
>wrote:
>
>
> A worthy question.
>
> If you want the soundfile to start exactly when you specify it (I think this
> should normally be the case :) then it's beside the point exactly when the
> computer could have coughed it up - it only matters that it be there by the
> desired time.
>
> If you want the soundfile to play "whenever the computer can manage it" - and
> the sooner the better - well, then a "ready" message would be useful. I
> imagine one could shave off 1/5 second or so, but it would be inconsistent.
> Perhaps this is useful in some cases but I don't think it would be often -
> and the downside is that it wouldn't be deterministic (a fundamental design
> principle of Pd).
>
> cheers
> Miller
>
>
> On Tue, Oct 06, 2015 at 03:58:38PM +0000, Jonathan Wilkes wrote:
> > If I were one of Matt's students, I'd ask why this "Pure Data readsf~
> > business" won't just tell me when it has actually opened the file. Why
> > does thecomputer get to know when it's ready, but we students have to guess
> > bylistening for glitches?
> > -Jonathan
> >
> >
> >
> > On Tuesday, October 6, 2015 1:02 AM, Matt Barber <[email protected]>
> >wrote:
> >
> >
> >
> > 4) Has anyone ever “broken” these objects or experienced glitching?
> >
> > Once in 2005 we were having awful trouble streaming through Pd but we were
> > never sure whether it was [readsf~] per se, a very slow disk, or xruns in
> > ALSA/JACK, and we had only one performance laptop available. My best guess
> > is that it was an ALSA/JACK problem, since other software had a few issues
> > with glitching just on realtime audio processing.
> > pthread_mutex_lock() ... This might be a good time for a PSA for interested
> > newcomers to Pd, though, if any happen to be following this thread (ahem).
> > Having taught Pd for some 10 years now, one bad habit I've seen nearly
> > every student fall into is failing to preload the file before playing,
> > trying to do the initial read and the playing at the same logical time.
> > Usually there isn't a problem, but once in a while a taxed system that is
> > already streaming several files can glitch hard on a new stream. I've
> > attached a generic [readsf~] idiom that has been useful for first-year
> > students when they want to jump in and get Pd to play some sound files with
> > a GUI after they've fooled around with the control examples and
> > oscillators. This is before we get into event triggering, so the clunky
> > multiple play/stop buttons is edited out later on; the main thing is how to
> > keep the file open at all times. This turns out to be even more important
> > for rehearsal than for performance, when you need to be able to jump around
> > at will. ... pthread_mutex_unlock()
> >
> >
> > On Tue, Oct 6, 2015 at 12:15 AM, Miller Puckette <[email protected]> wrote:
> >
> > I think you can get away with sharing a lock between two high-prioroty
> > processes as long as neither one holds the lock for more than a small
> > amount of time and if the OS can be counted on to give control to a
> > real-time
> > process quickly once it becomes runnable (i.e., if it's blocked on a lock,
> > once that lock is released).
> >
> > The situation I don't know about is this: if Pd's main thread failed to get
> > the lock, so that control (presumably) passed back to the other thread that
> > had the lock, how much time can pass before the other thread blocks on
> > something so that control (again presumably) gets passed back to the main
> > thread?
> >
> > But anyway, since neither thread holds onto the lock for more than a few
> > lines of C code (with no system calls) it's probably blue-moon rare that the
> > scheduler interrupts one thread right in the middle of a critical section
> > and
> > passes control to the other one that then blocks. So this is essentially
> > untested.
> >
> > Threads can never be used confidently in a real-time situation. But I don't
> > see any reasonable way without them to implement readsf~/writesf~, so there
> > we are...
> >
> > cheers
> > Miller
> >
> > P.S. one can issue non-blocking reads/writes, but there's also "open" which
> > is much more likely to hiccup than "read", and I don't know of any async
> > open
> > call in any OS.
> >
> >
> > On Tue, Oct 06, 2015 at 03:10:31AM +0000, Jonathan Wilkes via Pd-list wrote:
> > > 1) One thing I noticed is that the article you cited seems to focus
> > > on tasks not critical to the computation/delivery of audio samples.For
> > > example, if your program were blocking or locking in order to do a
> > > GUIupdate. But here, the data must arrive in time to compute the next
> > > block. If ittakes too long to read the next portion of the sound file,
> > > then you're going to geta glitch.
> > > But I'm not sure I really grasp how locking works, nor really the whole
> > > file i/oprocess in general.
> > >
> > > Here's a naive question: why can't you just tell the OS to treat the file
> > > asif it were a non-blocking socket, add the fd to Pd's event loop with
> > > sys_addpollfn, and then receive the incoming data to the relevant
> > > function?(Warning: some or all of the above may technically be
> > > gibberish...)
> > >
> > > -Jonathan
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > On Monday, October 5, 2015 10:01 PM, Robert Esler
> > ><[email protected]> wrote:
> > >
> > >
> > > I’m trying to understand why readsf~ and writesf~ work so well.
> > >
> > > I’m particularly referencing Ross Bencina’s article:
> > > http://www.rossbencina.com/code/real-time-audio-programming-101-time-waits-for-nothing
> > > and his subsequent paper,
> > > http://www.rossbencina.com/static/writings/File_IO_ACMC2014_Bencina.pdf
> > >
> > > If you are not into asynchronous message passing and lock-free queueing
> > > then I’ll summarize the articles briefly:
> > >
> > > When engaging in file I/O (e.g reading from or writing to an audio file)
> > > do not use locks or blocking. He goes on to say that this can lead to
> > > priority inversion, unbound execution time and “scheduler paranoia”.
> > >
> > > This is all absolutely true in my experience in the audio jungle.
> > >
> > > Pd’s async file I/O objects (readsf~ and writesf~) use both locks and
> > > blocking via a mutex and the pthread_cond_signal and pthread_cond_init
> > > functions. Look at the source code file d_soundfile.c for more details.
> > > The gist of it is that these objects have two threads. One parent thread
> > > that sends the data to the dsp scheduler, and a child thread that grabs
> > > the data from the file, and subsequently the child signals the parent
> > > when it has more data.
> > >
> > > Based on Bencina’s paper, readsf~ and writesf~ could (should?) glitch and
> > > may not be real-time safe.
> > >
> > > My questions are:
> > >
> > > 1) Have I completely misunderstood d_soundfile.c and it is actually
> > > entirely safe. If so, why is it safe?
> > >
> > > 2) Why doesn’t Pd glitch more often when using these objects?
> > >
> > > 3) Does Pd need lock-free message queueing for such inter-thread
> > > communication?
> > >
> > > 4) Has anyone ever “broken” these objects or experienced glitching?
> > >
> > > Thanks for the extra brain power.
> > > -R
> > >
> > >
> > >
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