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 > > > > > > > > > > > > _______________________________________________ > > > [email protected] mailing list > > > UNSUBSCRIBE and account-management -> > > > http://lists.puredata.info/listinfo/pd-list > > > > > > > > > > > > > > _______________________________________________ > > > [email protected] mailing list > > > UNSUBSCRIBE and account-management -> > > > http://lists.puredata.info/listinfo/pd-list > > > > > > _______________________________________________ > > [email protected] mailing list > > UNSUBSCRIBE and account-management -> > > http://lists.puredata.info/listinfo/pd-list > > > > > > > > > > > > > _______________________________________________ > [email protected] mailing list > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list _______________________________________________ [email protected] mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list
