[PD] [GEM-dev] Timing and PD....
ben at ekran.org
Thu Oct 30 17:28:53 CET 2008
I'll try and work on some test patches, right now I'm trying hard to get
an installation ready, and these issues turned out to be a large
I suppose I'm doing lots of processing that may be unusual, like:
Grab an image from video device
put the image in a buffer for each frame
send the image in the buffer to a second buffer on each bang from a metro.
pix_share the image in the second buffer
send a bang to tell second pd instance to pix_dump.
turn off the metro.
pix_dump (640x480 GRAY) to ann_som in a second thread
netreceive the winning BMU
use that BMU as the index in which the image has saved in a third buffer.
turn the metro back on.
I'm not thinking pix_share should do sync!! But I feel the need for some
infrastructure better than trigger for complex timing problems like
those I'm having.
I'm still debugging my patch, but adding a whole lot of arbitrary delays
(150ms) are being used to get PD to wait a little bit before accessing
the image in a buffer once it has been written.
Seems the safest way...
I remember Cyrille did mention needing to use these delays to make
things work. I had to use them in parts of pixelTANGO also (when a
message gets passed through many objects and many routes it takes time...)
As I have not noticed any render blocks with pix_buffer stuff, can I
assume it uses a thread like pix_image and so on? I think a "done" bang
would be really useful there.
I also had issues with things like pix_histo, where I would try and save
the hist, but the hist had not changed for the new pix_buffer_read
frame, just because the delay was slower than t b b delay.
Are cyrille and I the only ones seeing these kinds of issues?
Thanks for the comments.
chris clepper wrote:
> Internally, objects like pix_image and pix_film set flags for whether an
> image is new or not. This tells other objects to update. Perhaps a
> generic object (pix_info ?) can output when that flag is set.
> pix_share is a little different than image loading as it just dumps a
> new image into the gemlist each frame. It is not designed to do sync
> between instances of pd, but rather to be an asynchronous way to
> distribute processing. Making it sync would remove the performance gains.
> On Thu, Oct 30, 2008 at 9:32 AM, Hans-Christoph Steiner <hans at eds.org
> <mailto:hans at eds.org>> wrote:
> I agree. I think for any indeterminate operation, like anything in a
> separate thread, there should be a bang when that operation is
> complete. That way you can guarantee that things are ready when you
> run a process. If you want to make sure that things will be there on
> time, then these threaded/indeterminate operations should run well in
> advance. Using guesswork and delays is not a real solution...
> On Oct 30, 2008, at 4:25 AM, cyrille henry wrote:
> > helo,
> > i'm also having this kind of problem.
> > specially when loading a picture in pix_image.
> > i think the best would be the have a bang when things are ready...
> > C
> > B. Bogart a écrit :
> >> Hey all,
> >> I'm having more and more problems with sync in PD. By sync I mean
> >> that
> >> parts of my patches have processing delays that mess up timing. In
> >> general I've been using buffers and delays to keep things working.
> >> This approach is not very scalable.
> >> I find myself using the "timer" object all the time to see if
> >> there is a
> >> processing delay I have to worry about. That is in cases where
> >> there is
> >> a bang saying an operation is done.
> >> Two examples I'm working on now (in Gem):
> >> First there is a delay between sending a message and the
> >> pix_buffer to
> >> store, and then again for pix_buffer_read to read the pixels. The
> >> delay
> >> is long enough that trigger does not work, there needs to be a
> >> delay to
> >> make sure the image in the buffer is the right one. (sometimes as
> >> much
> >> as 200ms)
> >> A second example is that I'm using pix_share and and second PD
> >> instance
> >> to offload some CPU usage. Making sure the image sent to that PD
> >> instance and the image received later in the chain is difficult.
> >> I'm not writing for specific advice, hence the generalities, but
> >> wanted
> >> to start a discussion on the issue.
> >> What is the long-term solution for PD to solve these issues?
> >> Should all
> >> objects that introduce a delay send a bang when they are complete?
> >> (for
> >> example pix_buffer? Of course an additional delay occurs when when
> >> the
> >> pix_buffer is written to memory and when it gets to the gfx card for
> >> display.
> >> I'm banging my head over these issues a lot lately and wonder if
> >> there
> >> is a better approach.
> >> Back to attempting kludging a solution.
> >> .b.
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