[visionegg] Re: VisionEgg and Threads?
- From: Andrew Straw <astraw@xxxxxxxxxxx>
- To: visionegg@xxxxxxxxxxxxx
- Date: Thu, 30 Aug 2007 14:24:04 -0700
Thomas Schreiner wrote:
> If we do so by calling p.go() from inside a python
> thread, the start frame of the graphical presentation is displayed but
> is not updating at all.
That's not surprising -- it sounds like you've setup OpenGL from the
main thread but are then calling it from another thread. I think (but
I'm not completely sure) that OpenGL implementations are generally not
able to be called this way. You'd have to setup the VE entirely from the
second thread.
If we call p.go() from the main part of the
> program and leave out threading, it works perfectly, but it blocks our
> other python threads - they just don't run.
This is somewhat surprising to me, but I have some ideas. Firstly, is
the VE running without vsync? If so, it could be running full out,
drawing thousands of frames per second and dominating the CPU. (With the
Python GIL, this probably wouldn't be helped by having a multi-core
system.) Secondly, it is entirely possible that the call to
swap_buffers() is not releasing the GIL. So, even though the CPU is
doing nothing, your other Python thread is prevented from running. If
this is the case, we need to figure out how to release the GIL. (Not
hard but will require modifying the C code that runs at that point.) If
the issue is one of these 2 possibilities, the test will be whether the
CPU is maxed out. Are you using PyOpenGL 2 (SWIG-based) or 3 (ctypes-based)?
BTW, I've done just what I understand you want to do quite well with
only a single thread -- typically between frame draws I query the data
acquisition buffer, which is big enough to accommodate the data coming
in. Without vsync on and with a simple visual stimulus, I can query the
card and redraw the frames on the order of 1000 fps with a 1.5 GHz
Celeron computer. In this configuration, I've found it easier to use the
VE without the FlowControl module.
Cheers!
Andrew
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