Re: Proper way to provide gtk+ app with asynchronous data?

["Dmitry M. Shatrov" <zzidre mail ru>]

I've found that with the third thread I can do a very nice thing: to 
filter data so that  (my "data" is consequent tool positions, i. e. 
vectors): if during drawing of the last vector there appeared, say, 10 
more vectors to draw, I can throw away first 9 and draw only the last, 
the most fresh one. In my case it would be helpful, especially if it'll 
be drawn in slow 3D.

So, 3 threads.

Thanks all for help!

NavEcos wrote:

> You can use a pipe and use 3 threads.
>
> Use one thread for the "main" gtk loop - this will the thread the calls
> gtk_main()
> Use one thread to acquire data and send the data through a pipe
> Use one thread to do the updates to the screen asynchrnously - it will get
> its data via a pipe.
>
> It's been a while since I've use pipes, but as I recall (dimly) it's pretty
> straighforward, just do a "man 2 pipe"
>
> Another note about using threads with gtk - do NOT do this in your
> asynchronous thread:
>
> for (;;)
> {
>  gdk_threads_enter()
>  // wait for data (!)
>  // update screen
>  gdk_threads_leave();
> }
>
> do this instead
>
> for (;;)
> {
>  // wait for data (don't block between gdk_threads_enter & leave)
>  gdk_threads_enter()
>  // update screen
>  gdk_threads_leave();
> }
>
> If you do the first one, you'll lock up your application update while data
> is waiting to be received.
>
> Do not waste a lot of time trying to do gdk_threads_enter() and ...leave()
> in lots of places to minimize the time spent in the gdk_threads_enter() and
> ...leave() areas - do NOT think of it as a critical section another words.
> Keep it simple!
>
> Another fun thing - if you try to set a breakpoint in gdb where
> gdk_threads_enter() has been entered, it will lock up your entire screen
> sometimes.  It pays to have two X11 sessions or 2 machines: OR better yet:
> you can get around this though using Xvnc - use a virtual X11 display.  Xvnc
> is part of TightVNC, do a man on vncviewer and vncserver.  There are
> vncviewers available for Windows, and let me tell you, it's great.
>
> Good luck, it's not a lot of fun to deal with threads in my opinion with
> GTK.
>
> -Rich
>
> P.S. If you've not played with it, try fooling around with TightVNC a bit.
> It's a wonderful little program and extremely useful, and the best kept
> secret of Linux in my opinion.  With it, we run 5 users on a single machine,
> and use dumb terminals with either Knoppix or Windoze to connect.  It
> greatly reduces our IT headaches, and saved us lots of money.
>  
Well, when it'll be about money for me, I'll think of it, of cource.