Re: Refreshing of the text

[John Cupitt <john cupitt ng-london org uk>]

Durie, James wrote:
> > - Make a background thread to do the sniffing with 
> > g_thread_create(). Make
> >  a pipe, and have the background thread write its results to 
> > the pipe.
> >  Do gtk_input_add_full() to make your foreground thread wake 
> > up when things
> >  are written to the pipe. When stuff arrives, update the screen.
>
>
> Why have a pipe.
> Why not have an area of memory where the data is stored. A semaphore to
> avoid the two threads accessing at the same time and a dirty flag.
>
> The sniffer thread updates this area every time a new packet comes in and
> sets the dirty flag.
>
> The gui thread has a timer with a callback which reads this area and updates
> the display and resets the dirty flag.
>
> It may be that several packets come up before the display updates and it
> might be that none come in. Obviously the display only needs to update if
> the dirty flag is set.

Yes, also a good solution. I usually use a pipe because you don't need a mutex, you don't need the polling in the GUI thread, and you won't miss updates if you're too slow. 

You're also right that for a (potentially) high-volume thing like a packet sniffer there will have to be some mechanism for throwing away data when it's coming in faster than the GUI can repaint. For the pipe implementation, I guess the GUI would have to read-until-empty on the pipe when it woke up, then just use the last packet to update the screen.

John