Re: deadlock

["Brian J. Tarricone" <bjt23 cornell edu>]

Dirk Huenniger wrote:

> Hello everybody,
> My name is Dirk, I'm writing a control programm for a 1m telescope in
> Germany. The current status of the device is periodically displayed in 
> GTK using a thread. When the user clicks the quit butten a callback 
> routine is
> started. At the same time  my thread does a gtk_threads_enter(). But 
> it cannot enter because the callback is running so it waits inside the 
> gtk_threads_enter
> routine. My callback routine askes the thread to quit and waits for that
> to happen. But the thread cannot react because it is waiting inside 
> gtk_threads_enter(). So everything is hanging now.
Yeah, this is a somewhat yucky situation.  The best way (that I've 
found) is to call g_idle_add() from the thread (instead of locking Gdk 
and doing your processing there), and handle the processing in the idle 
function (which runs in the main thread).  You still need 
gdk_threads_enter/leave() in the idle function, but the deadlock 
condition with the thread quitting is no longer there.  Of course, this 
means that the GUI processing occurs somewhat later - when the glib 
mainloop processes idle functions - but it usually isn't a big deal, 
though I don't know how time-sensitive your display needs to be.
   -brian