Re: Event loop hangup when using TimeoutSource and IdleSource

[Robert Pearce <rob bdt-home demon co uk>]

Hi Jim,

On Thu, 24 Sep 2009 13:31:53 -0400 you wrote:

> I am trying to create a pretty simple gtkmm application. The purpose  
> of the application is to display the status of an attached device and  
> to also send commands to the device to control it. The device is  
> connected to the computer via a serial port and abstracted by a  
> library API that I also wrote. My gtkmm application is designed to  
> poll the device for various status via one function that gets called  
> every 100 ms via a TimeoutSource.

That's not very different from an application I'm developing.
 
<snip> 

> The weird part is that this "loop" of calling the updateEMSStatus()  
> function via the TimeoutSource hangs randomly. It sometimes will hang  
> after one cycle through (meaning through every status get request that  
> fires in 1 second, 2 seconds, 5 seconds, etc)), and sometimes it'll do  
> several cycles through with the timer returning hundreds of times.

I seem to recall having similar problems early on, but I can't remember the details.

> It  
> doesn't seem to get stuck in any of my functions, it seems to be the  
> Glib event loop that is getting stuck because my GUI becomes  
> completely unresponsive. Any thoughts?

Well one thought is that that is an unsafe deduction. The glib event loop is single-threaded and needs everything it calls to return in a timely manner. If one of your functions hangs, whether a command sender or a callback, the result will be to lock up the glib event loop.

> Am I not using the Idlesource  
> in a proper manner?

Possibly, but your code snippet didn't look wrong.

> Is this a resource leak somehow? 

Unlikely - it's too quick

> How would I go  
> about debugging where in the Glib event loop it might be hanging at?
> 
With a debugger? Or possibly by scattering a few "entering this", "leaving that" debug messages around.

How are you handling the returned serial data? Are you polling? Calling select? Using read? Using a separate thread? Relying on glib via a Glib::IOChannel (which is the method I use)?


Rob