Re: How to add a callback that will be called each time when the event queue becomes empty

[Gang Chen <gang chen cn gmail com>]

Because the idle callback always returns TRUE, the idle callback is called again and again, and CPU usage is 100%.

The idle callback doesn't do any heavy processing.

Regarding this problem, doing central updating when idle is simpler than using signals to update.

2013/7/20 Jasper St. Pierre <jstpierre mecheye net>

Low-priority idles *are* called every time the event queue is empty. Which could happen quite a lot when the application isn't really doing anything else.

I don't know why your idle is causing 100% CPU usage, though. You're not doing any heavy processing in there, right? If you recalculate the state, and that causes set_sensitive to be called with the same value it was before, we won't redraw the UI or anything.

If the idle indeed is doing heavy processing, then the only thing you can do is to call it when a state change happens somewhere. Yes, there can be lots of state changes, but that's what entire signal system is for. Perhaps also look at g_object_bind_property / properties / notify::prop signals?

On Fri, Jul 19, 2013 at 3:45 PM, Gang Chen <gang chen cn gmail com> wrote:

Richard,

The UI elements are GTK actions whose sensitivity states are related to the states of the application. There are many possibilities that may change the sensitivity. If I update UI elements whenever necessary, I need to write too much code doing update. I prefer writing one function that updates all UI elements according to the current states. And I need to call that function when idle. This approach is simpler and cleaner.

Thanks,
Gang

2013/7/20 richard boaz <ivor boaz gmail com>

let's step back one second.

your description implies that it is not possible for your UI to be directly aware of the events that require follow-on updates to the UI's widgets.  

but i don't understand this.  can you explain a little more how/why this makes sense on a design level?  what exactly happens that means the UI widget states are out-of-date and need to be updated?

ideally, your UI should be aware of any state changes requiring a widget update, these being either internal or external in origin.  and then once a state change occurs, invoke your widget updates accordingly.

richard

On Thu, Jul 18, 2013 at 12:11 AM, Gang Chen <gang chen cn gmail com> wrote:

Hi everyone,

The background is that I need to update the sensitivity of UI elements when proper. I tried to do it in a low priority idle callback that is running forever. But that will cause 100% CPU usage. So I'd like to do it in a callback that is called only once each time when the event queue becomes empty. Do you have any idea? Or is there any better approach to updating UI elements?

Thanks,

Gang

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  Jasper