G_idle_add from a worker thread

Platform
1

So I’m trying to use g_idle_add from a worker thread, and as soon as I do no more idle functions get called. At all. From any thread, including the one I just added. In my case I return FALSE from the function every time. And re-add it via g_idle_add as needed.

Context: v3.22.30 on windows. But I see the same behaviour on Linux. I currently can’t get a v3.24 build working on windows to check that.

All the calls to g_idle_add from the main GUI thread work fine. Up until I need to return data from a worker thread and then it all just stops. Is there something I need to do to allow g_idle_add to be called from a thread?

2

Actually after posting this I found this article and tried the suggested call. And guess what? It works as advertised. Even from my worker thread!

So yay I guess. This is the version that works for me:

g_main_context_invoke_full(NULL, G_PRIORITY_DEFAULT, (GSourceFunc)IdleWrapper, &idle, NULL);

3

To the best of my knowledge, that is equivalent to:

g_idle_add (IdleWrapper, &idle);

except when used in the main thread. It is documented that g_main_context_invoke will use an idle source in any case where it cannot call the function directly.

The linked article (canonical location) is warning against using g_idle_add and friends when you don’t want to use the default context. You are passing NULL as the context, which has the same result.

4

Well in practice it’s quite different. Which may just be bug(s) manifesting. So temporarily I’m not blocked, so care a lot less than this morning.

The context of what I’m trying to do is send events up to the GUI thread from workers. The event consists of a message int and a few parameters. I store them in a queue and then trigger an idle function to pass them off to various views in the GUI (which aren’t quite widgets but similar in concept). I was using client events in GTK2 but they went away.

5

Actually g_main_context_invoke_full is not working. It sometimes runs the callback in the same thread as the calling code. While means that GUI methods get called from a worker thread when instead the IdleWrapper callback should only ever be called on the main thread. I wish g_idle_add was just thread aware. It would make like so much easier.

6

g_idle_add does exactly what you want; it always adds the idle source to the GMainContext for the main thread (g_main_context_default()). If this isn’t working, there is a bug in your code.

7

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