gtk_events_pending() returns FALSE with events still pending

Question

I'm working on an application that has a start and stop button. These buttons block the UI, and for various reasons, I can't spawn a thread.

I've been showing a working screen when these buttons are pressed, using:

while (gtk_events_pending()) gtk_main_iteration();

which ensures that the working screen is loaded before the start/stop operations begin.

I've recently upgraded to GTK+ 3.8.6, and it seems that gtk_events_pending() is now broken. Now, sometimes the window shows, but the image in the window isn't there. Sometimes the window doesn't even show.

The function in question looks like:

gtk_widget_show(working_screen);
while (gtk_events_pending()) gtk_main_iteration();

long_running_blocking_function();

If I do something like:

int busy_wait = 0;
gtk_widget_show(working_screen);
while (gtk_events_pending() || busy_wait < 5) 
{
    gtk_main_iteration();
    if (!gtk_events_pending()) ++busy_wait;
}

long_running_blocking_function();

...it works fine. However, I know it's only a matter of time until the busy_wait needs to be longer so I'd like to find a better answer. Has anybody experienced this issue? Does anybody have any ideas about how I might work around it?

Answer 1

Try g_main_context_pending(NULL) and g_main_context_iteration(NULL,FALSE) instead of gtk_events_pending(), the later is deprecated.

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It could be a timing issue that kicks in (it oculd be that your loop kicks in before any events are registered to the mainloop, and thus instantly exits) - but this is just wild guessing due to lack of code.

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The break condition is also wrong, you do not want to exit as soon as all events are processed at a specific point of time, you want to continue until long-run-ops are done. That means you need to signal when your operation is done, check that flag in the loop you currently use and use blocking mode of the *_iteration(...)