How to pass multiple arguments through g_idle_add()?

Question

I'm trying to use g_idle_add() with function that needs multiple arguments. Can I pass them just inline somehow or do I have to create a structure for this?

The main goal is to reduce memory consumption, everything else is secondary.

static gboolean checker(gpointer plugin, int toggle){
    ...  
    return FALSE;
}
g_idle_add(checker, ??? plugin, 0 ??? );

`typedef void* gpointer;` *An untyped pointer. gpointer looks better and is easier to use than void*.* Yuck... — this, Dec 20 '13 at 02:01
Maybe not exactly inline. Without creating a dedicated `struct`. I wouldn't like increasing memory consumption. — int_ua, Dec 20 '13 at 02:49
You can create a struct on the stack and pass it's address. Just make sure the struct doesn't go out of scope(global, static...). — this, Dec 20 '13 at 02:56
Edited the question with link to the code. I don't yet know how to create it on the stack, can you please add the code? — int_ua, Dec 20 '13 at 02:59
I don't think the line 43 is right since the seconde parametre is a pointer. I think you just call the function this way `g_idle_add((GsourceFunc)checker, (gpointer)plugin, (gpointer)0);` (you have to cast the arguments) — rullof, Dec 20 '13 at 03:15
**rullof**, I'm not sure it worked. Without enclosing arguments in parentheses it's `too few arguments` and with them there are only `warning: left-hand operand of comma expression has no effect`. Not sure if that will work as I expect. I've actually taken these parentheses from my Python knowledge, I'm beginner in C. — int_ua, Dec 20 '13 at 03:26
You have to create a structure. Passing more than one user_data argument won't work. — ptomato, Dec 20 '13 at 03:52

score 3 · Accepted Answer · answered Dec 20 '13 at 04:21

The function you pass to g_idle_add needs to have a signature matching the GSourceFunc type, which means it has to take exactly one pointer argument. You'll have to allocate a structure on the heap (NOT the stack as a commenter has suggested, that will only be valid for as long as the function creating it runs) containing the information you need. Something like this:

struct checker_arguments {
    gpointer plugin;
    int toggle;
};

static gboolean checker(gpointer data) {
    struct checker_arguments *args = data;
    /* Do stuff with args->plugin and args->toggle */
    g_slice_free1(args, sizeof(*args));
    return FALSE;
}

struct checker_arguments *args = g_slice_alloc(sizeof(*args));
args->plugin = plugin;
args->toggle = 0;
g_idle_add(checker, args);

Because you're concerned with memory consumption, I used slice allocation in this example rather than the normal heap allocation. Slice allocation is more efficient for objects of fixed size.

instead of g_slice_alloc/g_slice_free1, use g_slice_new() and g_slice_free() with the type you're allocating. it's easier to read, and clearer. — ebassi, Dec 20 '13 at 09:19

How to pass multiple arguments through g_idle_add()?

1 Answers1