C++ GeoClue g_object_unref: assertion 'G_IS_OBJECT (object)' failed

Question

So I recently tried to try out GeoClue for one of my Raspberry Pi projects, but I got stuck on using gclue-simple(). Running gclue_simple_new seemed to be fine, but when I was trying to pick up the pointer with gclue_simple_new_finish(), the program gives me a runtime error:

(process:37607): GLib-GIO-CRITICAL **: 16:26:33.873: g_async_result_get_source_object: assertion 'G_IS_ASYNC_RESULT (res)' failed

(process:37607): GLib-GIO-CRITICAL **: 16:26:33.873: g_async_initable_init_finish: assertion 'G_IS_ASYNC_INITABLE (initable)' failed

(process:37607): GLib-GObject-CRITICAL **: 16:26:33.873: g_object_unref: assertion 'G_IS_OBJECT (object)' failed

The code for the program is here:

#include <cstdlib>
#include <iostream>

#include <gclue-simple.h>

void geoclue_callback (GObject* srcObj, GAsyncResult* result, void* userData); 

int main(){
    std::cout << "Program started." << std::endl; 
    
    const char* DESKTOP_ID = "desktop1"; 
    GClueAccuracyLevel accuracy = GCLUE_ACCURACY_LEVEL_CITY; 
    GCancellable* cancellablePtr = NULL; 
    GAsyncReadyCallback callback = geoclue_callback; 
    //gpointer is like void pointer. 
    gpointer usrDataPtr; 

    std::cout << "Variables declared." << std::endl; 

    gclue_simple_new(
        DESKTOP_ID, 
        accuracy, 
        cancellablePtr, 
        callback, 
        usrDataPtr
    ); 

    std::cout << "geoclue service started." << std::endl; 

    GClueSimple* gclueServicePtr; 
    GAsyncResult* rstPtr; 
    GError** errsPtr; 
    //This part here causes runtime error. 
    gclueServicePtr = gclue_simple_new_finish(rstPtr, errsPtr); 

}

void geoclue_callback (GObject* srcObj, GAsyncResult* result, void* userData) { 
    //Callback function for when Geoclue comes up with something
    std::cout << "Results Ready." << std::endl; 
}

I've only just gotten into geoclue and I have no previous experience with anything related to gtk or the GNOME project, so I'm probably missing something obvious.

Thanks!

Answer 1

The callback is not to tell you that some results are ready, it’s to tell you that your GClueSimple* object has been created. You need to call gclue_simple_new_finish() from inside callback, not before. And you need to pass the GAsyncResult *result into it, plus a pointer to a GError *error = NULL initialised error.

gclue_simple_new_finish() may return NULL (and a GError object in the error pointer you gave it) if initialisation failed.