How to send user_data with gtk signals in loop

Question

I have signals "make" and "send" registered in core class in main thread. I call call_make() from user class in same thread. call_make() will do some work and fetch some data from worker thread and after return it will emit signal "make".

This is code of user class

struct my_struct{
   int cur_make_id;
   int cur_send_id;    //there may be many id's if multiple signals
}

void on_send_cb(core, gpointer data){
   my_struct *user_data = (my_struct *) data;
   printf("cure_make_id %d", user_data->cur_make_id);   \\ this prints "4" everytime  
   printf("cure_send_id %d", user_data->cur_send_id);   \\ this prints "2" everytime  
}

void on_make_cb(core, gpointer data){
   my_struct *user_data = (my_struct *) data;
   printf("cure_make_id %d", user_data->cur_make_id);   \\ this prints "4" everytime  
   for(int index=0;index<3;index++){
       call_send();
       user_data->cur_send_id = index;
       g_signal_connect(core, "send", G_CALLBACK(on_send_cb), user_data );
   }     
}

void function(){
   my_struct *user_data = g_malloc0(sizeof(my_struct));
   for(int index=0;index<5;index++){
       call_make();
       user_data->cur_make_id = index;
       g_signal_connect(core, "make", G_CALLBACK(on_make_cb), user_data );
   }
}

I get wrong cur_make_id and cur_send_id for all signals (getting last index of for loop)

I know signal_emit and connect delayed and for loop moved forward. I want to know how can I share this user_data to callback so that I can know that this callback is for which index?

(for simplicity I made these call_make() api's, I can't change arguments of api's)

I have changed this code for simplicity. 'core is class from where this signal emits. Yes code compiles I get signals as well. I just want to know how to share user_data. I can't share full code — Its me
"I get wrong cur_make_id and cur_send_id for all signals (getting last index of for loop)" You know that you only allocate one structure holding one index and use it in your loop, do you? BTW: How and when do you send your signals and when are your callbacks called? — Gerhardh

Gerhardh Gerhardh · Accepted Answer · 2020-05-29T09:44:57

Assuming you are only talking about the user_data provided during connecting the callback, you have wrong memory allocation:

void function(){
   my_struct *user_data = g_malloc0(sizeof(my_struct));
   for(int index=0;index<5;index++){
       call_make();
       user_data->cur_make_id = index;
       g_signal_connect(core, "make", G_CALLBACK(on_make_cb), user_data );
   }
}

In this function you have only 1 single block of memory that is passed to all connected callback functions. Whenever the callbacks are called, they will see whatever was written there last. In your case this will be index=4.

To provide different data for different handlers, you actually need to allocate different data:

void function(){
   for(int index=0;index<5;index++){
       my_struct *user_data = g_malloc0(sizeof(my_struct));
       call_make();
       user_data->cur_make_id = index;
       g_signal_connect(core, "make", G_CALLBACK(on_make_cb), user_data);
   }
}

If you also have problems providing data from the function triggering the signal, you need to show more code.

How to send user_data with gtk signals in loop

1 Answers