Like with ecore_main_loop_thread_safe_call_sync() you can provide a callback to call inline in the mainloop, but this time with ecore_main_loop_thread_safe_call_async() the callback is queued and called asynchronously, without the thread blocking. The mainloop will call this function when it comes around to its synchronisation point. This acts as a "fire and forget" way of having the mainloop do some work for a thread that has finished processing some data and is read to hand it off to the mainloop and the thread wants to march on and do some more work while the main loop deals with "displaying" the results of the previous calculation.

//Compile with:
//gcc -o efl_thread_3 efl_thread_3.c -g `pkg-config --cflags --libs elementary`
#include <Elementary.h>
#include <pthread.h>

static Evas_Object *win = NULL;
static Evas_Object *rect = NULL;

struct info
{
   double x, y;
};

static void my_thread_mainloop_code(void *data);

static pthread_t thread_id;

// BEGIN - code running in my custom pthread instance
//
static void *
my_thread_run(void *arg EINA_UNUSED)
{
   double t = 0.0;

   // inside the pthread function lets loop forever incrementing a time point
   for (;;)
     {
        struct info *inf = malloc(sizeof(struct info));

        if (inf)
          {
             inf->x = 200 + (200 * sin(t));
             inf->y = 200 + (200 * cos(t));
             // now call a function in the mainloop and pass it our allocated
             // data that it will free when it gets it
             ecore_main_loop_thread_safe_call_async
                (my_thread_mainloop_code, inf);
          }
        // and sleep and loop
        usleep(1000);
        t += 0.02;
     }
   return NULL;
}
//
// END - code running in my custom pthread instance
static void
my_thread_new(void)
{
   pthread_attr_t attr;

   if (pthread_attr_init(&attr) != 0)
     perror("pthread_attr_init");
   if (pthread_create(&thread_id, &attr, my_thread_run, NULL) != 0)
     perror("pthread_create");
}

static void
my_thread_mainloop_code(void *data)
{
   struct info *inf = data;
   evas_object_move(rect, inf->x - 50, inf->y - 50);
   free(inf);
}

// on window delete - cancel thread then delete window and exit mainloop
static void
del(void *data EINA_UNUSED, Evas_Object *obj EINA_UNUSED, void *event_info EINA_UNUSED)
{
   elm_exit();
}

EAPI_MAIN int
elm_main(int argc EINA_UNUSED, char **argv EINA_UNUSED)
{
   Evas_Object *o;

   elm_policy_set(ELM_POLICY_QUIT, ELM_POLICY_QUIT_LAST_WINDOW_CLOSED);

   win = elm_win_util_standard_add("efl-thread-3", "EFL Thread 3");
   evas_object_smart_callback_add(win, "delete,request", del, NULL);

   o = evas_object_rectangle_add(evas_object_evas_get(win));
   evas_object_color_set(o, 50, 80, 180, 255);
   evas_object_resize(o, 100, 100);
   evas_object_show(o);
   rect = o;

   // create custom thread to do some "work on the side"
   my_thread_new();

   evas_object_resize(win, 400, 400);
   evas_object_show(win);

   elm_run();

   return 0;
}
ELM_MAIN()