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.