Cross thread call a.k.a run on main/UI thread from other thread without dependencies needed

I'm on some c++ mobile product, but I need my apps main thread is still running without any blocking when doing some heavy work on the background thread and run back on main thread. But I realized there is no runOnMainThread/runOnUIThread in c++ thread api. I trying to figure it out the issue and found that need to depend library, or create your own thread event queue. Although it is good, but i am thinking to have a behavior which can runOnUIThread.