Hello everyone,I have two problems

I encountered two problems in the developing of multi video system with the SDL2.Hope to get your helping platform—win7 64 ultimate VS2008 sdl2.0 direct3d9—:
1, my every video screen in a separate thread to do video playing, each corresponding to a Texture, multiple threads share a Render, I want to every thread asynchronous execution of the SDL_RenderCopy, but then perform the SDL_RenderPresent after the SDL_RenderCopy is executed when there will be multithread synchronization problem (SDL_RenderPresent is the entire screen to submit, Direct3DDevice9:: Present has Rect parameters)
2, when I press win+l or ctrl+alt+del key into the lock screen mode, then back to the desktop, the SDL_Window will Disappeared.