CUDA Memory Copy Synchronization Problem in Multiple Processes

Currently I have a PC with 3 GPUs.

I created a parent process and created two child processes.

Each subprocess uses a different GPU to copy the GPU image.

By the way, I noticed that when copying an image using cudaMemcpy,

I use the GPU used to draw the screen.

Please let me know how to allow different processes

to successfully synchronize the GPU memory copy.

Is cudaSetDevice a function that can only be used within one process?