A linux "cp" command equivalent that does read/write threading and buffer sharing for increased throughput?

Question

First, let me address your concerns.

I'm copying from one slow drive, to another (different) slow drive. Blocking for reads on one drive until I write to another leaves a lot of room for improvement.

I developed a small cpp/h file that does this for me. It improved speed in my use case by ~40%. https://github.com/pauldotknopf/AsyncStreamCopyCPP/blob/master/examples/main.cpp

I'd like to know if there is something equivalent, but as a command. Preferably one that is similar to how the "cp" command operates.

# Use async read/write threads and shared/re-used buffers between the two.
cp /slowdrive1/file1.txt /slowdrive2/file2.txt