Function block_on 

pub fn block_on<F: Future>(future: F) -> F::Output

Block on a future using an isolated Tokio runtime with one async worker.

The future is driven on the calling thread. Spawned async helpers use one additional worker, so they can progress while that thread blocks. Tokio may create further threads for spawn_blocking, filesystem or DNS operations. The worker count is explicit and independent of TOKIO_WORKER_THREADS.