Function parallel_map 

pub async fn parallel_map<F, T, R>(
    pool: &ComputePool,
    items: Vec<T>,
    f: F,
) -> Result<Vec<R>>
where
    F: Fn(T) -> R + Sync + Send + 'static,
    T: Send + 'static,
    R: Send + 'static,

Execute multiple functions in parallel using scope