pub fn new() -> Self {
        let pool_size = thread::available_parallelism().map_or(1, |p| p.get());
        Self { pool_size, stack_size: 0, name_prefix: None, after_start: None, before_stop: None }
    }
Create a default thread pool configuration.

See the other methods on this type for details on the defaults.
futures-executor/src/thread_pool.rs