pub trait Balancer:
Send
+ Sync
+ 'static {
// Required method
fn pick<'a>(&self, ctx: &'a BalanceCtx<'a>) -> Option<usize>;
// Provided methods
fn on_start(&self, _event: &StartEvent<'_>) { ... }
fn on_result(&self, _event: &ResultEvent<'_>) { ... }
}