pub trait i_threadpool {
// Required methods
fn spawn(&mut self) -> bool;
fn terminate(&mut self) -> bool;
fn withdraw(&mut self) -> Option<u64>;
fn deposit(&mut self, handle: u64) -> bool;
fn query_total(&mut self) -> u64;
fn query_available(&mut self) -> u64;
fn query_unavailable(&mut self) -> u64;
}