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use std::{
collections::VecDeque,
ops::{Deref, DerefMut},
sync::{Condvar, Mutex},
};
pub struct Pool<T> {
items: Mutex<VecDeque<T>>,
value_returned: Condvar,
}
impl<T> Pool<T> {
pub fn new(items: impl IntoIterator<Item = T>) -> Self {
Pool {
items: Mutex::new(items.into_iter().collect()),
value_returned: Condvar::new(),
}
}
pub fn take(&self) -> Returnable<T> {
let mut lock = self.items.lock().unwrap();
loop {
if let Some(value) = lock.pop_front() {
return Returnable {
value: Some(value),
pool: self,
};
}
lock = self.value_returned.wait(lock).unwrap();
}
}
fn return_(&self, value: T) {
self.items.lock().unwrap().push_back(value);
}
}
pub struct Returnable<'p, T> {
value: Option<T>,
pool: &'p Pool<T>,
}
impl<'p, T> Drop for Returnable<'p, T> {
fn drop(&mut self) {
self.pool.return_(self.value.take().unwrap());
self.pool.value_returned.notify_one();
}
}
impl<'p, T> Deref for Returnable<'p, T> {
type Target = T;
fn deref(&self) -> &Self::Target {
self.value.as_ref().unwrap()
}
}
impl<'p, T> DerefMut for Returnable<'p, T> {
fn deref_mut(&mut self) -> &mut Self::Target {
self.value.as_mut().unwrap()
}
}