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use std::mem;
use std::ops::{
Deref, DerefMut,
};
use std::sync::{
Mutex, MutexGuard,
};
pub struct Pool<T> {
inner: Vec<Mutex<T>>
}
impl<T> Pool<T> {
pub fn new<F>(cap: usize, init: F) -> Pool<T>
where F: Fn() -> T {
let mut inner = Vec::with_capacity(cap);
for _ in 0..cap {
inner.push(Mutex::new(init()));
}
Pool {
inner
}
}
pub fn pull(&self) -> Option<Reusable<T>> {
for entry in &self.inner {
let entry_guard = match entry.try_lock() {
Ok(v) => v,
Err(_) => { continue; }
};
return Some(Reusable {
data: entry_guard,
});
}
None
}
}
impl Pool<Vec<u8>> {
pub fn count(&self) -> u64 {
let mut count = 0 as u64;
for entry in &self.inner {
let entry_guard = match entry.try_lock() {
Ok(v) => v,
Err(_) => { continue; }
};
count += entry_guard.len() as u64;
}
count
}
}
pub struct Reusable<'a, T> {
data: MutexGuard<'a, T>,
}
impl<'a, T> Reusable<'a, T> {
pub fn detach(&mut self, replacement: T) -> T {
mem::replace(&mut self.data, replacement)
}
pub fn attach(&mut self, data: T) -> T {
mem::replace(&mut self.data, data)
}
}
impl<'a, T> Deref for Reusable<'a, T> {
type Target = T;
fn deref(&self) -> &Self::Target {
self.data.deref()
}
}
impl<'a, T> DerefMut for Reusable<'a, T> {
fn deref_mut(&mut self) -> &mut Self::Target {
self.data.deref_mut()
}
}
#[cfg(test)]
mod tests {
use std::sync::Arc;
use super::*;
#[test]
fn round_trip() {
let pool: Arc<Pool<Vec<u8>>> = Arc::new(Pool::new(10, || Vec::with_capacity(1)));
for _ in 0..10 {
let tmp = pool.clone();
std::thread::spawn(move || {
for i in 0..1_000_000 {
let mut reusable = tmp.pull().unwrap();
if i % 2 == 0 {
let mut vec = reusable.detach(Vec::new());
vec.push(i as u8);
reusable.attach(vec);
} else {
reusable.push(i as u8);
}
}
});
}
std::thread::sleep_ms(3000);
assert_eq!(pool.count(), 10_000_000)
}
}