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use parking_lot::RwLock;
const CHUNK_LEN: usize = 16;
pub struct Arena<T> {
chunks: RwLock<Vec<Vec<T>>>,
}
impl<T> Arena<T> {
pub fn new(&self) -> Arena<T> {
Arena {
chunks: RwLock::new(vec![Vec::with_capacity(CHUNK_LEN)]),
}
}
pub fn push(&self, value: T) -> usize {
let mut guard = self.chunks.write();
let mut idx = (guard.len() - 1) * CHUNK_LEN;
let chunk = {
if guard.last().unwrap().len() == CHUNK_LEN {
guard.push(Vec::with_capacity(CHUNK_LEN));
}
guard.last_mut().unwrap()
};
assert!(chunk.len() < chunk.capacity());
idx += chunk.len();
chunk.push(value);
idx
}
pub fn get(&self, idx: usize) -> &T {
let chunk_idx = idx / CHUNK_LEN;
let chunk_off = idx - chunk_idx * CHUNK_LEN;
let guard = self.chunks.read();
let value = &guard[chunk_idx][chunk_off];
unsafe {
// We are careful to not move values in chunks,
// so this hopefully is safe
::std::mem::transmute::<&T, &T>(value)
}
}
}
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