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|
//! This hack allows a db tree to keep in RAM a counter of the number of entries
//! it contains, which is used to call .len() on it. This is usefull only for
//! the sled backend where .len() otherwise would have to traverse the whole
//! tree to count items. For sqlite and lmdb, this is mostly useless (but
//! hopefully not harmfull!). Note that a CountedTree cannot be part of a
//! transaction.
use std::sync::{
atomic::{AtomicUsize, Ordering},
Arc,
};
use crate::{Result, Tree, TxError, Value, ValueIter};
#[derive(Clone)]
pub struct CountedTree(Arc<CountedTreeInternal>);
struct CountedTreeInternal {
tree: Tree,
len: AtomicUsize,
}
impl CountedTree {
pub fn new(tree: Tree) -> Result<Self> {
let len = tree.len()?;
Ok(Self(Arc::new(CountedTreeInternal {
tree,
len: AtomicUsize::new(len),
})))
}
pub fn len(&self) -> usize {
self.0.len.load(Ordering::Relaxed)
}
pub fn is_empty(&self) -> bool {
self.len() == 0
}
pub fn get<K: AsRef<[u8]>>(&self, key: K) -> Result<Option<Value>> {
self.0.tree.get(key)
}
pub fn first(&self) -> Result<Option<(Value, Value)>> {
self.0.tree.first()
}
pub fn iter(&self) -> Result<ValueIter<'_>> {
self.0.tree.iter()
}
// ---- writing functions ----
pub fn insert<K, V>(&self, key: K, value: V) -> Result<Option<Value>>
where
K: AsRef<[u8]>,
V: AsRef<[u8]>,
{
let old_val = self.0.tree.insert(key, value)?;
if old_val.is_none() {
self.0.len.fetch_add(1, Ordering::Relaxed);
}
Ok(old_val)
}
pub fn remove<K: AsRef<[u8]>>(&self, key: K) -> Result<Option<Value>> {
let old_val = self.0.tree.remove(key)?;
if old_val.is_some() {
self.0.len.fetch_sub(1, Ordering::Relaxed);
}
Ok(old_val)
}
pub fn compare_and_swap<K, OV, NV>(
&self,
key: K,
expected_old: Option<OV>,
new: Option<NV>,
) -> Result<bool>
where
K: AsRef<[u8]>,
OV: AsRef<[u8]>,
NV: AsRef<[u8]>,
{
let old_some = expected_old.is_some();
let new_some = new.is_some();
match self.0.tree.db().transaction(|mut tx| {
let old_val = tx.get(&self.0.tree, &key)?;
if old_val.as_ref().map(|x| &x[..]) == expected_old.as_ref().map(AsRef::as_ref) {
match &new {
Some(v) => {
tx.insert(&self.0.tree, &key, v)?;
}
None => {
tx.remove(&self.0.tree, &key)?;
}
}
tx.commit(())
} else {
tx.abort(())
}
}) {
Ok(()) => {
match (old_some, new_some) {
(false, true) => {
self.0.len.fetch_add(1, Ordering::Relaxed);
}
(true, false) => {
self.0.len.fetch_sub(1, Ordering::Relaxed);
}
_ => (),
}
Ok(true)
}
Err(TxError::Abort(())) => Ok(false),
Err(TxError::Db(e)) => Err(e),
}
}
}
|
