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|
use std::hash::{
Hash,
Hasher,
};
use std::ptr;
use std::sync::atomic::{
AtomicPtr,
Ordering,
};
use crate::arena::LocalArena;
struct FNV1a {
state: u64,
}
impl FNV1a {
const OFFSET_BASIS: u64 = 0xCBF29CE484222325;
const PRIME: u64 = 0x00000100000001B3;
fn new() -> Self {
return Self {
state: Self::OFFSET_BASIS,
};
}
}
impl Hasher for FNV1a {
fn write(&mut self, bytes: &[u8]) {
for &b in bytes {
self.state ^= b as u64;
self.state = self.state.wrapping_mul(Self::PRIME);
}
}
fn finish(&self) -> u64 {
return self.state;
}
}
pub struct HTrieNode<K, V>
where
K: Copy + Eq + Hash,
{
sub: [AtomicPtr<HTrieNode<K, V>>; 4],
key: K,
val: AtomicPtr<V>,
}
impl<K, V> HTrieNode<K, V>
where
K: Copy + Eq + Hash,
{
fn new(key: K, valptr: *mut V) -> Self {
return Self {
sub: [
AtomicPtr::new(ptr::null_mut()),
AtomicPtr::new(ptr::null_mut()),
AtomicPtr::new(ptr::null_mut()),
AtomicPtr::new(ptr::null_mut()),
],
key,
val: AtomicPtr::new(valptr),
};
}
}
#[derive(Debug)]
pub struct HTrie<K, V>
where
K: Copy + Eq + Hash,
{
root: AtomicPtr<HTrieNode<K, V>>,
}
impl<K, V> HTrie<K, V>
where
K: Copy + Eq + Hash,
{
pub fn new() -> Self {
return Self {
root: AtomicPtr::new(ptr::null_mut()),
};
}
/// Lock-free insert into the hash-trie.
///
/// Returns `None` if the key was newly inserted.
/// Returns `Some(val)` with the previous value if the key already
/// existed.
pub fn insert(&self, key: K, val: V, arena: &LocalArena) -> Option<V> {
let mut h = {
let mut h = FNV1a::new();
key.hash(&mut h);
h.finish()
};
let mut m = &self.root;
let valptr = arena.alloc(val);
loop {
let mut n = m.load(Ordering::Acquire);
if n.is_null() {
let mark = arena.mark();
let node = arena.alloc(HTrieNode::new(key, valptr));
match m.compare_exchange(
ptr::null_mut(),
node as *mut HTrieNode<K, V>,
Ordering::Release,
Ordering::Acquire,
) {
Ok(_) => {
return None;
},
Err(ptr) => {
arena.restore(mark);
n = ptr;
},
}
}
let n = unsafe { &*n };
if n.key == key {
let old_valptr = n.val.swap(valptr, Ordering::AcqRel);
if old_valptr.is_null() {
return None;
} else {
let old_val = unsafe { ptr::read(old_valptr) };
return Some(old_val);
}
}
m = &n.sub[(h >> 62) as usize];
h <<= 2;
}
}
/// Check if the given key exists in the hash-trie.
pub fn contains(&self, key: K) -> bool {
let mut h = {
let mut h = FNV1a::new();
key.hash(&mut h);
h.finish()
};
let mut m = &self.root;
loop {
let n = m.load(Ordering::Acquire);
if n.is_null() {
return false;
}
let n = unsafe { &*n };
if n.key == key {
return !n.val.load(Ordering::Acquire).is_null();
}
m = &n.sub[(h >> 62) as usize];
h <<= 2;
}
}
}
#[cfg(test)]
mod tests {
use crate::arena::{
GlobalArena,
LocalArena,
};
use crate::hashtrie::HTrie;
#[test]
fn test_htrie_insert() {
let ga = GlobalArena::new(128);
let la = LocalArena::new(&ga);
let ht = HTrie::new();
assert_eq!(ht.insert("foo", "bar", &la), None);
assert_eq!(ht.insert("hello", "sailor", &la), None);
assert_eq!(ht.insert("thomas", "voss", &la), None);
}
#[test]
fn test_htrie_overwrite() {
let ga = GlobalArena::new(128);
let la = LocalArena::new(&ga);
let ht = HTrie::new();
ht.insert("foo", "bar", &la);
ht.insert("hello", "sailor", &la);
ht.insert("thomas", "voss", &la);
assert_eq!(ht.insert("foo", "bar-0", &la), Some("bar"));
assert_eq!(ht.insert("hello", "sailor-0", &la), Some("sailor"));
assert_eq!(ht.insert("thomas", "voss-0", &la), Some("voss"));
assert_eq!(ht.insert("foo", "bar-1", &la), Some("bar-0"));
assert_eq!(ht.insert("hello", "sailor-1", &la), Some("sailor-0"));
assert_eq!(ht.insert("thomas", "voss-1", &la), Some("voss-0"));
}
#[test]
fn test_htrie_contains() {
let ga = GlobalArena::new(128);
let la = LocalArena::new(&ga);
let ht = HTrie::new();
assert!(!ht.contains("foo"));
assert!(!ht.contains("hello"));
assert!(!ht.contains("thomas"));
ht.insert("foo", "bar", &la);
ht.insert("hello", "sailor", &la);
ht.insert("thomas", "voss", &la);
assert!(ht.contains("foo"));
assert!(ht.contains("hello"));
assert!(ht.contains("thomas"));
}
}
|
