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//! LRU cache for frequently accessed graph query results
//!
//! Provides LRU caching for file nodes and symbol lookups
//! to reduce database round-trips for hot data.
//!
//! # Thread Safety
//!
//! **This cache is NOT thread-safe.**
//!
//! `LruCache<K, V>` and `FileNodeCache` are designed for single-threaded use:
//! - All methods require `&mut self` (exclusive mutable access)
//! - `HashMap` and `VecDeque` have no synchronization primitives
//! - No `Send` or `Sync` impls
//!
//! # Usage Pattern
//!
//! `FileNodeCache` is accessed exclusively through `CodeGraph`, which
//! enforces single-threaded access. Do not share the cache directly
//! across threads.
//!
//! For concurrent caching, wrap in `Mutex<LruCache<...>>` or use
//! a thread-safe cache library (e.g., `moka`).
use std::collections::{HashMap, VecDeque};
use std::hash::Hash;
/// Cache statistics for monitoring effectiveness
#[derive(Debug, Clone, Default)]
pub struct CacheStats {
pub hits: usize,
pub misses: usize,
pub size: usize,
}
impl CacheStats {
/// Calculate cache hit rate as a percentage (0.0 to 1.0)
pub fn hit_rate(&self) -> f64 {
let total = self.hits + self.misses;
if total == 0 {
0.0
} else {
self.hits as f64 / total as f64
}
}
}
/// Simple LRU cache implementation
///
/// Uses HashMap for O(1) lookups and VecDeque for tracking access order.
/// When capacity is reached, the least recently used item is evicted.
pub struct LruCache<K, V> {
capacity: usize,
map: HashMap<K, V>,
order: VecDeque<K>,
hits: usize,
misses: usize,
}
impl<K: Hash + Eq + Clone, V> LruCache<K, V> {
/// Create a new LRU cache with the specified capacity
pub fn new(capacity: usize) -> Self {
Self {
capacity,
map: HashMap::new(),
order: VecDeque::with_capacity(capacity),
hits: 0,
misses: 0,
}
}
/// Get a value from the cache by key
///
/// Returns a reference to the value if present, None otherwise.
/// On cache hit, the item is moved to the front of the LRU order.
pub fn get(&mut self, key: &K) -> Option<&V> {
if self.map.contains_key(key) {
self.hits += 1;
// Move to front of order
if let Some(pos) = self.order.iter().position(|k| k == key) {
self.order.remove(pos);
self.order.push_front(key.clone());
}
self.map.get(key)
} else {
self.misses += 1;
None
}
}
/// Insert a key-value pair into the cache
///
/// If the key already exists, the value is updated and the key is moved to front.
/// If the cache is at capacity, the least recently used item is evicted.
pub fn put(&mut self, key: K, value: V) {
if self.map.contains_key(&key) {
// Update existing: remove from current position
if let Some(pos) = self.order.iter().position(|k| k == &key) {
self.order.remove(pos);
}
} else if self.order.len() >= self.capacity {
// Evict oldest (least recently used)
if let Some(old) = self.order.pop_back() {
self.map.remove(&old);
}
}
// Clone key for both order tracking and map insertion
let key_clone = key.clone();
self.order.push_front(key_clone);
self.map.insert(key, value);
}
/// Invalidate a specific cache entry
///
/// Removes the key and its value from the cache if present.
pub fn invalidate(&mut self, key: &K) {
self.map.remove(key);
if let Some(pos) = self.order.iter().position(|k| k == key) {
self.order.remove(pos);
}
}
/// Clear all entries from the cache
pub fn clear(&mut self) {
self.map.clear();
self.order.clear();
self.hits = 0;
self.misses = 0;
}
/// Get current cache size
///
/// Provided for API completeness and debugging. Currently unused internally
/// but kept for public API surface.
#[allow(dead_code)] // Provided for API completeness and debugging
pub fn len(&self) -> usize {
self.map.len()
}
/// Check if cache is empty
///
/// Provided for API completeness and debugging. Currently unused internally
/// but kept for public API surface.
#[allow(dead_code)] // Provided for API completeness and debugging
pub fn is_empty(&self) -> bool {
self.map.is_empty()
}
/// Get cache statistics
pub fn stats(&self) -> CacheStats {
CacheStats {
hits: self.hits,
misses: self.misses,
size: self.map.len(),
}
}
/// Get hit rate as a percentage (0.0 to 1.0)
///
/// Provided for API completeness and debugging. Currently unused internally
/// but kept for public API surface.
#[allow(dead_code)] // Provided for API completeness and debugging
pub fn hit_rate(&self) -> f64 {
self.stats().hit_rate()
}
}
/// Specialized cache for file nodes
///
/// Caches FileNode lookups by file path to avoid repeated database queries.
pub type FileNodeCache = LruCache<String, crate::graph::schema::FileNode>;
/// Specialized cache for symbol vectors
///
/// Caches symbol vectors by file path for faster symbol lookups.
/// Currently unused internally but provided for API completeness and future use.
#[expect(dead_code)] // Future use: symbol vector caching
pub type SymbolCache = LruCache<String, Vec<crate::ingest::SymbolFact>>;
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_lru_cache_basic_operations() {
let mut cache: LruCache<String, i32> = LruCache::new(3);
// Empty cache
assert_eq!(cache.get(&"a".to_string()), None);
assert_eq!(cache.len(), 0);
assert!(cache.is_empty());
// Insert and get
cache.put("a".to_string(), 1);
cache.put("b".to_string(), 2);
assert_eq!(cache.get(&"a".to_string()), Some(&1));
assert_eq!(cache.get(&"b".to_string()), Some(&2));
assert_eq!(cache.len(), 2);
assert!(!cache.is_empty());
}
#[test]
fn test_lru_cache_eviction() {
let mut cache: LruCache<String, i32> = LruCache::new(2);
cache.put("a".to_string(), 1);
cache.put("b".to_string(), 2);
// Access 'a' to make it more recently used than 'b'
cache.get(&"a".to_string());
// Insert 'c' - should evict 'b' (least recently used)
cache.put("c".to_string(), 3);
assert_eq!(cache.get(&"a".to_string()), Some(&1));
assert_eq!(cache.get(&"b".to_string()), None); // Evicted
assert_eq!(cache.get(&"c".to_string()), Some(&3));
assert_eq!(cache.len(), 2);
}
#[test]
fn test_lru_cache_update_existing() {
let mut cache: LruCache<String, i32> = LruCache::new(3);
cache.put("a".to_string(), 1);
cache.put("b".to_string(), 2);
cache.put("c".to_string(), 3);
// Update 'a' and verify it moves to front
cache.put("a".to_string(), 10);
// Add 'd' - should evict 'b' (now LRU since 'a' was updated)
cache.put("d".to_string(), 4);
assert_eq!(cache.get(&"a".to_string()), Some(&10));
assert_eq!(cache.get(&"b".to_string()), None); // Evicted
assert_eq!(cache.get(&"c".to_string()), Some(&3));
assert_eq!(cache.get(&"d".to_string()), Some(&4));
assert_eq!(cache.len(), 3);
}
#[test]
fn test_lru_cache_invalidate() {
let mut cache: LruCache<String, i32> = LruCache::new(3);
cache.put("a".to_string(), 1);
cache.put("b".to_string(), 2);
cache.put("c".to_string(), 3);
// Invalidate 'b'
cache.invalidate(&"b".to_string());
assert_eq!(cache.get(&"a".to_string()), Some(&1));
assert_eq!(cache.get(&"b".to_string()), None);
assert_eq!(cache.get(&"c".to_string()), Some(&3));
assert_eq!(cache.len(), 2);
}
#[test]
fn test_lru_cache_clear() {
let mut cache: LruCache<String, i32> = LruCache::new(3);
cache.put("a".to_string(), 1);
cache.put("b".to_string(), 2);
cache.clear();
assert_eq!(cache.len(), 0);
assert!(cache.is_empty());
assert_eq!(cache.get(&"a".to_string()), None);
}
#[test]
fn test_cache_stats() {
let mut cache: LruCache<String, i32> = LruCache::new(3);
cache.put("a".to_string(), 1);
cache.put("b".to_string(), 2);
// Generate some hits and misses
cache.get(&"a".to_string()); // hit
cache.get(&"b".to_string()); // hit
cache.get(&"c".to_string()); // miss
let stats = cache.stats();
assert_eq!(stats.hits, 2);
assert_eq!(stats.misses, 1);
assert_eq!(stats.size, 2);
let hit_rate = cache.hit_rate();
assert!((hit_rate - 2.0 / 3.0).abs() < f64::EPSILON);
}
#[test]
fn test_cache_hit_rate_empty() {
let cache: LruCache<String, i32> = LruCache::new(3);
assert_eq!(cache.hit_rate(), 0.0);
}
#[test]
fn test_cache_hit_rate_all_hits() {
let mut cache: LruCache<String, i32> = LruCache::new(3);
cache.put("a".to_string(), 1);
cache.get(&"a".to_string());
cache.get(&"a".to_string());
assert_eq!(cache.hit_rate(), 1.0);
}
#[test]
fn test_cache_hit_rate_all_misses() {
let mut cache: LruCache<String, i32> = LruCache::new(3);
cache.get(&"a".to_string());
cache.get(&"b".to_string());
assert_eq!(cache.hit_rate(), 0.0);
}
}