go-pkgz / expirable-cache

Expirable Go LRC\LRU cache without goroutines

expirable-cache

Package cache implements expirable cache.

• Support LRC, LRU and TTL-based eviction.
• Package is thread-safe and doesn't spawn any goroutines.
• On every Set() call, cache deletes single oldest entry in case it's expired.
• In case MaxSize is set, cache deletes the oldest entry disregarding its expiration date to maintain the size, either using LRC or LRU eviction.
• In case of default TTL (10 years) and default MaxSize (0, unlimited) the cache will be truly unlimited and will never delete entries from itself automatically.

Important: only reliable way of not having expired entries stuck in a cache is to run cache.DeleteExpired periodically using time.Ticker, advisable period is 1/2 of TTL.

This cache is heavily inspired by hashicorp/golang-lru simplelru implementation. v3 implements simplelru.LRUCache interface, so if you use a subset of functions, so you can switch from github.com/hashicorp/golang-lru/v2/simplelru or github.com/hashicorp/golang-lru/v2/expirable without any changes in your code except for cache creation. Key differences are:

• Support LRC (Least Recently Created) in addition to LRU and TTL-based eviction
• Supports per-key TTL setting
• Doesn't spawn any goroutines, whereas hashicorp/golang-lru/v2/expirable spawns goroutine which is never killed (as of now)
• Provides stats about hits and misses, added and evicted entries

Usage example

package main

import (
	"fmt"
	"time"

	"github.com/go-pkgz/expirable-cache/v3"
)

func main() {
	// make cache with short TTL and 3 max keys
	c := cache.NewCache[string, string]().WithMaxKeys(3).WithTTL(time.Millisecond * 10)

	// set value under key1.
	// with 0 ttl (last parameter) will use cache-wide setting instead (10ms).
	c.Set("key1", "val1", 0)

	// get value under key1
	r, ok := c.Get("key1")

	// check for OK value, because otherwise return would be nil and
	// type conversion will panic
	if ok {
		rstr := r.(string) // convert cached value from interface{} to real type
		fmt.Printf("value before expiration is found: %v, value: %v\n", ok, rstr)
	}

	time.Sleep(time.Millisecond * 11)

	// get value under key1 after key expiration
	r, ok = c.Get("key1")
	// don't convert to string as with ok == false value would be nil
	fmt.Printf("value after expiration is found: %v, value: %v\n", ok, r)

	// set value under key2, would evict old entry because it is already expired.
	// ttl (last parameter) overrides cache-wide ttl.
	c.Set("key2", "val2", time.Minute*5)

	fmt.Printf("%+v\n", c)
	// Output:
	// value before expiration is found: true, value: val1
	// value after expiration is found: false, value: <nil>
	// Size: 1, Stats: {Hits:1 Misses:1 Added:2 Evicted:1} (50.0%)
}