TTLCache - an in-memory cache with item expiration and generics

Features

• Simple API
• Type parameters
• Item expiration and automatic deletion
• Automatic expiration time extension on each Get call
• Loader interface that may be used to load/lazily initialize missing cache
• Thread Safe items
• Event handlers (insertion and eviction)
• Metrics

Installation

go get github.com/jellydator/ttlcache/v3

Usage

The main type of ttlcache is Cache. It represents a single in-memory data store.

To create a new instance of ttlcache.Cache, the ttlcache.New() function should be called:

func main() {
	cache := ttlcache.New[string, string]()
}

Note that by default, a new cache instance does not let any of its items to expire or be automatically deleted. However, this feature can be activated by passing a few additional options into the ttlcache.New() function and calling the cache.Start() method:

func main() {
	cache := ttlcache.New[string, string](
		ttlcache.WithTTL[string, string](30 * time.Minute),
	)

	go cache.Start() // starts automatic expired item deletion
}

Even though the cache.Start() method handles expired item deletion well, there may be times when the system that uses ttlcache needs to determine when to delete the expired items itself. For example, it may need to delete them only when the resource load is at its lowest (e.g., after midnight, when the number of users/HTTP requests drops). So, in situations like these, instead of calling cache.Start(), the system could periodically call cache.DeleteExpired():

func main() {
	cache := ttlcache.New[string, string](
		ttlcache.WithTTL[string, string](30 * time.Minute),
	)

	for {
		time.Sleep(4 * time.Hour)
		cache.DeleteExpired()
	}
}

The data stored in ttlcache.Cache can be retrieved, checked and updated with Set, Get, Delete, Has etc. methods:

func main() {
	cache := ttlcache.New[string, string](
		ttlcache.WithTTL[string, string](30 * time.Minute),
	)

	// insert data
	cache.Set("first", "value1", ttlcache.DefaultTTL)
	cache.Set("second", "value2", ttlcache.NoTTL)
	cache.Set("third", "value3", ttlcache.DefaultTTL)

	// retrieve data
	item := cache.Get("first")
	fmt.Println(item.Value(), item.ExpiresAt())

	// check key 
	ok := cache.Has("third")
	
	// delete data
	cache.Delete("second")
	cache.DeleteExpired()
	cache.DeleteAll()

	// retrieve data if in cache otherwise insert data
	item, retrieved := cache.GetOrSet("fourth", "value4", WithTTL[string, string](ttlcache.DefaultTTL))

	// retrieve and delete data
	item, present := cache.GetAndDelete("fourth")
}

To subscribe to insertion and eviction events, cache.OnInsertion() and cache.OnEviction() methods should be used:

func main() {
	cache := ttlcache.New[string, string](
		ttlcache.WithTTL[string, string](30 * time.Minute),
		ttlcache.WithCapacity[string, string](300),
	)

	cache.OnInsertion(func(ctx context.Context, item *ttlcache.Item[string, string]) {
		fmt.Println(item.Value(), item.ExpiresAt())
	})
	cache.OnEviction(func(ctx context.Context, reason ttlcache.EvictionReason, item *ttlcache.Item[string, string]) {
		if reason == ttlcache.EvictionReasonCapacityReached {
			fmt.Println(item.Key(), item.Value())
		}
	})

	cache.Set("first", "value1", ttlcache.DefaultTTL)
	cache.DeleteAll()
}

To load data when the cache does not have it, a custom or existing implementation of ttlcache.Loader can be used:

func main() {
	loader := ttlcache.LoaderFunc[string, string](
		func(c *ttlcache.Cache[string, string], key string) *ttlcache.Item[string, string] {
			// load from file/make an HTTP request
			item := c.Set("key from file", "value from file")
			return item
		},
	)
	cache := ttlcache.New[string, string](
		ttlcache.WithLoader[string, string](loader),
	)

	item := cache.Get("key from file")
}

To restrict the cache's capacity based on criteria beyond the number of items it can hold, the ttlcache.WithMaxCost option allows for implementing custom strategies. The following example demonstrates how to limit the maximum memory usage of a cache to 5KiB:

import (
    "github.com/jellydator/ttlcache"
    "github.com/DmitriyVTitov/size"
)

func main() {
    cache := ttlcache.New[string, string](
        ttlcache.WithMaxCost[string, string](5120, func(item *ttlcache.Item[string, string]) uint64 {
            return uint64(size.Of(item))
        }), 
    )

    cache.Set("first", "value1", ttlcache.DefaultTTL)
}