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
Getcall Loaderinterface that may be used to load/lazily initialize missing cache items- Thread safety
- Event handlers (insertion, update, and eviction)
- Metrics
Installation
go get github.com/jellydator/ttlcache/v3
Status
The ttlcache package is stable and used by Jellydator,
as well as thousands of other projects and organizations in production.
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, update and eviction events, cache.OnInsertion(), cache.OnUpdate() 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.OnUpdate(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 shows how to limit
memory usage for cached entries to ~5KiB.
import (
"github.com/jellydator/ttlcache"
)
func main() {
cache := ttlcache.New[string, string](
ttlcache.WithMaxCost[string, string](5120, func(item ttlcache.CostItem[string, string]) uint64 {
// Note: The below line doesn't include memory used by internal
// structures or string metadata for the key and the value.
return len(item.Key) + len(item.Value)
}),
)
cache.Set("first", "value1", ttlcache.DefaultTTL)
}
Examples & Tutorials
See the example
directory for applications demonstrating how to use ttlcache.
If you want to learn and follow along as these example applications are
built, check out the tutorials below: