go-cache

go-cache is an in-memory key:value store/cache similar to memcached that is suitable for applications running on a single machine. Its major advantage is that, being essentially a thread-safe map[string]interface{} with expiration times, it doesn't need to serialize or transmit its contents over the network.

Any object can be stored, for a given duration or forever, and the cache can be safely used by multiple goroutines.

Although go-cache isn't meant to be used as a persistent datastore, the entire cache can be saved to and loaded from a file (using c.Items() to retrieve the items map to serialize, and NewFrom() to create a cache from a deserialized one) to recover from downtime quickly. (See the docs for NewFrom() for caveats.)

When creating a cache object using NewWithLRU(), if you set the maxItems value above 0, the LRU functionality is enabled. The cache automatically updates a timestamp every time a given item is retrieved. In the background, the janitor takes care of deleting items that have expired because of staleness, or are least-recently-used when the cache is under pressure. Whatever you set your purge interval to controls when the item will actually be removed from the cache. If you don't want to use the janitor, and wish to manually purge LRU items, then c.DeleteLRU(n) where n is the number of items you'd like to purge.

Installation

go get github.com/pmylund/go-cache

Usage

import (
	"fmt"
	"github.com/pmylund/go-cache"
)

func main() {

	// Create a cache with a default expiration time of 5 minutes, and which
	// purges expired items every 30 seconds
	c := cache.New(5*time.Minute, 30*time.Second)

	// Set the value of the key "foo" to "bar", with the default expiration time
	c.Set("foo", "bar", cache.DefaultExpiration)

	// Set the value of the key "baz" to 42, with no expiration time
	// (the item won't be removed until it is re-set, or removed using
	// c.Delete("baz")
	c.Set("baz", 42, cache.NoExpiration)

	// Get the string associated with the key "foo" from the cache
	foo, found := c.Get("foo")
	if found {
		fmt.Println(foo)
	}

	// Since Go is statically typed, and cache values can be anything, type
	// assertion is needed when values are being passed to functions that don't
	// take arbitrary types, (i.e. interface{}). The simplest way to do this for
	// values which will only be used once--e.g. for passing to another
	// function--is:
	foo, found := c.Get("foo")
	if found {
		MyFunction(foo.(string))
	}

	// This gets tedious if the value is used several times in the same function.
	// You might do either of the following instead:
	if x, found := c.Get("foo"); found {
		foo := x.(string)
		// ...
	}
	// or
	var foo string
	if x, found := c.Get("foo"); found {
		foo = x.(string)
	}
	// ...
	// foo can then be passed around freely as a string

	// Want performance? Store pointers!
	c.Set("foo", &MyStruct, cache.DefaultExpiration)
	if x, found := c.Get("foo"); found {
		foo := x.(*MyStruct)
		// ...
	}

	// If you store a reference type like a pointer, slice, map or channel, you
	// do not need to run Set if you modify the underlying data. The cached
	// reference points to the same memory, so if you modify a struct whose
	// pointer you've stored in the cache, retrieving that pointer with Get will
	// point you to the same data:
	foo := &MyStruct{Num: 1}
	c.Set("foo", foo, cache.DefaultExpiration)
	// ...
	x, _ := c.Get("foo")
	foo := x.(*MyStruct)
	fmt.Println(foo.Num)
	// ...
	foo.Num++
	// ...
	x, _ := c.Get("foo")
	foo := x.(*MyStruct)
	foo.Println(foo.Num)

	// will print:
	// 1
	// 2

}

Reference

godoc or http://godoc.org/github.com/pmylund/go-cache