cache

README

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.)

Installation

go get github.com/patrickmn/go-cache

Usage

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

func main() {
	// Create a cache with a default expiration time of 5 minutes, and which
	// purges expired items every 10 minutes
	c := cache.New(5*time.Minute, 10*time.Minute)

	// 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)
			// ...
	}
}

Reference

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

Documentation

Index

• Constants
• type Cache
  • func New[V any](defaultExpiration, cleanupInterval time.Duration) *Cache[V]
  • func NewFrom[V any](defaultExpiration, cleanupInterval time.Duration, items map[string]Item[V]) *Cache[V]
  • func (c Cache) Add(k string, x V, d time.Duration) error
  • func (c Cache) Delete(k string)
  • func (c Cache) DeleteExpired()
  • func (c Cache) Flush()
  • func (c Cache) Get(k string) (V, bool)
  • func (c Cache) GetWithExpiration(k string) (V, time.Time, bool)
  • func (c Cache) ItemCount() int
  • func (c Cache) Items() map[string]Item[V]
  • func (c Cache) OnEvicted(f func(string, V))
  • func (c Cache) Replace(k string, x V, d time.Duration) error
  • func (c Cache) Set(k string, x V, d time.Duration)
  • func (c Cache) SetDefault(k string, x V)
• type Item
  • func (item Item[V]) Expired() bool
• type Number
• type NumberCache
  • func NewNumberCache[T Number](defaultExpiration, cleanupInterval time.Duration) *NumberCache[T]
  • func (c NumberCache) Add(k string, x V, d time.Duration) error
  • func (c *NumberCache[T]) Decrement(k string, n T) (T, error)
  • func (c NumberCache) Delete(k string)
  • func (c NumberCache) DeleteExpired()
  • func (c NumberCache) Flush()
  • func (c NumberCache) Get(k string) (V, bool)
  • func (c NumberCache) GetWithExpiration(k string) (V, time.Time, bool)
  • func (c *NumberCache[T]) Increment(k string, n T) (T, error)
  • func (c NumberCache) ItemCount() int
  • func (c NumberCache) Items() map[string]Item[V]
  • func (c NumberCache) OnEvicted(f func(string, V))
  • func (c NumberCache) Replace(k string, x V, d time.Duration) error
  • func (c NumberCache) Set(k string, x V, d time.Duration)
  • func (c NumberCache) SetDefault(k string, x V)

Constants

const (
	// For use with functions that take an expiration time.
	NoExpiration time.Duration = -1
	// For use with functions that take an expiration time. Equivalent to
	// passing in the same expiration duration as was given to New() or
	// NewFrom() when the cache was created (e.g. 5 minutes.)
	DefaultExpiration time.Duration = 0
)

Types

type Cache

type Cache[V any] struct {
	// contains filtered or unexported fields
}

func New

func New[V any](defaultExpiration, cleanupInterval time.Duration) *Cache[V]

Return a new cache with a given default expiration duration and cleanup interval. If the expiration duration is less than one (or NoExpiration), the items in the cache never expire (by default), and must be deleted manually. If the cleanup interval is less than one, expired items are not deleted from the cache before calling c.DeleteExpired().

func NewFrom

func NewFrom[V any](defaultExpiration, cleanupInterval time.Duration, items map[string]Item[V]) *Cache[V]

Return a new cache with a given default expiration duration and cleanup interval. If the expiration duration is less than one (or NoExpiration), the items in the cache never expire (by default), and must be deleted manually. If the cleanup interval is less than one, expired items are not deleted from the cache before calling c.DeleteExpired().

NewFrom() also accepts an items map which will serve as the underlying map for the cache. This is useful for starting from a deserialized cache (serialized using e.g. gob.Encode() on c.Items()), or passing in e.g. make(map[string]Item, 500) to improve startup performance when the cache is expected to reach a certain minimum size.

Only the cache's methods synchronize access to this map, so it is not recommended to keep any references to the map around after creating a cache. If need be, the map can be accessed at a later point using c.Items() (subject to the same caveat.)

Note regarding serialization: When using e.g. gob, make sure to gob.Register() the individual types stored in the cache before encoding a map retrieved with c.Items(), and to register those same types before decoding a blob containing an items map.

func (Cache) Add

func (c Cache) Add(k string, x V, d time.Duration) error

Add an item to the cache only if an item doesn't already exist for the given key, or if the existing item has expired. Returns an error otherwise.

func (Cache) Delete

func (c Cache) Delete(k string)

Delete an item from the cache. Does nothing if the key is not in the cache.

func (Cache) DeleteExpired

func (c Cache) DeleteExpired()

Delete all expired items from the cache.

func (Cache) Flush

func (c Cache) Flush()

Delete all items from the cache.

func (Cache) Get

func (c Cache) Get(k string) (V, bool)

Get an item from the cache. Returns the item or nil, and a bool indicating whether the key was found.

func (Cache) GetWithExpiration

func (c Cache) GetWithExpiration(k string) (V, time.Time, bool)

GetWithExpiration returns an item and its expiration time from the cache. It returns the item or nil, the expiration time if one is set (if the item never expires a zero value for time.Time is returned), and a bool indicating whether the key was found.

func (Cache) ItemCount

func (c Cache) ItemCount() int

Returns the number of items in the cache. This may include items that have expired, but have not yet been cleaned up.

func (Cache) Items

func (c Cache) Items() map[string]Item[V]

Copies all unexpired items in the cache into a new map and returns it.

func (Cache) OnEvicted

func (c Cache) OnEvicted(f func(string, V))

Sets an (optional) function that is called with the key and value when an item is evicted from the cache. (Including when it is deleted manually, but not when it is overwritten.) Set to nil to disable.

func (Cache) Replace

func (c Cache) Replace(k string, x V, d time.Duration) error

Set a new value for the cache key only if it already exists, and the existing item hasn't expired. Returns an error otherwise.

func (Cache) Set

func (c Cache) Set(k string, x V, d time.Duration)

Add an item to the cache, replacing any existing item. If the duration is 0 (DefaultExpiration), the cache's default expiration time is used. If it is -1 (NoExpiration), the item never expires.

func (Cache) SetDefault

func (c Cache) SetDefault(k string, x V)

Add an item to the cache, replacing any existing item, using the default expiration.

type Item

type Item[V any] struct {
	Object     V
	Expiration int64
}

func (Item[V]) Expired

func (item Item[V]) Expired() bool

Returns true if the item has expired.

type Number

type Number interface {
	~int | ~int8 | ~int16 | ~int32 | ~int64 | ~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~float32 | ~float64
}

type NumberCache

type NumberCache[T Number] struct {
	// contains filtered or unexported fields
}

func NewNumberCache

func NewNumberCache[T Number](defaultExpiration, cleanupInterval time.Duration) *NumberCache[T]

func (NumberCache) Add

func (c NumberCache) Add(k string, x V, d time.Duration) error

Add an item to the cache only if an item doesn't already exist for the given key, or if the existing item has expired. Returns an error otherwise.

func (*NumberCache[T]) Decrement

func (c *NumberCache[T]) Decrement(k string, n T) (T, error)

func (NumberCache) Delete

func (c NumberCache) Delete(k string)

Delete an item from the cache. Does nothing if the key is not in the cache.

func (NumberCache) DeleteExpired

func (c NumberCache) DeleteExpired()

Delete all expired items from the cache.

func (NumberCache) Flush

func (c NumberCache) Flush()

Delete all items from the cache.

func (NumberCache) Get

func (c NumberCache) Get(k string) (V, bool)

Get an item from the cache. Returns the item or nil, and a bool indicating whether the key was found.

func (NumberCache) GetWithExpiration

func (c NumberCache) GetWithExpiration(k string) (V, time.Time, bool)

GetWithExpiration returns an item and its expiration time from the cache. It returns the item or nil, the expiration time if one is set (if the item never expires a zero value for time.Time is returned), and a bool indicating whether the key was found.

func (*NumberCache[T]) Increment

func (c *NumberCache[T]) Increment(k string, n T) (T, error)

func (NumberCache) ItemCount

func (c NumberCache) ItemCount() int

Returns the number of items in the cache. This may include items that have expired, but have not yet been cleaned up.

func (NumberCache) Items

func (c NumberCache) Items() map[string]Item[V]

Copies all unexpired items in the cache into a new map and returns it.

func (NumberCache) OnEvicted

func (c NumberCache) OnEvicted(f func(string, V))

Sets an (optional) function that is called with the key and value when an item is evicted from the cache. (Including when it is deleted manually, but not when it is overwritten.) Set to nil to disable.

func (NumberCache) Replace

func (c NumberCache) Replace(k string, x V, d time.Duration) error

Set a new value for the cache key only if it already exists, and the existing item hasn't expired. Returns an error otherwise.

func (NumberCache) Set

func (c NumberCache) Set(k string, x V, d time.Duration)

Add an item to the cache, replacing any existing item. If the duration is 0 (DefaultExpiration), the cache's default expiration time is used. If it is -1 (NoExpiration), the item never expires.

func (NumberCache) SetDefault

func (c NumberCache) SetDefault(k string, x V)

Add an item to the cache, replacing any existing item, using the default expiration.