cache

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 Go to latest Published: Jan 27, 2016 License: MIT Imports: 11 Imported by: 0

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 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/patrickmn/go-cache

Documentation

Index

Constants

View Source 
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
)

Variables

This section is empty.

Functions

This section is empty.

Types

type Cache 

type Cache struct {
	// contains filtered or unexported fields
}

func New 

func New(defaultExpiration, cleanupInterval time.Duration) *Cache

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

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 interface{}, 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) Decrement 

func (c Cache) Decrement(k string, n int64) error

Decrement an item of type int, int8, int16, int32, int64, uintptr, uint, uint8, uint32, or uint64, float32 or float64 by n. Returns an error if the item's value is not an integer, if it was not found, or if it is not possible to decrement it by n. To retrieve the decremented value, use one of the specialized methods, e.g. DecrementInt64.

func (Cache) DecrementFloat 

func (c Cache) DecrementFloat(k string, n float64) error

Decrement an item of type float32 or float64 by n. Returns an error if the item's value is not floating point, if it was not found, or if it is not possible to decrement it by n. Pass a negative number to decrement the value. To retrieve the decremented value, use one of the specialized methods, e.g. DecrementFloat64.

func (Cache) DecrementFloat32 

func (c Cache) DecrementFloat32(k string, n float32) (float32, error)

Decrement an item of type float32 by n. Returns an error if the item's value is not an float32, or if it was not found. If there is no error, the decremented value is returned.

func (Cache) DecrementFloat64 

func (c Cache) DecrementFloat64(k string, n float64) (float64, error)

Decrement an item of type float64 by n. Returns an error if the item's value is not an float64, or if it was not found. If there is no error, the decremented value is returned.

func (Cache) DecrementInt 

func (c Cache) DecrementInt(k string, n int) (int, error)

Decrement an item of type int by n. Returns an error if the item's value is not an int, or if it was not found. If there is no error, the decremented value is returned.

func (Cache) DecrementInt16 

func (c Cache) DecrementInt16(k string, n int16) (int16, error)

Decrement an item of type int16 by n. Returns an error if the item's value is not an int16, or if it was not found. If there is no error, the decremented value is returned.

func (Cache) DecrementInt32 

func (c Cache) DecrementInt32(k string, n int32) (int32, error)

Decrement an item of type int32 by n. Returns an error if the item's value is not an int32, or if it was not found. If there is no error, the decremented value is returned.

func (Cache) DecrementInt64 

func (c Cache) DecrementInt64(k string, n int64) (int64, error)

Decrement an item of type int64 by n. Returns an error if the item's value is not an int64, or if it was not found. If there is no error, the decremented value is returned.

func (Cache) DecrementInt8 

func (c Cache) DecrementInt8(k string, n int8) (int8, error)

Decrement an item of type int8 by n. Returns an error if the item's value is not an int8, or if it was not found. If there is no error, the decremented value is returned.

func (Cache) DecrementUint 

func (c Cache) DecrementUint(k string, n uint) (uint, error)

Decrement an item of type uint by n. Returns an error if the item's value is not an uint, or if it was not found. If there is no error, the decremented value is returned.

func (Cache) DecrementUint16 

func (c Cache) DecrementUint16(k string, n uint16) (uint16, error)

Decrement an item of type uint16 by n. Returns an error if the item's value is not an uint16, or if it was not found. If there is no error, the decremented value is returned.

func (Cache) DecrementUint32 

func (c Cache) DecrementUint32(k string, n uint32) (uint32, error)

Decrement an item of type uint32 by n. Returns an error if the item's value is not an uint32, or if it was not found. If there is no error, the decremented value is returned.

func (Cache) DecrementUint64 

func (c Cache) DecrementUint64(k string, n uint64) (uint64, error)

Decrement an item of type uint64 by n. Returns an error if the item's value is not an uint64, or if it was not found. If there is no error, the decremented value is returned.

func (Cache) DecrementUint8 

func (c Cache) DecrementUint8(k string, n uint8) (uint8, error)

Decrement an item of type uint8 by n. Returns an error if the item's value is not an uint8, or if it was not found. If there is no error, the decremented value is returned.

func (Cache) DecrementUintptr 

func (c Cache) DecrementUintptr(k string, n uintptr) (uintptr, error)

Decrement an item of type uintptr by n. Returns an error if the item's value is not an uintptr, or if it was not found. If there is no error, the decremented value is returned.

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) (interface{}, bool)

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

func (Cache) Increment 

func (c Cache) Increment(k string, n int64) error

Increment an item of type int, int8, int16, int32, int64, uintptr, uint, uint8, uint32, or uint64, float32 or float64 by n. Returns an error if the item's value is not an integer, if it was not found, or if it is not possible to increment it by n. To retrieve the incremented value, use one of the specialized methods, e.g. IncrementInt64.

func (Cache) IncrementFloat 

func (c Cache) IncrementFloat(k string, n float64) error

Increment an item of type float32 or float64 by n. Returns an error if the item's value is not floating point, if it was not found, or if it is not possible to increment it by n. Pass a negative number to decrement the value. To retrieve the incremented value, use one of the specialized methods, e.g. IncrementFloat64.

func (Cache) IncrementFloat32 

func (c Cache) IncrementFloat32(k string, n float32) (float32, error)

Increment an item of type float32 by n. Returns an error if the item's value is not an float32, or if it was not found. If there is no error, the incremented value is returned.

func (Cache) IncrementFloat64 

func (c Cache) IncrementFloat64(k string, n float64) (float64, error)

Increment an item of type float64 by n. Returns an error if the item's value is not an float64, or if it was not found. If there is no error, the incremented value is returned.

func (Cache) IncrementInt 

func (c Cache) IncrementInt(k string, n int) (int, error)

Increment an item of type int by n. Returns an error if the item's value is not an int, or if it was not found. If there is no error, the incremented value is returned.

func (Cache) IncrementInt16 

func (c Cache) IncrementInt16(k string, n int16) (int16, error)

Increment an item of type int16 by n. Returns an error if the item's value is not an int16, or if it was not found. If there is no error, the incremented value is returned.

func (Cache) IncrementInt32 

func (c Cache) IncrementInt32(k string, n int32) (int32, error)

Increment an item of type int32 by n. Returns an error if the item's value is not an int32, or if it was not found. If there is no error, the incremented value is returned.

func (Cache) IncrementInt64 

func (c Cache) IncrementInt64(k string, n int64) (int64, error)

Increment an item of type int64 by n. Returns an error if the item's value is not an int64, or if it was not found. If there is no error, the incremented value is returned.

func (Cache) IncrementInt8 

func (c Cache) IncrementInt8(k string, n int8) (int8, error)

Increment an item of type int8 by n. Returns an error if the item's value is not an int8, or if it was not found. If there is no error, the incremented value is returned.

func (Cache) IncrementUint 

func (c Cache) IncrementUint(k string, n uint) (uint, error)

Increment an item of type uint by n. Returns an error if the item's value is not an uint, or if it was not found. If there is no error, the incremented value is returned.

func (Cache) IncrementUint16 

func (c Cache) IncrementUint16(k string, n uint16) (uint16, error)

Increment an item of type uint16 by n. Returns an error if the item's value is not an uint16, or if it was not found. If there is no error, the incremented value is returned.

func (Cache) IncrementUint32 

func (c Cache) IncrementUint32(k string, n uint32) (uint32, error)

Increment an item of type uint32 by n. Returns an error if the item's value is not an uint32, or if it was not found. If there is no error, the incremented value is returned.

func (Cache) IncrementUint64 

func (c Cache) IncrementUint64(k string, n uint64) (uint64, error)

Increment an item of type uint64 by n. Returns an error if the item's value is not an uint64, or if it was not found. If there is no error, the incremented value is returned.

func (Cache) IncrementUint8 

func (c Cache) IncrementUint8(k string, n uint8) (uint8, error)

Increment an item of type uint8 by n. Returns an error if the item's value is not an uint8, or if it was not found. If there is no error, the incremented value is returned.

func (Cache) IncrementUintptr 

func (c Cache) IncrementUintptr(k string, n uintptr) (uintptr, error)

Increment an item of type uintptr by n. Returns an error if the item's value is not an uintptr, or if it was not found. If there is no error, the incremented value is returned.

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. Equivalent to len(c.Items()).

func (Cache) Items 

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

Returns the items in the cache. This may include items that have expired, but have not yet been cleaned up. If this is significant, the Expiration fields of the items should be checked. Note that explicit synchronization is needed to use a cache and its corresponding Items() return value at the same time, as the map is shared.

func (Cache) Load 

func (c Cache) Load(r io.Reader) error

Add (Gob-serialized) cache items from an io.Reader, excluding any items with keys that already exist (and haven't expired) in the current cache.

NOTE: This method is deprecated in favor of c.Items() and NewFrom() (see the documentation for NewFrom().)

func (Cache) LoadFile 

func (c Cache) LoadFile(fname string) error

Load and add cache items from the given filename, excluding any items with keys that already exist in the current cache.

NOTE: This method is deprecated in favor of c.Items() and NewFrom() (see the documentation for NewFrom().)

func (Cache) OnEvicted 

func (c Cache) OnEvicted(f func(string, interface{}))

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 interface{}, 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) Save 

func (c Cache) Save(w io.Writer) (err error)

Write the cache's items (using Gob) to an io.Writer.

NOTE: This method is deprecated in favor of c.Items() and NewFrom() (see the documentation for NewFrom().)

func (Cache) SaveFile 

func (c Cache) SaveFile(fname string) error

Save the cache's items to the given filename, creating the file if it doesn't exist, and overwriting it if it does.

NOTE: This method is deprecated in favor of c.Items() and NewFrom() (see the documentation for NewFrom().)

func (Cache) Set 

func (c Cache) Set(k string, x interface{}, 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.

type Item 

type Item struct {
	Object     interface{}
	Expiration int64
}

func (Item) Expired 

func (item Item) Expired() bool

Returns true if the item has expired.

Source Files

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