zcache

package module
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 Go to latest Published: May 26, 2022 License: MIT Imports: 4 Imported by: 5

README

zcache is an in-memory key:value store/cache with time-based evictions.

It is suitable for applications running on a single machine. Its major advantage is that it's essentially a thread-safe map with expiration times. Any object can be stored, for a given duration or forever, and the cache can be safely used by multiple goroutines.

Although zcache isn't meant to be used as a persistent datastore, the contents 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.

The canonical import path is zgo.at/zcache, and reference docs are at https://godocs.io/zgo.at/zcache

This is a fork of https://github.com/patrickmn/go-cache – which no longer seems actively maintained. There are two versions of zcache:

  • v1 is intended to be 100% compatible with co-cache and a drop-in replacement with various enhancements.
  • v2 makes various incompatible changes to the API: various functions calls are improved. This uses generics and requires Go 1.18.

This README documents v2; see README.v1.md for the v1 README. Both versions are maintained. See the "changes" section below for a list of changes.

Usage

Some examples from example_test.go:

func ExampleSimple() {
	// Create a cache with a default expiration time of 5 minutes, and which
	// purges expired items every 10 minutes.
	//
	// This creates a cache with string keys and values, with Go 1.18 type
	// parameters.
	c := zcache.New[string, string](5*time.Minute, 10*time.Minute)

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

	// Set the value of the key "baz" to "never", with no expiration time. The
	// item won't be removed until it's removed with c.Delete("baz").
	c.SetWithExpire("baz", "never", zcache.NoExpiration)

	// Get the value associated with the key "foo" from the cache; due to the
	// use of type parameters this is a string, and no type assertions are
	// needed.
	foo, ok := c.Get("foo")
	if ok {
		fmt.Println(foo)
	}

	// Output: bar
}

func ExampleStruct() {
	type MyStruct struct{ Value string }

	// Create a new cache that stores a specific struct.
	c := zcache.New[string, *MyStruct](zcache.NoExpiration, zcache.NoExpiration)
	c.Set("cache", &MyStruct{Value: "value"})

	v, _ := c.Get("cache")
	fmt.Printf("%#v\n", v)

	// Output: &zcache_test.MyStruct{Value:"value"}
}

func ExampleAny() {
	// Create a new cache that stores any value, behaving similar to zcache v1
	// or go-cache.
	c := zcache.New[string, any](zcache.NoExpiration, zcache.NoExpiration)

	c.Set("a", "value 1")
	c.Set("b", 42)

	a, _ := c.Get("a")
	b, _ := c.Get("b")

	// This needs type assertions.
	p := func(a string, b int) { fmt.Println(a, b) }
	p(a.(string), b.(int))

	// Output: value 1 42
}

func ExampleProxy() {
	type Site struct {
		ID       int
		Hostname string
	}

	site := &Site{
		ID:       42,
		Hostname: "example.com",
	}

	// Create a new site which caches by site ID (int), and a "proxy" which
	// caches by the hostname (string).
	c := zcache.New[int, *Site](zcache.NoExpiration, zcache.NoExpiration)
	p := zcache.NewProxy[string, int, *Site](c)

	p.Set(42, "example.com", site)

	siteByID, ok := c.Get(42)
	fmt.Printf("%v %v\n", ok, siteByID)

	siteByHost, ok := p.Get("example.com")
	fmt.Printf("%v %v\n", ok, siteByHost)

	// They're both the same object/pointer.
	fmt.Printf("%v\n", siteByID == siteByHost)

	// Output:
	// true &{42 example.com}
	// true &{42 example.com}
	// true
}

Changes

Incompatible changes in v2

  • Use type parameters instead of map[string]interface{}; you can get the same as before with zcache.New[string, any](..), but if you know you will only store MyStruct you can use zcache.New[string, *MyStruct](..) for additional type safety.

  • Remove Save(), SaveFile(), Load(), LoadFile(); you can still persist stuff to disk by using Items() and NewFrom(). These methods were already deprecated.

  • Rename Set() to SetWithExpire(), and rename SetDefault() to Set(). Most of the time you want to use the default expiry time, so make that the easier path.

  • The Increment* and Decrement* functions have been removed; you can replace them with Modify():

    cache := New[string, int](DefaultExpiration, 0)
cache.Set("one", 1)
cache.Modify("one", func(v int) int { return v + 1 })

    The performance of this is roughly the same as the old Increment, and this is a more generic method that can also be used for other things like appending to a slice.

  • Rename Flush() to Reset(); I think that more clearly conveys what it's intended for as Flush() is typically used to flush a buffer or the like.

Compatible changes from go-cache

All these changes are in both v1 and v2:

  • Add Keys() to list all keys.
  • Add Touch() to update the expiry on an item.
  • Add GetStale() to get items even after they've expired.
  • Add Pop() to get an item and delete it.
  • Add Modify() to atomically modify existing cache entries (e.g. lists, maps).
  • Add DeleteAll() to remove all items from the cache with onEvicted call.
  • Add DeleteFunc() to remove specific items from the cache atomically.
  • Add Rename() to rename keys, retaining the value and expiry.
  • Add Proxy type, to access cache items under a different key.
  • Various small internal and documentation improvements.

See issue-list.markdown for a complete run-down of the PRs/issues for go-cache and what was and wasn't included.

FAQ

How can I limit the size of the cache? Is there an option for this?

Not really; zcache is intended as a thread-safe map with time-based eviction. This keeps it nice and simple. Adding something like a LRU eviction mechanism not only makes the code more complex, it also makes the library worse for cases where you just want a map since it requires additional memory and makes some operations more expensive (unless a new API is added which make the API worse for those use cases).

So unless I or someone else comes up with a way to do this which doesn't detract anything from the simple map use case, I'd rather not add it. Perhaps wrapping zcache.Cache and overriding some methods could work, but I haven't looked at it.

tl;dr: this isn't designed to solve every caching use case. That's a feature.

Documentation

Overview

Package zcache is an in-memory key:value store/cache with time-based evictions.

It is suitable for applications running on a single machine. Its major advantage is that it's essentially a thread-safe map with expiration times. Any object can be stored, for a given duration or forever, and the cache can be safely used by multiple goroutines.

Although zcache isn't meant to be used as a persistent datastore, the contents 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.

Index

Examples

Constants

View Source 
const (
	// NoExpiration indicates a cache item never expires.
	NoExpiration time.Duration = -1

	// DefaultExpiration indicates to use the cache default 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[K comparable, V any] struct {
	// contains filtered or unexported fields
}

Cache is a thread-safe in-memory key/value store.

Example (Any) 
// Create a new cache that stores any value, behaving similar to zcache v1
// or go-cache.
c := zcache.New[string, any](zcache.NoExpiration, zcache.NoExpiration)

c.Set("a", "value 1")
c.Set("b", 42)

a, _ := c.Get("a")
b, _ := c.Get("b")

// This needs type assertions.
p := func(a string, b int) { fmt.Println(a, b) }
p(a.(string), b.(int))

Output:

value 1 42
Example (Simple) 
// Create a cache with a default expiration time of 5 minutes, and which
// purges expired items every 10 minutes.
//
// This creates a cache with string keys and values, with Go 1.18 type
// parameters.
c := zcache.New[string, string](5*time.Minute, 10*time.Minute)

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

// Set the value of the key "baz" to "never", with no expiration time. The
// item won't be removed until it's removed with c.Delete("baz").
c.SetWithExpire("baz", "never", zcache.NoExpiration)

// Get the value associated with the key "foo" from the cache; due to the
// use of type parameters this is a string, and no type assertions are
// needed.
foo, ok := c.Get("foo")
if ok {
	fmt.Println(foo)
}

Output:

bar
Example (Struct) 
type MyStruct struct{ Value string }

// Create a new cache that stores a specific struct.
c := zcache.New[string, *MyStruct](zcache.NoExpiration, zcache.NoExpiration)
c.Set("cache", &MyStruct{Value: "value"})

v, _ := c.Get("cache")
fmt.Printf("%#v\n", v)

Output:

&zcache_test.MyStruct{Value:"value"}

func New 

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

New creates a new cache with a given expiration duration and cleanup interval.

If the expiration duration is less than 1 (or NoExpiration) the items in the cache never expire (by default) and must be deleted manually.

If the cleanup interval is less than 1 expired items are not deleted from the cache before calling c.DeleteExpired().

func NewFrom 

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

NewFrom creates a new cache like New() and populates the cache with the given items.

The passed map 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.

The map is *not* copied and 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() (which creates a copy of the map).

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 K, v V) error

Add an item to the cache only if it doesn't exist yet or if it has expired.

It will return an error if the cache key already exists.

func (Cache) AddWithExpire 

func (c Cache) AddWithExpire(k K, v V, d time.Duration) error

AddWithExpire adds an item to the cache only if it doesn't exist yet, or if it has expired.

It will return an error if the cache key already exists. 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) Delete 

func (c Cache) Delete(k K)

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

func (Cache) DeleteAll 

func (c Cache) DeleteAll() map[K]Item[V]

DeleteAll deletes all items from the cache and returns them.

This calls OnEvicted for returned items.

func (Cache) DeleteExpired 

func (c Cache) DeleteExpired()

DeleteExpired deletes all expired items from the cache.

func (Cache) DeleteFunc 

func (c Cache) DeleteFunc(filter func(key K, item Item[V]) (del, stop bool)) map[K]Item[V]

DeleteFunc deletes and returns cache items matched by the filter function.

The item will be deleted if the callback's first return argument is true. The loop will stop if the second return argument is true.

OnEvicted is called for deleted items.

func (Cache) Get 

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

Get an item from the cache.

Returns the item or the zero value and a bool indicating whether the key is set.

func (Cache) GetStale 

func (c Cache) GetStale(k K) (v V, expired bool, ok bool)

GetStale gets an item from the cache without checking if it's expired.

Returns the item or the zero value and a bool indicating whether the key was expired and a bool indicating whether the key was set.

func (Cache) GetWithExpire 

func (c Cache) GetWithExpire(k K) (V, time.Time, bool)

GetWithExpire returns an item and its expiration time from the cache.

It returns the item or the zero value, 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 set.

func (Cache) ItemCount 

func (c Cache) ItemCount() int

ItemCount 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[K]Item[V]

Items returns a copy of all unexpired items in the cache.

func (Cache) Keys 

func (c Cache) Keys() []K

Keys gets a list of all keys, in no particular order.

func (Cache) Modify 

func (c Cache) Modify(k K, f func(V) V) (V, bool)

Modify the value of an existing key.

This is thread-safe; for example to increment a number: 

cache.Modify("one", func(v int) int { return v + 1 })

Or setting a map key: 

cache.Modify("key", func(v map[string]string) map[string]string {
      v["k"] = "v"
      return v
})

This is thread-safe and can be safely run by multiple goroutines modifying the same key. If you would use Get() + Set() then two goroutines may Get() the same value and the modification of one of them will be lost.

This is not run for keys that are not set yet; the boolean return indicates if the key was set and if the function was applied.

func (Cache) OnEvicted 

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

OnEvicted sets an function to call when an item is evicted from the cache.

The function is run with the key and value. This is also run when a cache item is is deleted manually, but *not* when it is overwritten.

Can be set to nil to disable it (the default).

func (Cache) Pop 

func (c Cache) Pop(k K) (V, bool)

Pop gets an item from the cache and deletes it.

The bool return indicates if the item was set.

func (Cache) Rename added in v2.1.0 

func (c Cache) Rename(src, dst K) bool

Rename a key; the value and expiry will be left untouched; onEvicted will not be called.

Existing keys will be overwritten; returns false is the src key doesn't exist.

func (Cache) Replace 

func (c Cache) Replace(k K, v V) error

Replace sets a new value for the key only if it already exists and isn't expired.

It will return an error if the cache key doesn't exist.

func (Cache) ReplaceWithExpire 

func (c Cache) ReplaceWithExpire(k K, v V, d time.Duration) error

ReplaceWithExpire sets a new value for the key only if it already exists and isn't expired.

It will return an error if the cache key doesn't exist. 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) Reset 

func (c Cache) Reset()

Reset deletes all items from the cache without calling OnEvicted.

func (Cache) Set 

func (c Cache) Set(k K, v V)

Set a cache item, replacing any existing item.

func (Cache) SetWithExpire 

func (c Cache) SetWithExpire(k K, v V, d time.Duration)

SetWithExpire sets a cache item, 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) Touch 

func (c Cache) Touch(k K) (V, bool)

Touch replaces the expiry of a key with the default expiration and returns the current value, if any.

The boolean return value indicates if this item was set.

func (Cache) TouchWithExpire 

func (c Cache) TouchWithExpire(k K, d time.Duration) (V, bool)

TouchWithExpire replaces the expiry of a key and returns the current value, if any.

The boolean return value indicates if this item was set. 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[V any] struct {
	Object     V
	Expiration int64
}

Item stored in the cache; it holds the value and the expiration time as timestamp.

type Proxy 

type Proxy[ProxyK, MainK comparable, V any] struct {
	// contains filtered or unexported fields
}

Proxy a cache, allowing access to the same cache entries with different keys.

This is useful if you want to keep a cache which may be accessed by different keys in various different code paths. For example, a "site" may be accessed by ID or by CNAME. Proxy keys can have a different type than cache keys.

Proxy keys don't have an expiry and are never automatically deleted, the logic being that the same "proxy → key" mapping should always be valid. The items in the underlying cache can still be expired or deleted, and you can still manually call Delete() or Reset().

Example 
type Site struct {
	ID       int
	Hostname string
}

site := &Site{
	ID:       42,
	Hostname: "example.com",
}

// Create a new site which caches by site ID (int), and a "proxy" which
// caches by the hostname (string).
c := zcache.New[int, *Site](zcache.NoExpiration, zcache.NoExpiration)
p := zcache.NewProxy[string, int, *Site](c)

p.Set(42, "example.com", site)

siteByID, ok := c.Get(42)
fmt.Printf("%v %v\n", ok, siteByID)

siteByHost, ok := p.Get("example.com")
fmt.Printf("%v %v\n", ok, siteByHost)

// They're both the same object/pointer.
fmt.Printf("%v\n", siteByID == siteByHost)

Output:

true &{42 example.com}
true &{42 example.com}
true

func NewProxy 

func NewProxy[ProxyK, MainK comparable, V any](c *Cache[MainK, V]) *Proxy[ProxyK, MainK, V]

NewProxy creates a new proxied cache.

func (*Proxy[ProxyK, MainK, V]) Cache 

func (p *Proxy[ProxyK, MainK, V]) Cache() *Cache[MainK, V]

Cache gets the associated cache.

func (*Proxy[ProxyK, MainK, V]) Delete 

func (p *Proxy[ProxyK, MainK, V]) Delete(proxyKey ProxyK)

Delete stops proxying "proxyKey" to "mainKey".

This only removes the proxy link, not the entry from the main cache.

func (*Proxy[ProxyK, MainK, V]) Get 

func (p *Proxy[ProxyK, MainK, V]) Get(proxyKey ProxyK) (V, bool)

Get a proxied cache item with zcache.Cache.Get()

func (*Proxy[ProxyK, MainK, V]) Items 

func (p *Proxy[ProxyK, MainK, V]) Items() map[ProxyK]MainK

Items gets all items in this proxy, as proxyKey → mainKey

func (*Proxy[ProxyK, MainK, V]) Key 

func (p *Proxy[ProxyK, MainK, V]) Key(proxyKey ProxyK) (MainK, bool)

Key gets the main key for this proxied entry, if it exist.

The boolean value indicates if this proxy key is set.

func (*Proxy[ProxyK, MainK, V]) Proxy 

func (p *Proxy[ProxyK, MainK, V]) Proxy(mainKey MainK, proxyKey ProxyK)

Proxy items from "proxyKey" to "mainKey".

func (*Proxy[ProxyK, MainK, V]) Reset 

func (p *Proxy[ProxyK, MainK, V]) Reset()

Reset removes all proxied keys (but not the underlying cache).

func (*Proxy[ProxyK, MainK, V]) Set 

func (p *Proxy[ProxyK, MainK, V]) Set(mainKey MainK, proxyKey ProxyK, v V)

Set a new item in the main cache with the key mainKey, and proxy to that with proxyKey.

This behaves like zcache.Cache.Set() otherwise.

Source Files

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