134 lines
3.3 KiB
Go
134 lines
3.3 KiB
Go
// Package cache implements a simple cache where the entries are
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// expired after a given time (5 minutes of disuse by default).
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package cache
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import (
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"sync"
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"time"
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)
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// Cache holds values indexed by string, but expired after a given (5
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// minutes by default).
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type Cache struct {
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mu sync.Mutex
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cache map[string]*cacheEntry
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expireRunning bool
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expireDuration time.Duration // expire the cache entry when it is older than this
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expireInterval time.Duration // interval to run the cache expire
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}
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// New creates a new cache with the default expire duration and interval
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func New() *Cache {
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return &Cache{
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cache: map[string]*cacheEntry{},
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expireRunning: false,
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expireDuration: 300 * time.Second,
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expireInterval: 60 * time.Second,
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}
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}
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// cacheEntry is stored in the cache
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type cacheEntry struct {
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value interface{} // cached item
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err error // creation error
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key string // key
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lastUsed time.Time // time used for expiry
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}
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// CreateFunc is called to create new values. If the create function
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// returns an error it will be cached if ok is true, otherwise the
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// error will just be returned, allowing negative caching if required.
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type CreateFunc func(key string) (value interface{}, ok bool, error error)
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// used marks an entry as accessed now and kicks the expire timer off
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// should be called with the lock held
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func (c *Cache) used(entry *cacheEntry) {
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entry.lastUsed = time.Now()
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if !c.expireRunning {
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time.AfterFunc(c.expireInterval, c.cacheExpire)
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c.expireRunning = true
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}
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}
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// Get gets a value named key either from the cache or creates it
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// afresh with the create function.
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func (c *Cache) Get(key string, create CreateFunc) (value interface{}, err error) {
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c.mu.Lock()
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entry, ok := c.cache[key]
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if !ok {
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c.mu.Unlock() // Unlock in case Get is called recursively
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value, ok, err = create(key)
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if err != nil && !ok {
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return value, err
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}
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entry = &cacheEntry{
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value: value,
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key: key,
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err: err,
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}
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c.mu.Lock()
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c.cache[key] = entry
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}
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defer c.mu.Unlock()
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c.used(entry)
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return entry.value, entry.err
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}
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// Put puts an value named key into the cache
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func (c *Cache) Put(key string, value interface{}) {
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c.mu.Lock()
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defer c.mu.Unlock()
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entry := &cacheEntry{
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value: value,
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key: key,
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}
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c.used(entry)
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c.cache[key] = entry
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}
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// GetMaybe returns the key and true if found, nil and false if not
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func (c *Cache) GetMaybe(key string) (value interface{}, found bool) {
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c.mu.Lock()
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defer c.mu.Unlock()
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entry, found := c.cache[key]
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if !found {
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return nil, found
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}
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c.used(entry)
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return entry.value, found
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}
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// cacheExpire expires any entries that haven't been used recently
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func (c *Cache) cacheExpire() {
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c.mu.Lock()
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defer c.mu.Unlock()
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now := time.Now()
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for key, entry := range c.cache {
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if now.Sub(entry.lastUsed) > c.expireDuration {
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delete(c.cache, key)
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}
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}
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if len(c.cache) != 0 {
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time.AfterFunc(c.expireInterval, c.cacheExpire)
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c.expireRunning = true
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} else {
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c.expireRunning = false
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}
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}
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// Clear removes everything from the cahce
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func (c *Cache) Clear() {
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c.mu.Lock()
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for k := range c.cache {
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delete(c.cache, k)
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}
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c.mu.Unlock()
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}
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// Entries returns the number of entries in the cache
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func (c *Cache) Entries() int {
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c.mu.Lock()
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entries := len(c.cache)
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c.mu.Unlock()
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return entries
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}
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