lru.go

// This files was copied/modified from https://github.com/hashicorp/golang-lru
// which was (see below)

// This package provides a simple LRU cache. It is based on the
// LRU implementation in groupcache:
// https://github.com/golang/groupcache/tree/master/lru

package utils

import (
	"container/list"
	"sync"
	"time"
)

// Cache is a thread-safe fixed size LRU cache.
type Cache struct {
	size                   int
	evictList              *list.List
	items                  map[interface{}]*list.Element
	lock                   sync.RWMutex
	name                   string
	defaultExpiry          int64
	invalidateClusterEvent string
	currentGeneration      int64
	len                    int
}

// entry is used to hold a value in the evictList.
type entry struct {
	key        interface{}
	value      interface{}
	expires    time.Time
	generation int64
}

// New creates an LRU of the given size.
func NewLru(size int) *Cache {
	return &Cache{
		size:      size,
		evictList: list.New(),
		items:     make(map[interface{}]*list.Element, size),
	}
}

// New creates an LRU with the given parameters.
func NewLruWithParams(size int, name string, defaultExpiry int64, invalidateClusterEvent string) *Cache {
	lru := NewLru(size)
	lru.name = name
	lru.defaultExpiry = defaultExpiry
	lru.invalidateClusterEvent = invalidateClusterEvent
	return lru
}

// Purge is used to completely clear the cache.
func (c *Cache) Purge() {
	c.lock.Lock()
	defer c.lock.Unlock()

	c.len = 0
	c.currentGeneration++
}

// Add adds the given key and value to the store without an expiry.
func (c *Cache) Add(key, value interface{}) {
	c.AddWithExpiresInSecs(key, value, 0)
}

// Add adds the given key and value to the store with the default expiry.
func (c *Cache) AddWithDefaultExpires(key, value interface{}) {
	c.AddWithExpiresInSecs(key, value, c.defaultExpiry)
}

// AddWithExpiresInSecs adds the given key and value to the cache with the given expiry.
func (c *Cache) AddWithExpiresInSecs(key, value interface{}, expireAtSecs int64) {
	c.lock.Lock()
	defer c.lock.Unlock()

	c.add(key, value, time.Duration(expireAtSecs)*time.Second)
}

func (c *Cache) add(key, value interface{}, ttl time.Duration) {
	var expires time.Time
	if ttl > 0 {
		expires = time.Now().Add(ttl)
	}

	// Check for existing item, ignoring expiry since we'd update anyway.
	if ent, ok := c.items[key]; ok {
		c.evictList.MoveToFront(ent)
		e := ent.Value.(*entry)
		e.value = value
		e.expires = expires
		if e.generation != c.currentGeneration {
			e.generation = c.currentGeneration
			c.len++
		}
		return
	}

	// Add new item
	ent := &entry{key, value, expires, c.currentGeneration}
	entry := c.evictList.PushFront(ent)
	c.items[key] = entry
	c.len++

	if c.evictList.Len() > c.size {
		c.removeElement(c.evictList.Back())
	}
}

// Get returns the value stored in the cache for a key, or nil if no value is present. The ok result indicates whether value was found in the cache.
func (c *Cache) Get(key interface{}) (value interface{}, ok bool) {
	c.lock.Lock()
	defer c.lock.Unlock()

	return c.getValue(key)
}

func (c *Cache) getValue(key interface{}) (value interface{}, ok bool) {
	if ent, ok := c.items[key]; ok {
		e := ent.Value.(*entry)

		if e.generation != c.currentGeneration || (!e.expires.IsZero() && time.Now().After(e.expires)) {
			c.removeElement(ent)
			return nil, false
		}

		c.evictList.MoveToFront(ent)
		return ent.Value.(*entry).value, true
	}

	return nil, false
}

// GetOrAdd returns the existing value for the key if present. Otherwise, it stores and returns the given value. The loaded result is true if the value was loaded, false if stored.
// This API intentionally deviates from the Add-only variants above for simplicity. We should simplify the entire API in the future.
func (c *Cache) GetOrAdd(key, value interface{}, ttl time.Duration) (actual interface{}, loaded bool) {
	c.lock.Lock()
	defer c.lock.Unlock()

	// Check for existing item
	if actualValue, ok := c.getValue(key); ok {
		return actualValue, true
	}

	c.add(key, value, ttl)

	return value, false
}

// Remove deletes the value for a key.
func (c *Cache) Remove(key interface{}) {
	c.lock.Lock()
	defer c.lock.Unlock()

	if ent, ok := c.items[key]; ok {
		c.removeElement(ent)
	}
}

// Keys returns a slice of the keys in the cache, from oldest to newest.
func (c *Cache) Keys() []interface{} {
	c.lock.RLock()
	defer c.lock.RUnlock()

	keys := make([]interface{}, c.len)
	i := 0
	for ent := c.evictList.Back(); ent != nil; ent = ent.Prev() {
		e := ent.Value.(*entry)
		if e.generation == c.currentGeneration {
			keys[i] = e.key
			i++
		}
	}

	return keys
}

// Len returns the number of items in the cache.
func (c *Cache) Len() int {
	c.lock.RLock()
	defer c.lock.RUnlock()
	return c.len
}

// Name identifies this cache instance among others in the system.
func (c *Cache) Name() string {
	return c.name
}

// GetInvalidateClusterEvent returns the cluster event configured when this cache was created.
func (c *Cache) GetInvalidateClusterEvent() string {
	return c.invalidateClusterEvent
}

func (c *Cache) removeElement(e *list.Element) {
	c.evictList.Remove(e)
	kv := e.Value.(*entry)
	if kv.generation == c.currentGeneration {
		c.len--
	}
	delete(c.items, kv.key)
}