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cache.go
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cache.go
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package main
import (
"container/list"
"fmt"
"time"
)
type lruObject struct {
Key interface{}
Value interface{}
Expiry time.Time
}
// LRUCache implements an LRU cache.
type LRUCache struct {
cap int
items *list.List
lookup map[interface{}]*list.Element
expiry time.Duration
}
type cacheError struct{}
func (ce cacheError) Error() string {
return "Cache Miss"
}
var miss cacheError
// NewLRUCache returns a new LRUCache object with capacity cap and expiration time of exp.
func NewLRUCache(cap int, exp string) (*LRUCache, error) {
expiry, err := time.ParseDuration(exp)
if err != nil {
return nil, err
}
c := new(LRUCache)
c.cap = cap
c.items = list.New()
c.lookup = make(map[interface{}]*list.Element, cap)
c.expiry = expiry
return c, nil
}
// Must will panis if there is an error. Used as cache = Must(NewLRUCache(...)) for
// initialization.
func Must(c *LRUCache, e error) *LRUCache {
if e != nil {
panic(e)
}
return c
}
// Get tries to retrive the object corresponding to the key from the cache.
func (c *LRUCache) Get(k interface{}) (interface{}, error) {
e := c.lookup[k]
if e == nil {
fmt.Println("MISS")
return nil, miss
}
o := e.Value.(lruObject)
if o.Expiry.Before(time.Now()) {
delete(c.lookup, k)
c.items.Remove(e)
fmt.Println("MISS")
return nil, miss
}
fmt.Println("HIT")
c.items.MoveToFront(e)
return o.Value, nil
}
// Set places the object in the cache.
func (c *LRUCache) Set(k interface{}, v interface{}) {
if c.cap <= c.items.Len() {
delete(c.lookup, c.items.Back().Value.(lruObject).Key)
c.items.Remove(c.items.Back())
}
e := c.items.PushFront(lruObject{Key: k, Value: v, Expiry: time.Now().Add(c.expiry)})
c.lookup[k] = e
}
var fibCache = Must(NewLRUCache(20, "100ms"))
func fib(n int) int {
c, err := fibCache.Get(n)
if err == nil {
return c.(int)
}
if n <= 2 {
return 1
}
v := fib(n-1) + fib(n-2)
fibCache.Set(n, v)
return v
}
func main() {
cache, _ := NewLRUCache(10, "5s")
cache.Set("a", 4)
v, _ := cache.Get("a")
fmt.Printf("Got: %d\n", v.(int))
fmt.Printf("fib(5): %d\n", fib(5))
fmt.Printf("fib(6): %d\n", fib(6))
fmt.Printf("fib(100): %d\n", fib(100))
for i := 0; i < 11; i++ {
c := 'a' + i
cache.Set(i, c)
fmt.Printf("i: %c\n", c)
}
for i := 0; i < 11; i++ {
v, err := cache.Get(i)
var c rune
if err == nil {
c = v.(rune)
} else {
c = rune('a' + i)
cache.Set(i, c)
}
fmt.Printf("i: %c\n", c)
}
for i := 10; i >= 0; i-- {
v, err := cache.Get(i)
var c rune
if err == nil {
c = v.(rune)
} else {
c = rune('a' + i)
cache.Set(i, c)
}
fmt.Printf("i: %c\n", c)
}
}