go-cache/cache.go

package cache

import (
	"encoding/gob"
	"fmt"
	"io"
	"os"
	"runtime"
	"sync"
	"time"
)

type Item struct {
	Object     interface{}
	Expiration *time.Time
	Ctime      *time.Time
	Atime      *time.Time
}

// Returns true if the item has expired.
func (item *Item) Expired() bool {
	if item.Expiration == nil {
		return false
	}
	return item.Expiration.Before(time.Now())
}

// Return the Atime
func (item *Item) LastAccessed() *time.Time {
	return item.Atime
}

func (item *Item) Accessed() {
	now := time.Now()
	item.Atime = &now
}

// Return the Ctime
func (item *Item) Created() *time.Time {
	return item.Ctime
}

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
)

type Cache struct {
	*cache
	// If this is confusing, see the comment at the bottom of New()
}

type cache struct {
	sync.RWMutex
	defaultExpiration time.Duration
	items             map[string]*Item
	janitor           *janitor
	maxItems          int
}

// 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.
func (c *cache) Set(k string, x interface{}, d time.Duration) {
	c.Lock()
	c.set(k, x, d)
	// TODO: Calls to mu.Unlock are currently not deferred because defer
	// adds ~200 ns (as of go1.)
	c.Unlock()
}

func (c *cache) set(k string, x interface{}, d time.Duration) {
	var e *time.Time
	t := time.Now()
	at := &t
	ct := &t
	
	if d == DefaultExpiration {
		d = c.defaultExpiration
	}
	if d > 0 {
		t = time.Now().Add(d)
		e = &t
	}
	
	if c.maxItems > 0 {
		// We don't want to hit the expiration if we're updating.
		_, found := c.get(k)
		if ! found {
			// Create, means maybe expire
			c.ExpireLRU() 
		} else {
			// Update, means don't expire, or change the Ctime
			ct = c.items[k].Created() 	
		}
		c.items[k] = &Item{
			Object:     x,
			Expiration: e,
			Ctime:      ct,
			Atime:      at,
		}
	} else {
		// Not using maxItems
		c.items[k] = &Item{
			Object:     x,
			Expiration: e,
		}
	}
}

// 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 (c *cache) Add(k string, x interface{}, d time.Duration) error {
	c.Lock()
	_, found := c.get(k)
	if found {
		c.Unlock()
		return fmt.Errorf("Item %s already exists", k)
	}
	c.set(k, x, d)
	c.Unlock()
	return nil
}

// 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 (c *cache) Replace(k string, x interface{}, d time.Duration) error {
	c.Lock()
	_, found := c.get(k)
	if !found {
		c.Unlock()
		return fmt.Errorf("Item %s doesn't exist", k)
	}
	c.set(k, x, d)
	c.Unlock()
	return nil
}

// Get an item from the cache. Returns the item or nil, and a bool indicating
// whether the key was found.
func (c *cache) Get(k string) (interface{}, bool) {
	c.RLock()
	x, found := c.get(k)
	c.RUnlock()
	return x, found
}

func (c *cache) get(k string) (interface{}, bool) {
	item, found := c.items[k]
	if !found || item.Expired() {
		return nil, false
	}
	
	if c.maxItems > 0 { item.Accessed() }
	
	return item.Object, true
}

// 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 (c *cache) Increment(k string, n int64) error {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	switch v.Object.(type) {
	case int:
		v.Object = v.Object.(int) + int(n)
	case int8:
		v.Object = v.Object.(int8) + int8(n)
	case int16:
		v.Object = v.Object.(int16) + int16(n)
	case int32:
		v.Object = v.Object.(int32) + int32(n)
	case int64:
		v.Object = v.Object.(int64) + n
	case uint:
		v.Object = v.Object.(uint) + uint(n)
	case uintptr:
		v.Object = v.Object.(uintptr) + uintptr(n)
	case uint8:
		v.Object = v.Object.(uint8) + uint8(n)
	case uint16:
		v.Object = v.Object.(uint16) + uint16(n)
	case uint32:
		v.Object = v.Object.(uint32) + uint32(n)
	case uint64:
		v.Object = v.Object.(uint64) + uint64(n)
	case float32:
		v.Object = v.Object.(float32) + float32(n)
	case float64:
		v.Object = v.Object.(float64) + float64(n)
	default:
		c.Unlock()
		return fmt.Errorf("The value for %s is not an integer", k)
	}
	c.Unlock()
	return nil
}

// 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 (c *cache) IncrementFloat(k string, n float64) error {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	switch v.Object.(type) {
	case float32:
		v.Object = v.Object.(float32) + float32(n)
	case float64:
		v.Object = v.Object.(float64) + n
	default:
		c.Unlock()
		return fmt.Errorf("The value for %s does not have type float32 or float64", k)
	}
	c.Unlock()
	return nil
}

// 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 (c *cache) IncrementInt(k string, n int) (int, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(int)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an int", k)
	}
	nv := rv + n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) IncrementInt8(k string, n int8) (int8, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(int8)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an int8", k)
	}
	nv := rv + n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) IncrementInt16(k string, n int16) (int16, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(int16)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an int16", k)
	}
	nv := rv + n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) IncrementInt32(k string, n int32) (int32, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(int32)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an int32", k)
	}
	nv := rv + n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) IncrementInt64(k string, n int64) (int64, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(int64)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an int64", k)
	}
	nv := rv + n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) IncrementUint(k string, n uint) (uint, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(uint)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an uint", k)
	}
	nv := rv + n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) IncrementUintptr(k string, n uintptr) (uintptr, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(uintptr)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an uintptr", k)
	}
	nv := rv + n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) IncrementUint8(k string, n uint8) (uint8, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(uint8)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an uint8", k)
	}
	nv := rv + n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) IncrementUint16(k string, n uint16) (uint16, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}

	if c.maxItems > 0 { v.Accessed() }

	rv, ok := v.Object.(uint16)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an uint16", k)
	}
	nv := rv + n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) IncrementUint32(k string, n uint32) (uint32, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(uint32)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an uint32", k)
	}
	nv := rv + n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) IncrementUint64(k string, n uint64) (uint64, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(uint64)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an uint64", k)
	}
	nv := rv + n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) IncrementFloat32(k string, n float32) (float32, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(float32)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an float32", k)
	}
	nv := rv + n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) IncrementFloat64(k string, n float64) (float64, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(float64)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an float64", k)
	}
	nv := rv + n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) Decrement(k string, n int64) error {
	// TODO: Implement Increment and Decrement more cleanly.
	// (Cannot do Increment(k, n*-1) for uints.)
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return fmt.Errorf("Item not found")
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	switch v.Object.(type) {
	case int:
		v.Object = v.Object.(int) - int(n)
	case int8:
		v.Object = v.Object.(int8) - int8(n)
	case int16:
		v.Object = v.Object.(int16) - int16(n)
	case int32:
		v.Object = v.Object.(int32) - int32(n)
	case int64:
		v.Object = v.Object.(int64) - n
	case uint:
		v.Object = v.Object.(uint) - uint(n)
	case uintptr:
		v.Object = v.Object.(uintptr) - uintptr(n)
	case uint8:
		v.Object = v.Object.(uint8) - uint8(n)
	case uint16:
		v.Object = v.Object.(uint16) - uint16(n)
	case uint32:
		v.Object = v.Object.(uint32) - uint32(n)
	case uint64:
		v.Object = v.Object.(uint64) - uint64(n)
	case float32:
		v.Object = v.Object.(float32) - float32(n)
	case float64:
		v.Object = v.Object.(float64) - float64(n)
	default:
		c.Unlock()
		return fmt.Errorf("The value for %s is not an integer", k)
	}
	c.Unlock()
	return nil
}

// 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 (c *cache) DecrementFloat(k string, n float64) error {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return fmt.Errorf("Item %s not found", k)
	}

	if c.maxItems > 0 { v.Accessed() }
	
	switch v.Object.(type) {
	case float32:
		v.Object = v.Object.(float32) - float32(n)
	case float64:
		v.Object = v.Object.(float64) - n
	default:
		c.Unlock()
		return fmt.Errorf("The value for %s does not have type float32 or float64", k)
	}
	c.Unlock()
	return nil
}

// 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 (c *cache) DecrementInt(k string, n int) (int, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(int)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an int", k)
	}
	nv := rv - n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) DecrementInt8(k string, n int8) (int8, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(int8)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an int8", k)
	}
	nv := rv - n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) DecrementInt16(k string, n int16) (int16, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(int16)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an int16", k)
	}
	nv := rv - n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) DecrementInt32(k string, n int32) (int32, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(int32)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an int32", k)
	}
	nv := rv - n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) DecrementInt64(k string, n int64) (int64, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(int64)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an int64", k)
	}
	nv := rv - n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) DecrementUint(k string, n uint) (uint, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(uint)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an uint", k)
	}
	nv := rv - n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) DecrementUintptr(k string, n uintptr) (uintptr, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(uintptr)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an uintptr", k)
	}
	nv := rv - n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) DecrementUint8(k string, n uint8) (uint8, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(uint8)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an uint8", k)
	}
	nv := rv - n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) DecrementUint16(k string, n uint16) (uint16, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(uint16)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an uint16", k)
	}
	nv := rv - n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) DecrementUint32(k string, n uint32) (uint32, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(uint32)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an uint32", k)
	}
	nv := rv - n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) DecrementUint64(k string, n uint64) (uint64, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}

	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(uint64)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an uint64", k)
	}
	nv := rv - n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) DecrementFloat32(k string, n float32) (float32, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(float32)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an float32", k)
	}
	nv := rv - n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// 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 (c *cache) DecrementFloat64(k string, n float64) (float64, error) {
	c.Lock()
	v, found := c.items[k]
	if !found || v.Expired() {
		c.Unlock()
		return 0, fmt.Errorf("Item %s not found", k)
	}
	
	if c.maxItems > 0 { v.Accessed() }
	
	rv, ok := v.Object.(float64)
	if !ok {
		c.Unlock()
		return 0, fmt.Errorf("The value for %s is not an float64", k)
	}
	nv := rv - n
	v.Object = nv
	c.Unlock()
	return nv, nil
}

// Delete an item from the cache. Does nothing if the key is not in the cache.
func (c *cache) Delete(k string) {
	c.Lock()
	c.delete(k)
	c.Unlock()
}

func (c *cache) delete(k string) {
	delete(c.items, k)
}

// Delete all expired items from the cache.
func (c *cache) DeleteExpired() {
	c.Lock()
	for k, v := range c.items {
		if v.Expired() {
			c.delete(k)
		}
	}
	c.Unlock()
}

// 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 (c *cache) Save(w io.Writer) (err error) {
	enc := gob.NewEncoder(w)
	defer func() {
		if x := recover(); x != nil {
			err = fmt.Errorf("Error registering item types with Gob library")
		}
	}()
	c.RLock()
	defer c.RUnlock()
	for _, v := range c.items {
		gob.Register(v.Object)
	}
	err = enc.Encode(&c.items)
	return
}

// 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 (c *cache) SaveFile(fname string) error {
	fp, err := os.Create(fname)
	if err != nil {
		return err
	}
	err = c.Save(fp)
	if err != nil {
		fp.Close()
		return err
	}
	return fp.Close()
}

// 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 (c *cache) Load(r io.Reader) error {
	dec := gob.NewDecoder(r)
	items := map[string]*Item{}
	err := dec.Decode(&items)
	if err == nil {
		c.Lock()
		defer c.Unlock()
		for k, v := range items {
			ov, found := c.items[k]
			if !found || ov.Expired() {
				c.items[k] = v
			}
		}
	}
	return err
}

// 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 (c *cache) LoadFile(fname string) error {
	fp, err := os.Open(fname)
	if err != nil {
		return err
	}
	err = c.Load(fp)
	if err != nil {
		fp.Close()
		return err
	}
	return fp.Close()
}

// 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 (c *cache) Items() map[string]*Item {
	c.RLock()
	defer c.RUnlock()
	return c.items
}

// 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 (c *cache) ItemCount() int {
	c.RLock()
	n := len(c.items)
	c.RUnlock()
	return n
}

// Returns the number of items in the cache *that have not expired*
func (c *cache) itemCount() int {
	n := 0
	now := time.Now()
	
	for _, v := range c.items {
		if v.Expiration == nil || ! v.Expiration.Before(now) {
			n++
		}
	}
	return n
}

// Delete all items from the cache.
func (c *cache) Flush() {
	c.Lock()
	c.items = map[string]*Item{}
	c.Unlock()
}

// Find oldest N items, and Expire them.
// Returns the number "expired".
// BIG HAIRY ALERT: This function assumes it is called
// from inside a c.Lock() .. c.Unlock() block. 
func (c *cache) ExpireLRU() {

	// We need the number of UNexpired Items
	itemCount := c.itemCount()

	if itemCount >= c.maxItems {
	
		// Cache the current time.
		// We do this "early" so that when we set an Expiration,
		// it is definitely "do" when the janitor ticks
		notw := time.Now()

		var lastTime int64 = 0
		var lastName string = ""

		for k, v := range c.items {
			if v.Expired() == false {
				// unexpired item
				
				atime := v.LastAccessed().UnixNano()
				if lastTime == 0 {
					// We need to expire something, so let's start with the first item
					lastTime = atime
					lastName = k
				} else if atime < lastTime {
					// We found a least-recently-used item
					lastTime = atime
					lastName = k
				}
			}
		}
		
		if lastTime > 0 {
			// We expire the item, but making it look .Expired(), 
			// so the janitor will clean it up for us
			c.items[lastName].Expiration = &notw
		}
	}
}

type janitor struct {
	Interval time.Duration
	stop     chan bool
}

func (j *janitor) Run(c *cache) {
	j.stop = make(chan bool)
	tick := time.Tick(j.Interval)
	for {
		select {
		case <-tick:
			c.DeleteExpired()
		case <-j.stop:
			return
		}
	}
}

func stopJanitor(c *Cache) {
	c.janitor.stop <- true
}

func runJanitor(c *cache, ci time.Duration) {
	j := &janitor{
		Interval: ci,
	}
	c.janitor = j
	go j.Run(c)
}

func newCache(de time.Duration, m map[string]*Item, mi int) *cache {
	if de == 0 {
		de = -1
	}
	c := &cache{
		defaultExpiration: de,
		maxItems:          mi,
		items:             m,
	}
	return c
}

func newCacheWithJanitor(de time.Duration, ci time.Duration, m map[string]*Item, mi int) *Cache {
	c := newCache(de, m, mi)
	// This trick ensures that the janitor goroutine (which--granted it
	// was enabled--is running DeleteExpired on c forever) does not keep
	// the returned C object from being garbage collected. When it is
	// garbage collected, the finalizer stops the janitor goroutine, after
	// which c can be collected.
	C := &Cache{c}
	if ci > 0 {
		runJanitor(c, ci)
		runtime.SetFinalizer(C, stopJanitor)
	}
	return C
}

// 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 New(defaultExpiration, cleanupInterval time.Duration,  maxItems int) *Cache {
	items := make(map[string]*Item)
	return newCacheWithJanitor(defaultExpiration, cleanupInterval, items, maxItems)
}

// 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 NewFrom(defaultExpiration, cleanupInterval time.Duration, items map[string]*Item, maxItems int) *Cache {
	return newCacheWithJanitor(defaultExpiration, cleanupInterval, items, maxItems)
}