cache/cache.go

package cache

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

type unexportedInterface interface {
	Set(string, interface{}, time.Duration)
	Add(string, interface{}, time.Duration) error
	Replace(string, interface{}, time.Duration) error
	Get(string) (interface{}, bool)
	Increment(string, int64) error
	IncrementInt(string, int) (int, error)
	IncrementInt8(string, int8) (int8, error)
	IncrementInt16(string, int16) (int16, error)
	IncrementInt32(string, int32) (int32, error)
	IncrementInt64(string, int64) (int64, error)
	IncrementUint(string, uint) (uint, error)
	IncrementUintptr(string, uintptr) (uintptr, error)
	IncrementUint8(string, uint8) (uint8, error)
	IncrementUint16(string, uint16) (uint16, error)
	IncrementUint32(string, uint32) (uint32, error)
	IncrementUint64(string, uint64) (uint64, error)
	IncrementFloat(string, float64) error
	IncrementFloat32(string, float32) (float32, error)
	IncrementFloat64(string, float64) (float64, error)
	Decrement(string, int64) error
	DecrementInt(string, int) (int, error)
	DecrementInt8(string, int8) (int8, error)
	DecrementInt16(string, int16) (int16, error)
	DecrementInt32(string, int32) (int32, error)
	DecrementInt64(string, int64) (int64, error)
	DecrementUint(string, uint) (uint, error)
	DecrementUintptr(string, uintptr) (uintptr, error)
	DecrementUint8(string, uint8) (uint8, error)
	DecrementUint16(string, uint16) (uint16, error)
	DecrementUint32(string, uint32) (uint32, error)
	DecrementUint64(string, uint64) (uint64, error)
	DecrementFloat(string, float64) error
	DecrementFloat32(string, float32) (float32, error)
	DecrementFloat64(string, float64) (float64, error)
	Delete(string)
	DeleteExpired()
	Items() map[string]*Item
	ItemCount() int
	Flush()
	Save(io.Writer) error
	SaveFile(string) error
	Load(io.Reader) error
	LoadFile(io.Reader) error
}

type Item struct {
	Object     interface{}
	Expiration *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())
}

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
}

// Add an item to the cache, replacing any existing item. If the duration is 0,
// the cache's default expiration time is used. If it is -1, 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
	if d == 0 {
		d = c.defaultExpiration
	}
	if d > 0 {
		t := time.Now().Add(d)
		e = &t
	}
	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
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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")
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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)
	}
	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.
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.
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.
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.
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
// field of the items should be checked.
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
}

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

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) *cache {
	if de == 0 {
		de = -1
	}
	c := &cache{
		defaultExpiration: de,
		items:             map[string]*Item{},
	}
	return c
}

// Return a new cache with a given default expiration duration and cleanup
// interval. If the expiration duration is less than 1, 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 DeleteExpired.
func New(defaultExpiration, cleanupInterval time.Duration) *Cache {
	c := newCache(defaultExpiration)
	// 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 cleanupInterval > 0 {
		runJanitor(c, cleanupInterval)
		runtime.SetFinalizer(C, stopJanitor)
	}
	return C
}

type unexportedShardedCache struct {
	*shardedCache
}

type shardedCache struct {
	m       uint32
	cs      []*cache
	janitor *shardedJanitor
}

func (sc *shardedCache) bucket(k string) *cache {
	h := fnv.New32()
	h.Write([]byte(k))
	n := binary.BigEndian.Uint32(h.Sum(nil))
	return sc.cs[n%sc.m]
}

func (sc *shardedCache) Set(k string, x interface{}, d time.Duration) {
	sc.bucket(k).Set(k, x, d)
}

func (sc *shardedCache) Add(k string, x interface{}, d time.Duration) error {
	return sc.bucket(k).Add(k, x, d)
}

func (sc *shardedCache) Replace(k string, x interface{}, d time.Duration) error {
	return sc.bucket(k).Replace(k, x, d)
}

func (sc *shardedCache) Get(k string) (interface{}, bool) {
	return sc.bucket(k).Get(k)
}

func (sc *shardedCache) Increment(k string, n int64) error {
	return sc.bucket(k).Increment(k, n)
}

func (sc *shardedCache) IncrementFloat(k string, n float64) error {
	return sc.bucket(k).IncrementFloat(k, n)
}

func (sc *shardedCache) Decrement(k string, n int64) error {
	return sc.bucket(k).Decrement(k, n)
}

func (sc *shardedCache) Delete(k string) {
	sc.bucket(k).Delete(k)
}

func (sc *shardedCache) DeleteExpired() {
	for _, v := range sc.cs {
		v.DeleteExpired()
	}
}

func (sc *shardedCache) Flush() {
	for _, v := range sc.cs {
		v.Flush()
	}
}

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

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

func stopShardedJanitor(sc *unexportedShardedCache) {
	sc.janitor.stop <- true
}

func runShardedJanitor(sc *shardedCache, ci time.Duration) {
	j := &shardedJanitor{
		Interval: ci,
	}
	sc.janitor = j
	go j.Run(sc)
}

func newShardedCache(n int, de time.Duration) *shardedCache {
	sc := &shardedCache{
		m:  uint32(n - 1),
		cs: make([]*cache, n),
	}
	for i := 0; i < n; i++ {
		c := &cache{
			defaultExpiration: de,
			items:             map[string]*Item{},
		}
		sc.cs[i] = c
	}
	return sc
}

func unexportedNewSharded(shards int, defaultExpiration, cleanupInterval time.Duration) *unexportedShardedCache {
	if defaultExpiration == 0 {
		defaultExpiration = -1
	}
	sc := newShardedCache(shards, defaultExpiration)
	SC := &unexportedShardedCache{sc}
	if cleanupInterval > 0 {
		runShardedJanitor(sc, cleanupInterval)
		runtime.SetFinalizer(SC, stopShardedJanitor)
	}
	return SC
}