go-vise

cache.go (5341B)

---

 package cache
 
 import (
 	"fmt"
 )
 
 // Cache stores loaded content, enforcing size limits and keeping track of size usage.
 //
 // TODO: hide values from client, while allowing cbor serialization
 type Cache struct {
 	// Total allowed cumulative size of values (not code) in cache
 	CacheSize uint32
 	// Currently used bytes by all values (not code) in cache
 	CacheUseSize uint32
 	// All loaded cache items
 	Cache []map[string]string
 	// Size limits for all loaded symbols.
 	Sizes map[string]uint16
 	// Last inserted value (regardless of scope)
 	LastValue string 
 	invalid bool
 }
 
 // NewCache creates a new ready-to-use Cache object
 func NewCache() *Cache {
 	ca := &Cache{
 		Cache: []map[string]string{make(map[string]string)},
 		Sizes: make(map[string]uint16),
 	}
 	return ca
 }
 
 // Invalidate implements the Memory interface.
 func(ca *Cache) Invalidate() {
 	ca.invalid = true
 }
 
 // Invalid implements the Memory interface.
 func(ca *Cache) Invalid() bool {
 	return ca.invalid
 }
 
 // WithCacheSize is a chainable method that applies a cumulative cache size limitation for all cached items.
 func(ca *Cache) WithCacheSize(cacheSize uint32) *Cache {
 	ca.CacheSize = cacheSize
 	return ca
 }
 
 // Add implements the Memory interface.
 func(ca *Cache) Add(key string, value string, sizeLimit uint16) error {
 	if sizeLimit > 0 {
 		l := uint16(len(value))
 		if l > sizeLimit {
 			return fmt.Errorf("value length %v exceeds value size limit %v", l, sizeLimit)
 		}
 	}
 	checkFrame := ca.frameOf(key)
 	if checkFrame > -1 {
 		thisFrame := len(ca.Cache) - 1
 		if checkFrame == thisFrame {
 			return ErrDup
 		}
 		return fmt.Errorf("key %v already defined in frame %v, this is frame %v", key, checkFrame, thisFrame)
 	}
 	var sz uint32
 	if len(value) > 0 {
 		sz = ca.checkCapacity(value)
 		if sz == 0 {
 			return fmt.Errorf("Cache capacity exceeded %v of %v", ca.CacheUseSize + sz, ca.CacheSize)
 		}
 	}
 	logg.Infof("Cache add", "key", key, "size", sz, "limit", sizeLimit)
 	logg.Tracef("", "Cache add data", value)
 	ca.Cache[len(ca.Cache)-1][key] = value
 	ca.CacheUseSize += sz
 	ca.Sizes[key] = sizeLimit
 	ca.LastValue = value
 	return nil
 }
 
 // ReservedSize implements the Memory interface.
 func(ca *Cache) ReservedSize(key string) (uint16, error) {
 	v, ok := ca.Sizes[key]
 	if !ok {
 		return 0, fmt.Errorf("unknown symbol: %s", key)
 	}
 	return v, nil
 }
 
 // Update implements the Memory interface.
 func(ca *Cache) Update(key string, value string) error {
 	sizeLimit := ca.Sizes[key]
 	if ca.Sizes[key] > 0 {
 		l := uint16(len(value))
 		if l > sizeLimit {
 			return fmt.Errorf("update value length %v exceeds value size limit %v", l, sizeLimit)
 		}
 	}
 	checkFrame := ca.frameOf(key)
 	if checkFrame == -1 {
 		return fmt.Errorf("key %v not defined", key)
 	}
 	r := ca.Cache[checkFrame][key]
 	l := uint32(len(r))
 	ca.Cache[checkFrame][key] = ""
 	ca.CacheUseSize -= l
 	sz := ca.checkCapacity(value)
 	if sz == 0 {
 		baseUseSize := ca.CacheUseSize
 		ca.Cache[checkFrame][key] = r
 		ca.CacheUseSize += l
 		return fmt.Errorf("Cache capacity exceeded %v of %v", baseUseSize + sz, ca.CacheSize)
 	}
 	ca.Cache[checkFrame][key] = value
 	ca.CacheUseSize += uint32(len(value))
 	return nil
 }
 
 // Get implements the Memory interface.
 func(ca *Cache) Get(key string) (string, error) {
 	i := ca.frameOf(key)
 	if i == -1 {
 		return "", fmt.Errorf("key '%s' not found in any frame", key)
 	}
 	r, ok := ca.Cache[i][key]
 	if !ok {
 		return "", fmt.Errorf("unknown key '%s'", key)
 	}
 	return r, nil
 }
 
 // Reset implements the Memory interface.
 func(ca *Cache) Reset() {
 	var v string
 	if len(ca.Cache) == 0 {
 		return
 	}
 	ca.Cache = ca.Cache[:1]
 	ca.CacheUseSize = 0
 	for _, v = range ca.Cache[0] {
 		ca.CacheUseSize += uint32(len(v))
 	}
 	return
 }
 
 // Push implements the Memory interface.
 func (ca *Cache) Push() error {
 	m := make(map[string]string)
 	ca.Cache = append(ca.Cache, m)
 	return nil
 }
 
 // Pop implements the Memory interface.
 func (ca *Cache) Pop() error {
 	l := len(ca.Cache)
 	if l == 0 {
 		return fmt.Errorf("already at top level")
 	}
 	l -= 1
 	m := ca.Cache[l]
 	for k, v := range m {
 		sz := len(v)
 		ca.CacheUseSize -= uint32(sz)
 		delete(ca.Sizes, k)
 		logg.Debugf("Cache free", "frame", l, "key", k, "size", sz)
 	}
 	ca.Cache = ca.Cache[:l]
 	if l == 0 {
 		ca.Push()
 	}
 	return nil
 }
 
 // Check returns true if a key already exists in the cache.
 func(ca *Cache) Check(key string) bool {
 	return ca.frameOf(key) == -1
 }
 
 // Last implements the Memory interface.
 //
 // TODO: needs to be invalidated when out of scope
 func(ca *Cache) Last() string {
 	s := ca.LastValue
 	ca.LastValue = ""
 	return s
 }
 
 // bytes that will be added to cache use size for string
 // returns 0 if capacity would be exceeded
 func(ca *Cache) checkCapacity(v string) uint32 {
 	sz := uint32(len(v))
 	if ca.CacheSize == 0 {
 		return sz
 	}
 	if ca.CacheUseSize + sz > ca.CacheSize {
 		return 0	
 	}
 	return sz
 }
 
 // return 0-indexed frame number where key is defined. -1 if not defined
 func(ca *Cache) frameOf(key string) int {
 	for i, m := range ca.Cache {
 		for k, _ := range m {
 			if k == key {
 				return i
 			}
 		}
 	}
 	return -1
 }
 
 // Levels implements the Memory interface.
 func(ca *Cache) Levels() uint32 {
 	return uint32(len(ca.Cache))
 }
 
 // Keys implements the Memory interface.
 func(ca *Cache) Keys(level uint32) []string {
 	var r []string
 	for k := range ca.Cache[level] {
 		r = append(r, k)
 	}
 	return r
 }