rclone/lib/cache/cache.go
2021-03-15 19:22:07 +00:00

204 lines
4.9 KiB
Go

// Package cache implements a simple cache where the entries are
// expired after a given time (5 minutes of disuse by default).
package cache
import (
"strings"
"sync"
"time"
)
// Cache holds values indexed by string, but expired after a given (5
// minutes by default).
type Cache struct {
mu sync.Mutex
cache map[string]*cacheEntry
expireRunning bool
expireDuration time.Duration // expire the cache entry when it is older than this
expireInterval time.Duration // interval to run the cache expire
}
// New creates a new cache with the default expire duration and interval
func New() *Cache {
return &Cache{
cache: map[string]*cacheEntry{},
expireRunning: false,
expireDuration: 300 * time.Second,
expireInterval: 60 * time.Second,
}
}
// cacheEntry is stored in the cache
type cacheEntry struct {
value interface{} // cached item
err error // creation error
key string // key
lastUsed time.Time // time used for expiry
pinCount int // non zero if the entry should not be removed
}
// CreateFunc is called to create new values. If the create function
// returns an error it will be cached if ok is true, otherwise the
// error will just be returned, allowing negative caching if required.
type CreateFunc func(key string) (value interface{}, ok bool, error error)
// used marks an entry as accessed now and kicks the expire timer off
// should be called with the lock held
func (c *Cache) used(entry *cacheEntry) {
entry.lastUsed = time.Now()
if !c.expireRunning {
time.AfterFunc(c.expireInterval, c.cacheExpire)
c.expireRunning = true
}
}
// Get gets a value named key either from the cache or creates it
// afresh with the create function.
func (c *Cache) Get(key string, create CreateFunc) (value interface{}, err error) {
c.mu.Lock()
entry, ok := c.cache[key]
if !ok {
c.mu.Unlock() // Unlock in case Get is called recursively
value, ok, err = create(key)
if err != nil && !ok {
return value, err
}
entry = &cacheEntry{
value: value,
key: key,
err: err,
}
c.mu.Lock()
c.cache[key] = entry
}
defer c.mu.Unlock()
c.used(entry)
return entry.value, entry.err
}
func (c *Cache) addPin(key string, count int) {
c.mu.Lock()
entry, ok := c.cache[key]
if ok {
entry.pinCount += count
c.used(entry)
}
c.mu.Unlock()
}
// Pin a value in the cache if it exists
func (c *Cache) Pin(key string) {
c.addPin(key, 1)
}
// Unpin a value in the cache if it exists
func (c *Cache) Unpin(key string) {
c.addPin(key, -1)
}
// Put puts a value named key into the cache
func (c *Cache) Put(key string, value interface{}) {
c.mu.Lock()
defer c.mu.Unlock()
entry := &cacheEntry{
value: value,
key: key,
}
c.used(entry)
c.cache[key] = entry
}
// GetMaybe returns the key and true if found, nil and false if not
func (c *Cache) GetMaybe(key string) (value interface{}, found bool) {
c.mu.Lock()
defer c.mu.Unlock()
entry, found := c.cache[key]
if !found {
return nil, found
}
c.used(entry)
return entry.value, found
}
// Delete the entry passed in
//
// Returns true if the entry was found
func (c *Cache) Delete(key string) bool {
c.mu.Lock()
_, found := c.cache[key]
delete(c.cache, key)
c.mu.Unlock()
return found
}
// DeletePrefix deletes all entries with the given prefix
//
// Returns number of entries deleted
func (c *Cache) DeletePrefix(prefix string) (deleted int) {
c.mu.Lock()
for k := range c.cache {
if strings.HasPrefix(k, prefix) {
delete(c.cache, k)
deleted++
}
}
c.mu.Unlock()
return deleted
}
// Rename renames the item at oldKey to newKey.
//
// If there was an existing item at newKey then it takes precedence
// and is returned otherwise the item (if any) at oldKey is returned.
func (c *Cache) Rename(oldKey, newKey string) (value interface{}, found bool) {
c.mu.Lock()
if newEntry, newFound := c.cache[newKey]; newFound {
// If new entry is found use that
delete(c.cache, oldKey)
value, found = newEntry.value, newFound
c.used(newEntry)
} else if oldEntry, oldFound := c.cache[oldKey]; oldFound {
// If old entry is found rename it to new and use that
c.cache[newKey] = oldEntry
delete(c.cache, oldKey)
c.used(oldEntry)
value, found = oldEntry.value, oldFound
}
c.mu.Unlock()
return value, found
}
// cacheExpire expires any entries that haven't been used recently
func (c *Cache) cacheExpire() {
c.mu.Lock()
defer c.mu.Unlock()
now := time.Now()
for key, entry := range c.cache {
if entry.pinCount <= 0 && now.Sub(entry.lastUsed) > c.expireDuration {
delete(c.cache, key)
}
}
if len(c.cache) != 0 {
time.AfterFunc(c.expireInterval, c.cacheExpire)
c.expireRunning = true
} else {
c.expireRunning = false
}
}
// Clear removes everything from the cache
func (c *Cache) Clear() {
c.mu.Lock()
for k := range c.cache {
delete(c.cache, k)
}
c.mu.Unlock()
}
// Entries returns the number of entries in the cache
func (c *Cache) Entries() int {
c.mu.Lock()
entries := len(c.cache)
c.mu.Unlock()
return entries
}