gatus/vendor/github.com/TwinProduction/gocache/gocache.go

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package gocache
import (
"errors"
"reflect"
"sync"
"time"
)
var (
Debug = false
)
const (
// NoMaxSize means that the cache has no maximum number of entries in the cache
// Setting Cache.maxSize to this value also means there will be no eviction
NoMaxSize = 0
// NoMaxMemoryUsage means that the cache has no maximum number of entries in the cache
NoMaxMemoryUsage = 0
// DefaultMaxSize is the max size set if no max size is specified
DefaultMaxSize = 100000
// NoExpiration is the value that must be used as TTL to specify that the given key should never expire
NoExpiration = -1
Kilobyte = 1024
Megabyte = 1024 * Kilobyte
Gigabyte = 1024 * Megabyte
)
var (
ErrKeyDoesNotExist = errors.New("key does not exist")
ErrKeyHasNoExpiration = errors.New("key has no expiration")
ErrJanitorAlreadyRunning = errors.New("janitor is already running")
)
// Cache is the core struct of gocache which contains the data as well as all relevant configuration fields
type Cache struct {
// maxSize is the maximum amount of entries that can be in the cache at any given time
// By default, this is set to DefaultMaxSize
maxSize int
// maxMemoryUsage is the maximum amount of memory that can be taken up by the cache at any time
// By default, this is set to NoMaxMemoryUsage, meaning that the default behavior is to not evict
// based on maximum memory usage
maxMemoryUsage int
// evictionPolicy is the eviction policy
evictionPolicy EvictionPolicy
// stats is the object that contains cache statistics/metrics
stats *Statistics
// entries is the content of the cache
entries map[string]*Entry
// mutex is the lock for making concurrent operations on the cache
mutex sync.RWMutex
// head is the cache entry at the head of the cache
head *Entry
// tail is the last cache node and also the next entry that will be evicted
tail *Entry
// stopJanitor is the channel used to stop the janitor
stopJanitor chan bool
// memoryUsage is the approximate memory usage of the cache (dataset only) in bytes
memoryUsage int
// forceNilInterfaceOnNilPointer determines whether all Set-like functions should set a value as nil if the
// interface passed has a nil value but not a nil type.
//
// By default, interfaces are only nil when both their type and value is nil.
// This means that when you pass a pointer to a nil value, the type of the interface
// will still show as nil, which means that if you don't cast the interface after
// retrieving it, a nil check will return that the value is not false.
forceNilInterfaceOnNilPointer bool
}
// MaxSize returns the maximum amount of keys that can be present in the cache before
// new entries trigger the eviction of the tail
func (cache *Cache) MaxSize() int {
return cache.maxSize
}
// MaxMemoryUsage returns the configured maxMemoryUsage of the cache
func (cache *Cache) MaxMemoryUsage() int {
return cache.maxMemoryUsage
}
// EvictionPolicy returns the EvictionPolicy of the Cache
func (cache *Cache) EvictionPolicy() EvictionPolicy {
return cache.evictionPolicy
}
// Stats returns statistics from the cache
func (cache *Cache) Stats() Statistics {
cache.mutex.RLock()
stats := Statistics{
EvictedKeys: cache.stats.EvictedKeys,
ExpiredKeys: cache.stats.ExpiredKeys,
Hits: cache.stats.Hits,
Misses: cache.stats.Misses,
}
cache.mutex.RUnlock()
return stats
}
// MemoryUsage returns the current memory usage of the cache's dataset in bytes
// If MaxMemoryUsage is set to NoMaxMemoryUsage, this will return 0
func (cache *Cache) MemoryUsage() int {
return cache.memoryUsage
}
// WithMaxSize sets the maximum amount of entries that can be in the cache at any given time
// A maxSize of 0 or less means infinite
func (cache *Cache) WithMaxSize(maxSize int) *Cache {
if maxSize < 0 {
maxSize = NoMaxSize
}
if maxSize != NoMaxSize && cache.Count() == 0 {
cache.entries = make(map[string]*Entry, maxSize)
}
cache.maxSize = maxSize
return cache
}
// WithMaxMemoryUsage sets the maximum amount of memory that can be used by the cache at any given time
//
// NOTE: This is approximate.
//
// Setting this to NoMaxMemoryUsage will disable eviction by memory usage
func (cache *Cache) WithMaxMemoryUsage(maxMemoryUsageInBytes int) *Cache {
if maxMemoryUsageInBytes < 0 {
maxMemoryUsageInBytes = NoMaxMemoryUsage
}
cache.maxMemoryUsage = maxMemoryUsageInBytes
return cache
}
// WithEvictionPolicy sets eviction algorithm.
// Defaults to FirstInFirstOut (FIFO)
func (cache *Cache) WithEvictionPolicy(policy EvictionPolicy) *Cache {
cache.evictionPolicy = policy
return cache
}
// WithForceNilInterfaceOnNilPointer sets whether all Set-like functions should set a value as nil if the
// interface passed has a nil value but not a nil type.
//
// In Go, an interface is only nil if both its type and value are nil, which means that a nil pointer
// (e.g. (*Struct)(nil)) will retain its attribution to the type, and the unmodified value returned from
// Cache.Get, for instance, would return false when compared with nil if this option is set to false.
//
// We can bypass this by detecting if the interface's value is nil and setting it to nil rather than
// a nil pointer, which will make the value returned from Cache.Get return true when compared with nil.
// This is exactly what passing true to WithForceNilInterfaceOnNilPointer does, and it's also the default behavior.
//
// Alternatively, you may pass false to WithForceNilInterfaceOnNilPointer, which will mean that you'll have
// to cast the value returned from Cache.Get to its original type to check for whether the pointer returned
// is nil or not.
//
// If set to true:
// cache := gocache.NewCache().WithForceNilInterfaceOnNilPointer(true)
// cache.Set("key", (*Struct)(nil))
// value, _ := cache.Get("key")
// // the following returns true, because the interface{} was forcefully set to nil
// if value == nil {}
// // the following will panic, because the value has been casted to its type
// if value.(*Struct) == nil {}
//
// If set to false:
// cache := gocache.NewCache().WithForceNilInterfaceOnNilPointer(false)
// cache.Set("key", (*Struct)(nil))
// value, _ := cache.Get("key")
// // the following returns false, because the interface{} returned has a non-nil type (*Struct)
// if value == nil {}
// // the following returns true, because the value has been casted to its type
// if value.(*Struct) == nil {}
//
// In other words, if set to true, you do not need to cast the value returned from the cache to
// to check if the value is nil.
//
// Defaults to true
func (cache *Cache) WithForceNilInterfaceOnNilPointer(forceNilInterfaceOnNilPointer bool) *Cache {
cache.forceNilInterfaceOnNilPointer = forceNilInterfaceOnNilPointer
return cache
}
// NewCache creates a new Cache
//
// Should be used in conjunction with Cache.WithMaxSize, Cache.WithMaxMemoryUsage and/or Cache.WithEvictionPolicy
// gocache.NewCache().WithMaxSize(10000).WithEvictionPolicy(gocache.LeastRecentlyUsed)
//
func NewCache() *Cache {
return &Cache{
maxSize: DefaultMaxSize,
evictionPolicy: FirstInFirstOut,
stats: &Statistics{},
entries: make(map[string]*Entry),
mutex: sync.RWMutex{},
stopJanitor: nil,
forceNilInterfaceOnNilPointer: true,
}
}
// Set creates or updates a key with a given value
func (cache *Cache) Set(key string, value interface{}) {
cache.SetWithTTL(key, value, NoExpiration)
}
// SetWithTTL creates or updates a key with a given value and sets an expiration time (-1 is NoExpiration)
//
// The TTL provided must be greater than 0, or NoExpiration (-1). If a negative value that isn't -1 (NoExpiration) is
// provided, the entry will not be created if the key doesn't exist
func (cache *Cache) SetWithTTL(key string, value interface{}, ttl time.Duration) {
// An interface is only nil if both its value and its type are nil, however, passing a pointer
if cache.forceNilInterfaceOnNilPointer {
if value != nil && (reflect.ValueOf(value).Kind() == reflect.Ptr && reflect.ValueOf(value).IsNil()) {
value = nil
}
}
cache.mutex.Lock()
entry, ok := cache.get(key)
if !ok {
// A negative TTL that isn't -1 (NoExpiration) or 0 is an entry that will expire instantly,
// so might as well just not create it in the first place
if ttl != NoExpiration && ttl < 1 {
cache.mutex.Unlock()
return
}
// Cache entry doesn't exist, so we have to create a new one
entry = &Entry{
Key: key,
Value: value,
RelevantTimestamp: time.Now(),
previous: cache.head,
}
if cache.head == nil {
cache.tail = entry
} else {
cache.head.next = entry
}
cache.head = entry
cache.entries[key] = entry
if cache.maxMemoryUsage != NoMaxMemoryUsage {
cache.memoryUsage += entry.SizeInBytes()
}
} else {
// A negative TTL that isn't -1 (NoExpiration) or 0 is an entry that will expire instantly,
// so might as well just delete it immediately instead of updating it
if ttl != NoExpiration && ttl < 1 {
cache.delete(key)
cache.mutex.Unlock()
return
}
if cache.maxMemoryUsage != NoMaxMemoryUsage {
// Substract the old entry from the cache's memoryUsage
cache.memoryUsage -= entry.SizeInBytes()
}
// Update existing entry's value
entry.Value = value
entry.RelevantTimestamp = time.Now()
if cache.maxMemoryUsage != NoMaxMemoryUsage {
// Add the memory usage of the new entry to the cache's memoryUsage
cache.memoryUsage += entry.SizeInBytes()
}
// Because we just updated the entry, we need to move it back to HEAD
cache.moveExistingEntryToHead(entry)
}
if ttl != NoExpiration {
entry.Expiration = time.Now().Add(ttl).UnixNano()
} else {
entry.Expiration = NoExpiration
}
// If the cache doesn't have a maxSize/maxMemoryUsage, then there's no point checking if we need to evict
// an entry, so we'll just return now
if cache.maxSize == NoMaxSize && cache.maxMemoryUsage == NoMaxMemoryUsage {
cache.mutex.Unlock()
return
}
// If there's a maxSize and the cache has more entries than the maxSize, evict
if cache.maxSize != NoMaxSize && len(cache.entries) > cache.maxSize {
cache.evict()
}
// If there's a maxMemoryUsage and the memoryUsage is above the maxMemoryUsage, evict
if cache.maxMemoryUsage != NoMaxMemoryUsage && cache.memoryUsage > cache.maxMemoryUsage {
for cache.memoryUsage > cache.maxMemoryUsage && len(cache.entries) > 0 {
cache.evict()
}
}
cache.mutex.Unlock()
}
// SetAll creates or updates multiple values
func (cache *Cache) SetAll(entries map[string]interface{}) {
for key, value := range entries {
cache.SetWithTTL(key, value, NoExpiration)
}
}
// Get retrieves an entry using the key passed as parameter
// If there is no such entry, the value returned will be nil and the boolean will be false
// If there is an entry, the value returned will be the value cached and the boolean will be true
func (cache *Cache) Get(key string) (interface{}, bool) {
cache.mutex.Lock()
entry, ok := cache.get(key)
if !ok {
cache.mutex.Unlock()
cache.stats.Misses++
return nil, false
}
if entry.Expired() {
cache.stats.ExpiredKeys++
cache.delete(key)
cache.mutex.Unlock()
return nil, false
}
cache.stats.Hits++
if cache.evictionPolicy == LeastRecentlyUsed {
entry.Accessed()
if cache.head == entry {
cache.mutex.Unlock()
return entry.Value, true
}
// Because the eviction policy is LRU, we need to move the entry back to HEAD
cache.moveExistingEntryToHead(entry)
}
cache.mutex.Unlock()
return entry.Value, true
}
// GetByKeys retrieves multiple entries using the keys passed as parameter
// All keys are returned in the map, regardless of whether they exist or not, however, entries that do not exist in the
// cache will return nil, meaning that there is no way of determining whether a key genuinely has the value nil, or
// whether it doesn't exist in the cache using only this function.
func (cache *Cache) GetByKeys(keys []string) map[string]interface{} {
entries := make(map[string]interface{})
for _, key := range keys {
entries[key], _ = cache.Get(key)
}
return entries
}
// GetAll retrieves all cache entries
//
// If the eviction policy is LeastRecentlyUsed, note that unlike Get and GetByKeys, this does not update the last access
// timestamp. The reason for this is that since all cache entries will be accessed, updating the last access timestamp
// would provide very little benefit while harming the ability to accurately determine the next key that will be evicted
//
// You should probably avoid using this if you have a lot of entries.
//
// GetKeysByPattern is a good alternative if you want to retrieve entries that you do not have the key for, as it only
// retrieves the keys and does not trigger active eviction and has a parameter for setting a limit to the number of keys
// you wish to retrieve.
func (cache *Cache) GetAll() map[string]interface{} {
entries := make(map[string]interface{})
cache.mutex.Lock()
for key, entry := range cache.entries {
if entry.Expired() {
cache.delete(key)
continue
}
entries[key] = entry.Value
}
cache.stats.Hits += uint64(len(entries))
cache.mutex.Unlock()
return entries
}
// GetKeysByPattern retrieves a slice of keys that match a given pattern
// If the limit is set to 0, the entire cache will be searched for matching keys.
// If the limit is above 0, the search will stop once the specified number of matching keys have been found.
//
// e.g.
// cache.GetKeysByPattern("*some*", 0) will return all keys containing "some" in them
// cache.GetKeysByPattern("*some*", 5) will return 5 keys (or less) containing "some" in them
//
// Note that GetKeysByPattern does not trigger active evictions, nor does it count as accessing the entry, the latter
// only applying if the cache uses the LeastRecentlyUsed eviction policy.
// The reason for that behavior is that these two (active eviction and access) only applies when you access the value
// of the cache entry, and this function only returns the keys.
func (cache *Cache) GetKeysByPattern(pattern string, limit int) []string {
var matchingKeys []string
cache.mutex.Lock()
for key, value := range cache.entries {
if value.Expired() {
continue
}
if MatchPattern(pattern, key) {
matchingKeys = append(matchingKeys, key)
if limit > 0 && len(matchingKeys) >= limit {
break
}
}
}
cache.mutex.Unlock()
return matchingKeys
}
// Delete removes a key from the cache
//
// Returns false if the key did not exist.
func (cache *Cache) Delete(key string) bool {
cache.mutex.Lock()
ok := cache.delete(key)
cache.mutex.Unlock()
return ok
}
// DeleteAll deletes multiple entries based on the keys passed as parameter
//
// Returns the number of keys deleted
func (cache *Cache) DeleteAll(keys []string) int {
numberOfKeysDeleted := 0
cache.mutex.Lock()
for _, key := range keys {
if cache.delete(key) {
numberOfKeysDeleted++
}
}
cache.mutex.Unlock()
return numberOfKeysDeleted
}
// Count returns the total amount of entries in the cache, regardless of whether they're expired or not
func (cache *Cache) Count() int {
cache.mutex.RLock()
count := len(cache.entries)
cache.mutex.RUnlock()
return count
}
// Clear deletes all entries from the cache
func (cache *Cache) Clear() {
cache.mutex.Lock()
cache.entries = make(map[string]*Entry)
cache.memoryUsage = 0
cache.head = nil
cache.tail = nil
cache.mutex.Unlock()
}
// TTL returns the time until the cache entry specified by the key passed as parameter
// will be deleted.
func (cache *Cache) TTL(key string) (time.Duration, error) {
cache.mutex.RLock()
entry, ok := cache.get(key)
cache.mutex.RUnlock()
if !ok {
return 0, ErrKeyDoesNotExist
}
if entry.Expiration == NoExpiration {
return 0, ErrKeyHasNoExpiration
}
timeUntilExpiration := time.Until(time.Unix(0, entry.Expiration))
if timeUntilExpiration < 0 {
// The key has already expired but hasn't been deleted yet.
// From the client's perspective, this means that the cache entry doesn't exist
return 0, ErrKeyDoesNotExist
}
return timeUntilExpiration, nil
}
// Expire sets a key's expiration time
//
// A TTL of -1 means that the key will never expire
// A TTL of 0 means that the key will expire immediately
// If using LRU, note that this does not reset the position of the key
//
// Returns true if the cache key exists and has had its expiration time altered
func (cache *Cache) Expire(key string, ttl time.Duration) bool {
entry, ok := cache.get(key)
if !ok || entry.Expired() {
return false
}
if ttl != NoExpiration {
entry.Expiration = time.Now().Add(ttl).UnixNano()
} else {
entry.Expiration = NoExpiration
}
return true
}
// get retrieves an entry using the key passed as parameter, but unlike Get, it doesn't update the access time or
// move the position of the entry to the head
func (cache *Cache) get(key string) (*Entry, bool) {
entry, ok := cache.entries[key]
return entry, ok
}
func (cache *Cache) delete(key string) bool {
entry, ok := cache.entries[key]
if ok {
if cache.maxMemoryUsage != NoMaxMemoryUsage {
cache.memoryUsage -= entry.SizeInBytes()
}
cache.removeExistingEntryReferences(entry)
delete(cache.entries, key)
}
return ok
}
// moveExistingEntryToHead replaces the current cache head for an existing entry
func (cache *Cache) moveExistingEntryToHead(entry *Entry) {
if !(entry == cache.head && entry == cache.tail) {
cache.removeExistingEntryReferences(entry)
}
if entry != cache.head {
entry.previous = cache.head
entry.next = nil
if cache.head != nil {
cache.head.next = entry
}
cache.head = entry
}
}
// removeExistingEntryReferences modifies the next and previous reference of an existing entry and re-links
// the next and previous entry accordingly, as well as the cache head or/and the cache tail if necessary.
// Note that it does not remove the entry from the cache, only the references.
func (cache *Cache) removeExistingEntryReferences(entry *Entry) {
if cache.tail == entry && cache.head == entry {
cache.tail = nil
cache.head = nil
} else if cache.tail == entry {
cache.tail = cache.tail.next
} else if cache.head == entry {
cache.head = cache.head.previous
}
if entry.previous != nil {
entry.previous.next = entry.next
}
if entry.next != nil {
entry.next.previous = entry.previous
}
entry.next = nil
entry.previous = nil
}
// evict removes the tail from the cache
func (cache *Cache) evict() {
if cache.tail == nil || len(cache.entries) == 0 {
return
}
if cache.tail != nil {
oldTail := cache.tail
cache.removeExistingEntryReferences(oldTail)
delete(cache.entries, oldTail.Key)
if cache.maxMemoryUsage != NoMaxMemoryUsage {
cache.memoryUsage -= oldTail.SizeInBytes()
}
cache.stats.EvictedKeys++
}
}