Merge pull request #1 from MichailKon/lib

Add size cache

Author: misha567889

.gitignore

@@ -0,0 +1 @@
+.idea

db/db.go

@@ -4,7 +4,7 @@ import (
 	"gorm.io/driver/postgres"
 	"gorm.io/gorm"
 	"log/slog"
-	"main/db/models"
+	"testing_system/db/models"
 )
 
 func NewDb(config Config) (*gorm.DB, error) {

go.mod

@@ -1,4 +1,4 @@
-module main
+module testing_system
 
 go 1.22
 

lib/cache/cache.go

@@ -0,0 +1,233 @@
+package cache
+
+import (
+	"container/list"
+	"sync"
+	"testing_system/lib/logger"
+)
+
+type valHolder[TValue any] struct {
+	Value *TValue
+	Error error
+
+	LockCount     uint64
+	Size          uint64
+	LoadingStatus *sync.WaitGroup
+	ListPosition  *list.Element
+}
+
+// LRUSizeCache is simple key value LRU cache that accepts size bound for values
+// Cache has Getter and may have Remover functions
+// Cache removes the least recently used value if the total size bound is exceeded
+//
+// Getter will be called to get value for specified key
+// If value can be loaded, getter must return value, and size of value
+// If value can not be loaded, getter must return error and size of value (even with error)
+//
+// # If Remover is specified, and item has been loaded without error, Remover will be called before value removal
+//
+// Lock and Unlock methods can be used to avoid removal of specific keys
+type LRUSizeCache[TKey comparable, TValue any] struct {
+	mutex        sync.Mutex
+	valueHolders map[TKey]*valHolder[TValue]
+
+	getter  func(TKey) (*TValue, error, uint64)
+	remover func(TKey, *TValue)
+
+	sizeBound uint64
+	totalSize uint64
+
+	recentRank *list.List
+}
+
+// NewLRUSizeCache creates new cache for given size bound
+func NewLRUSizeCache[TKey comparable, TValue any](
+	sizeBound uint64,
+	getter func(TKey) (*TValue, error, uint64),
+	remover func(TKey, *TValue),
+) *LRUSizeCache[TKey, TValue] {
+	return &LRUSizeCache[TKey, TValue]{
+		valueHolders: make(map[TKey]*valHolder[TValue]),
+
+		getter:  getter,
+		remover: remover,
+
+		sizeBound: sizeBound,
+		totalSize: 0,
+
+		recentRank: list.New(),
+	}
+}
+
+// Get returns item from cache.
+//
+// If id is not found, it will be loaded and get method will wait until value is loaded.
+// If loader returned error, this error will be returned along with item
+func (c *LRUSizeCache[TKey, TValue]) Get(key TKey) (*TValue, error) {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+
+	valueHolder := c.lockAndGetHolder(key)
+	if valueHolder.LoadingStatus == nil {
+		valueHolder.LockCount--
+		c.itemUsed(key, valueHolder)
+		return valueHolder.Value, valueHolder.Error
+	}
+
+	loadingStatus := valueHolder.LoadingStatus
+	c.mutex.Unlock()
+
+	loadingStatus.Wait()
+	c.mutex.Lock()
+
+	// Lock count is increased, so value can not be removed
+	valueHolder = c.valueHolders[key]
+	valueHolder.LockCount--
+	c.itemUsed(key, valueHolder)
+	// Mutex is deferred at the beginning
+	return valueHolder.Value, valueHolder.Error
+}
+
+// Lock locks item in cache to avoid its removal.
+//
+// If element is not present in cache, it will start loading in background
+// Multiple lock can be added to item, they will require multiple unlock calls
+func (c *LRUSizeCache[TKey, TValue]) Lock(key TKey) {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+	valueHolder := c.lockAndGetHolder(key)
+	if valueHolder.LoadingStatus == nil {
+		c.itemUsed(key, valueHolder) // Only loaded items can appear in RankList
+	}
+}
+
+// Unlock unlocks item in cache so that it can be removed.
+//
+// If item is not found, ErrItemNotFound will be returned
+// If item is not locked, ErrNotLocked will be returned
+func (c *LRUSizeCache[TKey, TValue]) Unlock(key TKey) error {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+
+	valueHolder, ok := c.valueHolders[key]
+	if ok {
+		if valueHolder.LockCount > 0 {
+			valueHolder.LockCount--
+		} else {
+			return &ErrItemNotLocked{key: key}
+		}
+		c.removeItemsIfNeeded()
+		return nil
+	} else {
+		return &ErrItemNotFound{key: key}
+	}
+}
+
+// Remove removes item from cache.
+//
+// If item does not exist in cache, returns nil.
+// If item is locked, returns ErrItemLocked.
+func (c *LRUSizeCache[TKey, TValue]) Remove(key TKey) error {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+
+	valueHolder, ok := c.valueHolders[key]
+	if !ok {
+		return nil
+	}
+
+	if valueHolder.LockCount > 0 {
+		return &ErrItemLocked{key: key}
+	}
+
+	c.removeSingleItem(key)
+	return nil
+}
+
+// Mutex must be locked
+// Increases lock count
+// If value is loaded, returns valueHolder
+// If value is loading, returns valueHolder with active waitgroup
+// If value is absent, starts loading in background and returns valueHolder with active waitgroup
+func (c *LRUSizeCache[TKey, TValue]) lockAndGetHolder(key TKey) *valHolder[TValue] {
+	valueHolder, ok := c.valueHolders[key]
+	if ok {
+		valueHolder.LockCount++
+		return valueHolder
+	}
+	valueHolder = &valHolder[TValue]{
+		LoadingStatus: &sync.WaitGroup{},
+		LockCount:     1,
+	}
+
+	valueHolder.LoadingStatus.Add(1)
+	c.valueHolders[key] = valueHolder
+
+	go c.loadAbsentValue(key)
+
+	return valueHolder
+}
+
+// Mutex must not be locked or this should be called in different goroutine
+// Value must be absent and no concurrent load for same key must be present
+func (c *LRUSizeCache[TKey, TValue]) loadAbsentValue(key TKey) {
+	value, err, size := c.getter(key)
+
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+	valueHolder := c.valueHolders[key]
+
+	if valueHolder.Value != nil || valueHolder.Error != nil {
+		logger.Panic("Error in LRUSizeCache. loadAbsentValue is called for already loaded key, key: %v", key)
+	}
+
+	valueHolder.Value = value
+	valueHolder.Error = err
+
+	c.totalSize += size
+	valueHolder.Size = size
+	valueHolder.LoadingStatus.Done()
+	valueHolder.LoadingStatus = nil // It will stay in other pointers
+
+	c.itemUsed(key, valueHolder)
+	c.removeItemsIfNeeded()
+}
+
+// Mutex must be locked
+func (c *LRUSizeCache[TKey, TValue]) itemUsed(key TKey, valueHolder *valHolder[TValue]) {
+	if valueHolder.ListPosition != nil {
+		c.recentRank.MoveToBack(valueHolder.ListPosition)
+	} else {
+		valueHolder.ListPosition = c.recentRank.PushBack(key)
+	}
+}
+
+// Mutex must be locked
+func (c *LRUSizeCache[TKey, TValue]) removeItemsIfNeeded() {
+	elem := c.recentRank.Front()
+	for c.totalSize > c.sizeBound && elem != nil {
+		key := elem.Value.(TKey)
+		valueHolder := c.valueHolders[key]
+		elem = elem.Next()
+
+		if valueHolder.LockCount == 0 {
+			c.removeSingleItem(key)
+		}
+	}
+}
+
+// Mutex must be locked
+// Key, Value must be present and lock count should be zero
+func (c *LRUSizeCache[TKey, TValue]) removeSingleItem(key TKey) {
+	valueHolder := c.valueHolders[key]
+	if valueHolder.LockCount != 0 {
+		logger.Panic("Error in LRUSizeCache. Removing key with non zero lock count, key: %#v", key)
+	}
+	if c.remover != nil && valueHolder.Error != nil {
+		c.remover(key, valueHolder.Value)
+	}
+
+	delete(c.valueHolders, key)
+	c.totalSize -= valueHolder.Size
+	c.recentRank.Remove(valueHolder.ListPosition)
+}

lib/cache/errors.go

@@ -0,0 +1,27 @@
+package cache
+
+import "fmt"
+
+type ErrItemLocked struct {
+	key interface{}
+}
+
+func (e *ErrItemLocked) Error() string {
+	return fmt.Sprintf("size_cache: item is locked, key: %#v", e.key)
+}
+
+type ErrItemNotFound struct {
+	key interface{}
+}
+
+func (e *ErrItemNotFound) Error() string {
+	return fmt.Sprintf("size_cache: item not found, key: %#v", e.key)
+}
+
+type ErrItemNotLocked struct {
+	key interface{}
+}
+
+func (e *ErrItemNotLocked) Error() string {
+	return fmt.Sprintf("size_cache: item not locked, key: %#v", e.key)
+}

lib/logger/logger.go

@@ -0,0 +1,5 @@
+package logger
+
+func Panic(format string, v ...interface{}) {
+	// TODO: create logger
+}