[#536] blobovnicza: Add blobovniczatree DB cache

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/local_object_storage/blobstor/blobovniczatree/cache.go

@@ -0,0 +1,103 @@
+package blobovniczatree
+
+import (
+	"fmt"
+	"sync"
+
+	utilSync "git.frostfs.info/TrueCloudLab/frostfs-node/pkg/util/sync"
+	"github.com/hashicorp/golang-lru/v2/simplelru"
+)
+
+// dbCache caches sharedDB instances that are NOT open for Put.
+//
+// Uses dbManager for opening/closing sharedDB instances.
+// Stores a reference to an cached sharedDB, so dbManager does not close it.
+type dbCache struct {
+	cacheGuard *sync.RWMutex
+	cache      simplelru.LRUCache[string, *sharedDB]
+	pathLock   *utilSync.KeyLocker[string]
+	closed     bool
+
+	dbManager *dbManager
+}
+
+func newDBCache(size int, dbManager *dbManager) *dbCache {
+	cache, err := simplelru.NewLRU[string, *sharedDB](size, func(_ string, evictedDB *sharedDB) {
+		evictedDB.Close()
+	})
+	if err != nil {
+		// occurs only if the size is not positive
+		panic(fmt.Errorf("could not create LRU cache of size %d: %w", size, err))
+	}
+	return &dbCache{
+		cacheGuard: &sync.RWMutex{},
+		cache:      cache,
+		dbManager:  dbManager,
+		pathLock:   utilSync.NewKeyLocker[string](),
+	}
+}
+
+func (c *dbCache) Open() {
+	c.cacheGuard.Lock()
+	defer c.cacheGuard.Unlock()
+
+	c.closed = false
+}
+
+func (c *dbCache) Close() {
+	c.cacheGuard.Lock()
+	defer c.cacheGuard.Unlock()
+	c.cache.Purge()
+	c.closed = true
+}
+
+func (c *dbCache) GetOrCreate(path string) *sharedDB {
+	value := c.getExisted(path)
+	if value != nil {
+		return value
+	}
+	return c.create(path)
+}
+
+func (c *dbCache) getExisted(path string) *sharedDB {
+	c.cacheGuard.Lock()
+	defer c.cacheGuard.Unlock()
+
+	if value, ok := c.cache.Get(path); ok {
+		return value
+	}
+	return nil
+}
+
+func (c *dbCache) create(path string) *sharedDB {
+	c.pathLock.Lock(path)
+	defer c.pathLock.Unlock(path)
+
+	value := c.getExisted(path)
+	if value != nil {
+		return value
+	}
+
+	value = c.dbManager.GetByPath(path)
+
+	_, err := value.Open() //open db to hold reference, closed by evictedDB.Close() or if cache closed
+	if err != nil {
+		return value
+	}
+	if added := c.put(path, value); !added {
+		value.Close()
+	}
+	return value
+}
+
+func (c *dbCache) put(path string, db *sharedDB) bool {
+	c.cacheGuard.Lock()
+	defer c.cacheGuard.Unlock()
+
+	if !c.closed {
+		c.cache.Add(path, db)
+		return true
+	}
+
+	return false
+}