fix(joiner): resolve race condition

Author: gacevicljubisa

pkg/file/joiner/joiner.go

@@ -81,6 +81,14 @@ func (g *decoderCache) createRemoveCallback(key string) func(error) {
 	}
 }
 
+// getFromCache safely retrieves a decoder from cache with lock
+func (g *decoderCache) getFromCache(key string) (storage.Getter, bool) {
+	g.mu.Lock()
+	defer g.mu.Unlock()
+	d, ok := g.cache[key]
+	return d, ok
+}
+
 // GetOrCreate returns a decoder for the given chunk address
 func (g *decoderCache) GetOrCreate(addrs []swarm.Address, shardCnt int) storage.Getter {
 	// since a recovery decoder is not allowed, simply return the underlying netstore
@@ -93,9 +101,8 @@ func (g *decoderCache) GetOrCreate(addrs []swarm.Address, shardCnt int) storage.
 	}
 
 	key := fingerprint(addrs)
-	g.mu.Lock()
-	defer g.mu.Unlock()
-	d, ok := g.cache[key]
+	d, ok := g.getFromCache(key)
+
 	if ok {
 		if d == nil {
 			// The nil value indicates a previous successful recovery
@@ -105,15 +112,20 @@ func (g *decoderCache) GetOrCreate(addrs []swarm.Address, shardCnt int) storage.
 			// Create a factory function that will instantiate the decoder only when needed
 			recovery := func() storage.Getter {
 				g.config.Logger.Debug("lazy-creating recovery decoder after fetch failed", "key", key)
+
+				if d, ok := g.getFromCache(key); ok && d != nil {
+					return d
+				}
+
+				newGetter := getter.New(addrs, shardCnt, g.fetcher, g.putter, decoderCallback, g.config)
+
 				g.mu.Lock()
 				defer g.mu.Unlock()
-				d, ok := g.cache[key]
-				if ok && d != nil {
+				if d, ok := g.cache[key]; ok && d != nil {
 					return d
 				}
-				d = getter.New(addrs, shardCnt, g.fetcher, g.putter, decoderCallback, g.config)
-				g.cache[key] = d
-				return d
+				g.cache[key] = newGetter
+				return newGetter
 			}
 
 			return getter.NewReDecoder(g.fetcher, recovery, g.config.Logger)
@@ -122,9 +134,16 @@ func (g *decoderCache) GetOrCreate(addrs []swarm.Address, shardCnt int) storage.
 	}
 
 	removeCallback := g.createRemoveCallback(key)
-	d = getter.New(addrs, shardCnt, g.fetcher, g.putter, removeCallback, g.config)
-	g.cache[key] = d
-	return d
+	newGetter := getter.New(addrs, shardCnt, g.fetcher, g.putter, removeCallback, g.config)
+
+	// ensure no other goroutine created the same getter
+	g.mu.Lock()
+	defer g.mu.Unlock()
+	if d, ok := g.cache[key]; ok {
+		return d
+	}
+	g.cache[key] = newGetter
+	return newGetter
 }
 
 // New creates a new Joiner. A Joiner provides Read, Seek and Size functionalities.