lib/persistentqueue: protect from multiple concurrent opening for the same persistent queue

lib/persistentqueue/persistentqueue.go

@@ -35,6 +35,8 @@ type Queue struct {
 	dir  string
 	name string
 
+	flockF *os.File
+
 	// mu protects all the fields below.
 	mu sync.Mutex
 
@@ -156,7 +158,16 @@ func mustOpen(path, name string, chunkFileSize, maxBlockSize, maxPendingBytes ui
 	return q
 }
 
+func mustCreateFlockFile(path string) *os.File {
+	f, err := fs.CreateFlockFile(path)
+	if err != nil {
+		logger.Panicf("FATAL: %s", err)
+	}
+	return f
+}
+
 func tryOpeningQueue(path, name string, chunkFileSize, maxBlockSize, maxPendingBytes uint64) (*Queue, error) {
+	// Protect from concurrent opens.
 	var q Queue
 	q.chunkFileSize = chunkFileSize
 	q.maxBlockSize = maxBlockSize
@@ -187,6 +198,13 @@ func tryOpeningQueue(path, name string, chunkFileSize, maxBlockSize, maxPendingB
 	if err := fs.MkdirAllIfNotExist(path); err != nil {
 		return nil, fmt.Errorf("cannot create directory %q: %w", path, err)
 	}
+	q.flockF = mustCreateFlockFile(path)
+	mustCloseFlockF := true
+	defer func() {
+		if mustCloseFlockF {
+			_ = q.flockF.Close()
+		}
+	}()
 
 	// Read metainfo.
 	var mi metainfo
@@ -230,6 +248,10 @@ func tryOpeningQueue(path, name string, chunkFileSize, maxBlockSize, maxPendingB
 			// skip metainfo file
 			continue
 		}
+		if fname == "flock.lock" {
+			// skip flock file
+			continue
+		}
 		if !chunkFileNameRegex.MatchString(fname) {
 			logger.Errorf("skipping unknown file %q", filepath)
 			continue
@@ -314,6 +336,7 @@ func tryOpeningQueue(path, name string, chunkFileSize, maxBlockSize, maxPendingB
 		cleanOnError()
 		return nil, fmt.Errorf("couldn't find chunk file for writing in %q", q.dir)
 	}
+	mustCloseFlockF = false
 	return &q, nil
 }
 
@@ -342,6 +365,12 @@ func (q *Queue) MustClose() {
 	if err := q.flushMetainfoLocked(); err != nil {
 		logger.Panicf("FATAL: cannot flush chunked queue metainfo: %s", err)
 	}
+
+	// Close flockF
+	if err := q.flockF.Close(); err != nil {
+		logger.Panicf("FATAL: cannot close flock file: %s", err)
+	}
+	q.flockF = nil
 }
 
 func (q *Queue) chunkFilePath(offset uint64) string {