avoid data race of TraverseBfs (#3856)

* avoid data race of TraverseBfs

* close is enough
avoid panic
I1014 12:29:59.207120 volume_loading.go:131 loading sorted db /tmp/sw/test2_19.sdx error: unexpected file /tmp/sw/test2_19.idx size: 255
I1014 12:29:59.207125 volume_loading.go:119 open to write file /tmp/sw/test4_26.idx
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x5260a4c]

goroutine 287 [running]:
github.com/seaweedfs/seaweedfs/weed/storage.(*SortedFileNeedleMap).Close(0x0)
        /Users/tochka/GolandProjects/seaweedfs/weed/storage/needle_map_sorted_file.go:97 +0x2c
github.com/seaweedfs/seaweedfs/weed/storage.(*Volume).load.func1()
        /Users/tochka/GolandProjects/seaweedfs/weed/storage/volume_loading.go:32 +0x8e
github.com/seaweedfs/seaweedfs/weed/storage.(*Volume).load(0xc001b36280, 0x1, 0x1, 0x0, 0x69228c0?)
        /Users/tochka/GolandProjects/seaweedfs/weed/storage/volume_loading.go:205 +0x256c
github.com/seaweedfs/seaweedfs/weed/storage.NewVolume({0x7ffeefbff6e0, 0x7}, {0x7ffeefbff6e0, 0x7}, {0xc0009a9284, 0x5}, 0x13, 0x0, 0x0, 0x0, ...)
        /Users/tochka/GolandProjects/seaweedfs/weed/storage/volume.go:62 +0x30f
github.com/seaweedfs/seaweedfs/weed/storage.(*DiskLocation).loadExistingVolume(0xc0006f40c0, {0x846c8d0, 0xc0009ce600}, 0x0?, 0x1)
        /Users/tochka/GolandProjects/seaweedfs/weed/storage/disk_location.go:161 +0x4da
github.com/seaweedfs/seaweedfs/weed/storage.(*DiskLocation).concurrentLoadingVolumes.func2()
        /Users/tochka/GolandProjects/seaweedfs/weed/storage/disk_location.go:201 +0xf9
created by github.com/seaweedfs/seaweedfs/weed/storage.(*DiskLocation).concurrentLoadingVolumes
        /Users/tochka/GolandProjects/seaweedfs/weed/storage/disk_location.go:198 +0x150

2 files changed, 25 insertions, 18 deletions

diff --git a/weed/pb/filer_pb/filer_client_bfs.go b/weed/pb/filer_pb/filer_client_bfs.go
index 6ae4a50cf..cb9367a7d 100644
--- a/weed/pb/filer_pb/filer_client_bfs.go
+++ b/weed/pb/filer_pb/filer_client_bfs.go
@@ -9,37 +9,41 @@ import (
 )
 
 func TraverseBfs(filerClient FilerClient, parentPath util.FullPath, fn func(parentPath util.FullPath, entry *Entry)) (err error) {
-
 	K := 5
 
 	var jobQueueWg sync.WaitGroup
 	queue := util.NewQueue()
 	jobQueueWg.Add(1)
 	queue.Enqueue(parentPath)
-	var isTerminating bool
+	terminates := make([]chan bool, K)
 
 	for i := 0; i < K; i++ {
-		go func() {
+		terminates[i] = make(chan bool)
+		go func(j int) {
 			for {
-				if isTerminating {
-					break
-				}
-				t := queue.Dequeue()
-				if t == nil {
-					time.Sleep(329 * time.Millisecond)
-					continue
-				}
-				dir := t.(util.FullPath)
-				processErr := processOneDirectory(filerClient, dir, queue, &jobQueueWg, fn)
-				if processErr != nil {
-					err = processErr
+				select {
+				case <-terminates[j]:
+					return
+				default:
+					t := queue.Dequeue()
+					if t == nil {
+						time.Sleep(329 * time.Millisecond)
+						continue
+					}
+					dir := t.(util.FullPath)
+					processErr := processOneDirectory(filerClient, dir, queue, &jobQueueWg, fn)
+					if processErr != nil {
+						err = processErr
+					}
+					jobQueueWg.Done()
 				}
-				jobQueueWg.Done()
 			}
-		}()
+		}(i)
 	}
 	jobQueueWg.Wait()
-	isTerminating = true
+	for i := 0; i < K; i++ {
+		close(terminates[i])
+	}
 	return
 }
 
diff --git a/weed/storage/needle_map_sorted_file.go b/weed/storage/needle_map_sorted_file.go
index c610f0d20..977237f85 100644
--- a/weed/storage/needle_map_sorted_file.go
+++ b/weed/storage/needle_map_sorted_file.go
@@ -94,6 +94,9 @@ func (m *SortedFileNeedleMap) Delete(key NeedleId, offset Offset) error {
 }
 
 func (m *SortedFileNeedleMap) Close() {
+	if m == nil {
+		return
+	}
 	if m.indexFile != nil {
 		m.indexFile.Close()
 	}