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