raft/storage.go
func (ms *MemoryStorage) Snapshot() (pb.Snapshot, error) {
	ms.Lock()
	defer ms.Unlock()
	return ms.snapshot, nil
}
func (ms *MemoryStorage) Snapshot() (pb.Snapshot, error) {
	ms.Lock()
	defer ms.Unlock()
	return ms.snapshot, nil
}
// Snapshot implements the Storage interface.