block read might miss some data

hi bfs,
I'm reading your chunk server code,and the code in the Block::Read seems might miss some data already written.Now the read data process is:
diskfile --> block_buf_list_ --> block buf

However,I think that while someone doing read,someone can write,the writer might add data into "recv_window_".So the correct way i think is:
diskfile --> block_buf_list --> recv_windows_ --> block buf

Through,as the write and read might happen concurrently,the data might be mixed.Is that right?

Start in the chunk server's Block::Read entry point and trace the path from diskfile through block_buf_list_ to the block buffer. Compare that path with writes entering recv_window_ while a read is in progress, and determine whether concurrent operations can omit or mix data; done means the behavior is confirmed and the required read/write handling is clearly defined.

Written by the indexing model from the issue text.