Javadoc
This will free sockets and file descriptors held by the stream only when the stream implements
org.apache.hadoop.fs.CanUnbuffer. NOT THREAD SAFE. Must be called only when all the clients
using this stream to read the blocks have finished reading. If by chance the stream is
unbuffered and there are clients still holding this stream for read then on next client read
request a new socket will be opened by Datanode without client knowing about it and will serve
its read request. Note: If this socket is idle for some time then the DataNode will close the
socket and the socket will move into CLOSE_WAIT state and on the next client request on this
stream, the current socket will be closed and a new socket will be opened to serve the
requests.