/* Entry point for un-sharing file with a user*/
        public void unShareFileWithUser(string clientId, string filename, string sharedWithUser)
        {
            Logger.Debug("Un Sharing file " + filename + " owned by user " + clientId + " with user " + sharedWithUser);
            UserFileSystem fs          = getUserFSFromMapSynchronized(clientId);
            bool           filepresent = fs.isFilePresentSynchronized(filename);

            fs.removeSharedUserFromFileSynchronized(filename, sharedWithUser);

            if (!filepresent)
            {
                throw new FileNotFoundException("File not present in memory for client : " + filename + " for client : " + clientId);
            }

            UserFileSystem sharedFS = getUserFSFromMapSynchronized(sharedWithUser);
            bool           deleted  = sharedFS.deleteSharedFileSynchronized(new SharedFile(clientId, filename));

            if (!deleted)
            {
                Logger.Debug("Shared file was not present , skipping deletion");
            }
        }