code: public File createTmpFileForWrite(String pathStr, long size, 
        Configuration conf) throws IOException {
      AllocatorPerContext context = obtainContext(contextCfgItemName);
      return context.createTmpFileForWrite(pathStr, size, conf);
    }
docs: Creates a temporary file in the local FS. Pass size as -1 if not known
  apriori. We round-robin over the set of disks (via the configured dirs)
  and select the first complete path which has enough space. A file is
  created on this directory. The file is guaranteed to go away when the
  JVM exits.
  @param pathStr prefix for the temporary file
  @param size the size of the file that is going to be written
  @param conf the Configuration object
  @return a unique temporary file
  @throws IOException