code: protected void setLength(long length) throws IOException {
  		if(length<0) throw new IllegalArgumentException("Invalid length: "+length);
  		synchronized(this) {
  			file.seek(8);
  			file.writeLong(length);
  			if(length==0) setFirstIndex(0);
  		}
  	}
docs: Sets the number of bytes currently contained by the FIFO.