append to swapfiles if they exist already

import scala.collection.mutable.ListBuffer

class SwapFile(metric_key: MetricKey) {

  var write_pos = 0

  val buffer = ByteBuffer.allocate(512)

  buffer.order(ByteOrder.BIG_ENDIAN)

  // each sample is 18 bytes big (2 bytes header, 8 bytes time and

  // 8 bytes value as double precision ieee 754 float)

  val file = new RandomAccessFile(new File(

    FnordMetric.CONFIG('swap_prefix), file_name), "rwd")

  val buffer = ByteBuffer.allocate(512)

  buffer.order(ByteOrder.BIG_ENDIAN)

  var write_pos = file.length.toInt

  println(write_pos)

  // adds a new (time, value) tuple to be written to the swap file

  // but does not write it yet. this method is not thread safe!

  def flush : Unit = {

    file.synchronized {

      file.seek(write_pos)

      file.write(buffer.array)

      file.write(buffer.array, 0, buffer.position)

    }

    write_pos += BLOCK_SIZE