/// <remarks>
/// Variables <code>head</code> and <code>tail</code> mark the start and
/// end of the messages received, but not delivered yet. When a message is
/// received, if its seqno is smaller than <code>head</code>, it is
/// discarded (already received). If it is bigger than <code>tail</code>,
/// we advance <code>tail</code> and add empty elements. If it is between
/// <code>head</code> and <code>tail</code>, we set the corresponding
/// missing (or already present) element. If it is equal to
/// <code>tail</code>, we advance the latter by 1 and add the message
/// (default case).
/// </remarks>
/// <summary>
/// Adds a message according to its sequence number.
/// </summary>
/// <param name="seqno">Sequence number of the message.</param>
/// <param name="msg">Message to add.</param>
public void add(long seqno, Message msg)
{
Entry current = null;
long old_tail;
rwlock.writeLock();
try
{
old_tail = tail;
if (seqno < head)
{
if (Trace.trace)
{
Trace.info("NakReceiverWindow.add()", "seqno " + seqno +
" is smaller than " + head + "); discarding message");
}
return;
}
// add at end (regular expected msg)
if (seqno == tail)
{
msgs.Add(new Entry(seqno, msg));
tail++;
}
// gap detected
// i. add placeholders, creating gaps
// ii. add real msg
// iii. tell retransmitter to retrieve missing msgs
else if (seqno > tail)
{
for (long i = tail; i < seqno; i++)
{
msgs.Add(new Entry(i, null));
tail++;
}
msgs.Add(new Entry(seqno, msg));
tail = seqno + 1;
if (retransmitter != null)
{
retransmitter.add(old_tail, seqno - 1);
}
// finally received missing message
}
else if (seqno < tail)
{
if (Trace.trace)
{
Trace.info("NakReceiverWindow.add()", "added missing msg " + msg.Source + "#" + seqno);
}
for (int i = 0; i < msgs.Count; i++)
{
current = (Entry)msgs[i];
// overwrite any previous message (e.g. added by down()) and
// remove seqno from retransmitter
if (seqno == current.seqno)
{
current.msg = msg;
if (retransmitter != null)
{
retransmitter.remove(seqno);
}
break;
}
}
}
_updateLowestSeen();
_updateHighestSeen();
}
finally
{
rwlock.writeUnlock();
}
}