/// <summary>
/// insert this segment into cache, kick out other if needed
/// </summary>
/// <param name="seg"></param>
/// <precondition>seg is a new page brought in memory</precondition>
/// <postcondition>seg is insert into the cache, and the front of the LRU list, kick out one page if needed.</postcondition>
internal void _put_in_cache(Segment seg)
{
//if the cache is full, kick least recently used one out
if (m_cache.Count > m_cacheLimit)
{
//pick least recently used one
Segment victim = m_LRU.Prev;
Debug.Assert(victim != m_LRU);
if (victim.Dirty)
{
//write it out to the disk
byte[] content = victim.Serialize();
Debug.Assert(content.Length <= m_pageSize);
m_diskFile.SynWrite(content, 0, victim.SegmentID * m_pageSize, content.Length);
}
victim.BreakLinks();
bool t = m_cache.Delete(victim.SegmentID); //removed this one out of the cache
Debug.Assert(t);
}
if (m_cache.Insert(seg) == false)
{
throw new OOD.Exception.ProgramLogicError(
this,
"Trying to insert a existing key into CacheHashtable.");
}
seg.BuildLinks(m_LRU, m_LRU.Next); //move it the front of the LRU list
}
internal void _write_back(Segment seg)
{
//write it out to the disk
byte[] content = seg.Serialize();
//get its offset and length for the segment
uint offset = 0;
int length = -1;
if (m_segTree.GetAddr(seg.SegmentID, ref offset, ref length))
{
Debug.Assert(length != -1);
if (content.Length > length)
{
//original space is too small
//0. put original one fre
m_spaceTree.SetSegmentFree(offset, length);
//1. request a new segment with size = cotent.length + m_threshold;
if (m_spaceTree.RequireSegment(content.Length + m_threshold, ref offset) == false)
{
throw new OOD.Exception.ProgramLogicError(
this,
"Error happed while requesting free space.");
}
//3. update the new addressing in m_segTree.
if (m_segTree.UpdateAddr(seg.SegmentID, offset, content.Length + m_threshold) == false)
{
throw new OOD.Exception.ProgramLogicError(
this,
"Erro happened while updating addressing.");
}
}
else if (content.Length < length - m_threshold)
{
//original space is too big, shrink it to length + 256;
//1. update the addressing information in seqTree
// int newLength = content.Length + m_threshold;
// m_segTree.UpdateAddr(seg.SegmentID, offset, newLength);
//
// //2. insert the left empty space into the spaceTree
// uint leftOffset = (uint)(offset + newLength);
// newLength = length - newLength;
// m_spaceTree.SetSegmentFree(leftOffset, newLength);
}
}
else
{
Debug.Assert(length == -1);
//this is a new segment, it is never assigned adress before
//1. Request a free space
if (m_spaceTree.RequireSegment(content.Length + m_threshold, ref offset) == false)
{
throw new OOD.Exception.ProgramLogicError(
this,
"Request space failed.");
}
//2.put this into the m_segTree
if (m_segTree.InsertAddr(seg.SegmentID, offset, content.Length + m_threshold) == false)
{
throw new OOD.Exception.ProgramLogicError(
this,
"put segment addressing info failed in SegTree.");
}
}
m_diskFile.SynWrite(content, 0, offset, content.Length);
}
