public Stream Dequeue()
{
lock (_lockObject)
{
if (_metaData.HeadIndex == _metaData.TailIndex) // Head cought up with tail. Queue is empty.
{
return(null); // return null or Stream.Null?
}
// Delete previous index page if we are moving along to the next
if (GetIndexPageIndex(_metaData.HeadIndex) != _headIndexPageIndex)
{
_indexPageFactory.DeletePage(_headIndexPageIndex);
_headIndexPageIndex = GetIndexPageIndex(_metaData.HeadIndex);
}
// Get index item for head index
var indexItem = GetIndexItem(_metaData.HeadIndex);
// Delete previous data page if we are moving along to the next
if (indexItem.DataPageIndex != _headDataPageIndex)
{
_dataPageFactory.DeletePage(_headDataPageIndex);
_headDataPageIndex = indexItem.DataPageIndex;
}
// Get data page
var dataPage = _dataPageFactory.GetPage(indexItem.DataPageIndex);
// Get read stream
MemoryStream memoryStream = new MemoryStream();
using (var readStream = dataPage.GetReadStream(indexItem.ItemOffset, indexItem.ItemLength))
{
readStream.CopyTo(memoryStream, 4 * 1024);
memoryStream.Position = 0;
}
_dataPageFactory.ReleasePage(dataPage.Index);
// Update meta data
if (_metaData.HeadIndex == long.MaxValue)
{
_metaData.HeadIndex = 0;
}
else
{
_metaData.HeadIndex++;
}
PersistMetaData();
return(memoryStream);
}
}
private void CommitBatch(ItemRange range)
{
var newHeadIndex = range.HeadIndex + range.ItemCount;
long oldHeadIndex;
lock (_lockObject)
{
// Update meta data
oldHeadIndex = _metaData.HeadIndex;
if (newHeadIndex > oldHeadIndex)
{
_metaData.HeadIndex = newHeadIndex;
}
PersistMetaData();
}
if (newHeadIndex > oldHeadIndex)
{
var lastHeadIndex = GetPreviousIndex(oldHeadIndex);
var lastWrittenIndex = GetPreviousIndex(newHeadIndex);
var oldHeadIndexItem = GetIndexItem(lastHeadIndex);
var lastWrittenIndexItem = GetIndexItem(lastWrittenIndex);
for (var dataPageIndex = oldHeadIndexItem.DataPageIndex;
dataPageIndex < lastWrittenIndexItem.DataPageIndex;
dataPageIndex++)
{
_dataPageFactory.DeletePage(dataPageIndex);
}
for (var indexPageIndex = GetIndexPageIndex(lastHeadIndex);
indexPageIndex < GetIndexPageIndex(lastWrittenIndex);
indexPageIndex++)
{
_indexPageFactory.DeletePage(indexPageIndex);
}
}
}