/// <summary>
/// Reads a list of items from persistent storage. The list is written as a chain of pages,
/// where the current page stores a pointer to the page storing the next range of items.
/// The items can be any "serializable" C# type.
/// </summary>
/// <param name="stream">data file to read from</param>
/// <param name="pageIdx">index of the page storing the head of the list</param>
/// <param name="list">list of items read</param>
/// <param name="pages">list of physical pages we read from</param>
public void ReadList(FileStreamWrapper stream, int pageIdx, out List <T> list, out List <int> pages)
{
// read pages one by one
while (ListHdr.EOLPageIndex != pageIdx)
{
// read the page data
StoragePage page = new StoragePage();
int readPage = page.ReadPageData(stream, pageIdx);
if (readPage != pageIdx)
{
throw new InvalidListException();
}
// read the header
ListHdr header = (ListHdr)page.ReadRecord(ListHdr.HeaderRecordIdx);
if (null == header)
{
throw new InvalidListException();
}
// process the page
this.ReadCurrentPage(page, header.PageEntriesCount);
// update the page index
this.pageList.Add(pageIdx);
pageIdx = header.NextPageIndex;
}
// set the output variables
list = this.itemList;
pages = this.pageList;
}
private void CreateNewPage(int count, StoragePageManager freeSpaceMgr)
{
// create a new header object
ListHdr header = new ListHdr()
{
NextPageIndex = ListHdr.EOLPageIndex,
TotalEntriesCount = count,
PageEntriesCount = 0,
PageWriteIndex = freeSpaceMgr.GetFreePage()
};
this.pageHeaderList.Push(header);
// create the page - and write a placeholder record for the header
StoragePage page = new StoragePage();
page.AddRecord(header);
this.pageList.Push(page);
}
private int WriteTopPage(FileStreamWrapper stream, int lastPageAddress)
{
// update the header
ListHdr header = this.pageHeaderList.Pop();
header.NextPageIndex = lastPageAddress;
// update the page
StoragePage page = this.pageList.Pop();
page.WriteRecord(ListHdr.HeaderRecordIdx, header);
// get the page to write to
int pageIdx = header.PageWriteIndex;
// write the page
pageIdx = page.WritePageData(stream, pageIdx);
this.pageIdxList.Insert(0, pageIdx);
return(pageIdx);
}
