// allocate a new node from free list or from pager
private BTreeNode GetNewNode(PageTypes nodeType)
{
// allocate
MemoryPage newPage = _freeList.AllocatePage();
if (newPage == null)
{
newPage = _pager.GetNewPage();
}
// initialize node
BTreeNode node = new BTreeNode(newPage, nodeType);
return(node);
}
static void TestFreeList()
{
string dbPath = "./testdbfile.minidb";
File.Delete(dbPath);
Pager pager = new Pager(dbPath, 4096, 100);
List <MemoryPage> pageList = new List <MemoryPage>();
pageList.Add(pager.GetNewPage()); // page #2
pageList.Add(pager.GetNewPage()); // page #3
pageList.Add(pager.GetNewPage()); // page #4
pageList.Add(pager.GetNewPage()); // page #5
FreeList freeList = new FreeList(pager);
// test initialization
MemoryPage newPage = null;
newPage = freeList.AllocatePage(); // freeList is now empty
Assert.Null(newPage);
// recycle pages
// MemoryPage tempPage = pager.ReadPage(3);
freeList.RecyclePage(pageList[2]); // freeList->4
freeList.RecyclePage(pageList[1]); // freeList->3->4
freeList.RecyclePage(pageList[3]); // freeList->5->3->4
// fetch page from free list
newPage = freeList.AllocatePage(); // freeList->3->4
Assert.Equal(5, newPage.PageNumber);
newPage = freeList.AllocatePage(); // freeList->4
Assert.Equal(3, newPage.PageNumber);
// recycle a page
freeList.RecyclePage(pageList[3]); // freeList->5->4
// fetch remaining pages
newPage = freeList.AllocatePage(); // freeList->4
Assert.Equal(5, newPage.PageNumber);
newPage = freeList.AllocatePage(); // freeList->null
Assert.Equal(4, newPage.PageNumber);
newPage = freeList.AllocatePage(); // freeList->null
Assert.Null(newPage);
pager.Close();
}