private LoadedPage MapPages(TransactionState state, long startPage, long size)
{
var offset = new Win32MemoryMapPager.SplitValue {
Value = (ulong)startPage * (ulong)PageSize
};
if ((long)offset.Value + size > _fileStreamLength)
{
size = _fileStreamLength - (long)offset.Value;
}
var result = MapViewOfFileEx(_hFileMappingObject, _mmFileAccessType, offset.High,
offset.Low,
(UIntPtr)size, null);
if (result == null)
{
throw new Win32Exception();
}
state.AddressesToUnload.Add(new IntPtr(result));
var loadedPage = new LoadedPage
{
Pointer = result,
NumberOfPages = (int)(size / PageSize),
StartPage = startPage
};
state.LoadedPages[startPage] = loadedPage;
return(loadedPage);
}
public override int CopyPage(IPagerBatchWrites destPagerBatchWrites, long pageNumber, PagerState pagerState)
{
var distanceFromStart = (pageNumber % 16);
var allocationStartPosition = pageNumber - distanceFromStart;
var offset = new Win32MemoryMapPager.SplitValue {
Value = (ulong)allocationStartPosition * (ulong)PageSize
};
var result = MapViewOfFileEx(_hFileMappingObject, _mmFileAccessType, offset.High,
offset.Low,
(UIntPtr)(16 * PageSize), null);
if (result == null)
{
throw new Win32Exception();
}
var pageHeader = (PageHeader *)(result + distanceFromStart * PageSize);
int numberOfPages = 1;
if ((pageHeader->Flags & PageFlags.Overflow) == PageFlags.Overflow)
{
numberOfPages = this.GetNumberOfOverflowPages(pageHeader->OverflowSize);
}
if (numberOfPages + distanceFromStart > 16)
{
UnmapViewOfFile(result);
result = MapViewOfFileEx(_hFileMappingObject, _mmFileAccessType, offset.High,
offset.Low,
(UIntPtr)(NearestSizeToAllocationGranularity((numberOfPages + distanceFromStart) * PageSize)), null);
if (result == null)
{
throw new Win32Exception();
}
pageHeader = (PageHeader *)(result + (distanceFromStart * PageSize));
}
destPagerBatchWrites.Write(pageHeader->PageNumber, numberOfPages, (byte *)pageHeader);
UnmapViewOfFile(result);
return(numberOfPages);
}