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);
}
private byte *ReturnPagePointerOrGrowAllocation(LoadedPage page, long distanceFromStart, TransactionState state, bool canUnmap)
{
var pageHeader = (PageHeader *)(page.Pointer + (distanceFromStart * PageSize));
if ((pageHeader->Flags & PageFlags.Overflow) != PageFlags.Overflow)
{
// single page, already loaded, can return immediately.
return((byte *)pageHeader);
}
// overflow, so need to make sure it is in the range we mapped.
var numberOfOverflowPages = this.GetNumberOfOverflowPages(pageHeader->OverflowSize);
if (numberOfOverflowPages + distanceFromStart < page.NumberOfPages)
{
// the entire range is already mapped, can return immediately
return((byte *)pageHeader);
}
if (canUnmap)
{
Debug.Assert(state.AddressesToUnload[state.AddressesToUnload.Count - 1] == new IntPtr(page.Pointer));
state.AddressesToUnload.RemoveAt(state.AddressesToUnload.Count - 1);
UnmapViewOfFile(page.Pointer);
}
var ammountToMapInBytes = NearestSizeToAllocationGranularity((distanceFromStart + numberOfOverflowPages) * PageSize);
page = MapPages(state, page.StartPage, ammountToMapInBytes);
return(page.Pointer + distanceFromStart * PageSize);
}
private LoadedPage AddMappingToTransaction(TransactionState state, long startPage, long size, MappedAddresses mappedAddresses)
{
state.TotalLoadedSize += size;
state.AddressesToUnload.Add(mappedAddresses);
var loadedPage = new LoadedPage
{
Pointer = (byte *)mappedAddresses.Address,
NumberOfPages = (int)(size / Constants.Storage.PageSize),
StartPage = startPage
};
state.LoadedPages[startPage] = loadedPage;
return(loadedPage);
}
