public void CheckForAllocateComplete(ref long address)
{
if (address >= 0)
{
throw new Exception("Address already allocated!");
}
PageOffset p = default(PageOffset);
p.Page = (int)((-address) >> LogPageSizeBits);
p.Offset = (int)((-address) & PageSizeMask);
//Check write cache
int pageIndex = p.Page % BufferSize;
if (TailPageIndex == pageIndex)
{
address = -address;
return;
}
//Check if we can move the head offset
long currentTailAddress = GetTailAddress();
PageAlignedShiftHeadAddress(currentTailAddress);
//Check if I can allocate pageIndex at all
if ((PageStatusIndicator[pageIndex].PageFlushCloseStatus.PageFlushStatus != FlushStatus.Flushed) ||
(PageStatusIndicator[pageIndex].PageFlushCloseStatus.PageCloseStatus != CloseStatus.Closed) ||
(values[pageIndex] == null))
{
return;
}
//correct values and set write cache
address = -address;
if (p.Offset == 0)
{
TailPageIndex = pageIndex;
}
return;
}
public long Allocate(int numSlots = 1)
{
PageOffset localTailPageOffset = default(PageOffset);
// Determine insertion index.
// ReSharper disable once CSharpWarnings::CS0420
#pragma warning disable 420
localTailPageOffset.PageAndOffset = Interlocked.Add(ref TailPageOffset.PageAndOffset, numSlots);
#pragma warning restore 420
int page = localTailPageOffset.Page;
int offset = localTailPageOffset.Offset - numSlots;
#region HANDLE PAGE OVERFLOW
/* To prove correctness of the following modifications
* done to TailPageOffset and the allocation itself,
* we should use the fact that only one thread will have any
* of the following cases since it is a counter and we spin-wait
* until the tail is folded onto next page accordingly.
*/
if (localTailPageOffset.Offset >= PageSize)
{
if (offset >= PageSize)
{
//The tail offset value was more than page size before atomic add
//We consider that a failed attempt and retry again
var spin = new SpinWait();
do
{
//Just to give some more time to the thread
// that is handling this overflow
while (TailPageOffset.Offset >= PageSize)
{
spin.SpinOnce();
}
// ReSharper disable once CSharpWarnings::CS0420
#pragma warning disable 420
localTailPageOffset.PageAndOffset = Interlocked.Add(ref TailPageOffset.PageAndOffset, numSlots);
#pragma warning restore 420
page = localTailPageOffset.Page;
offset = localTailPageOffset.Offset - numSlots;
} while (offset >= PageSize);
}
if (localTailPageOffset.Offset == PageSize)
{
//Folding over at page boundary
localTailPageOffset.Page++;
localTailPageOffset.Offset = 0;
TailPageOffset = localTailPageOffset;
}
else if (localTailPageOffset.Offset >= PageSize)
{
//Overflows not allowed. We allot same space in next page.
localTailPageOffset.Page++;
localTailPageOffset.Offset = numSlots;
TailPageOffset = localTailPageOffset;
page = localTailPageOffset.Page;
offset = 0;
}
}
#endregion
long address = (((long)page) << LogPageSizeBits) | ((long)offset);
// Check if TailPageIndex is appropriate and allocated!
int pageIndex = page % BufferSize;
if (TailPageIndex == pageIndex)
{
return(address);
}
//Invert the address if either the previous page is not flushed or if it is null
if ((PageStatusIndicator[pageIndex].PageFlushCloseStatus.PageFlushStatus != FlushStatus.Flushed) ||
(PageStatusIndicator[pageIndex].PageFlushCloseStatus.PageCloseStatus != CloseStatus.Closed) ||
(values[pageIndex] == null))
{
address = -address;
}
// Update the read-only so that we can get more space for the tail
if (offset == 0)
{
if (address >= 0)
{
TailPageIndex = pageIndex;
Interlocked.MemoryBarrier();
}
long newPage = page + 1;
int newPageIndex = (int)((page + 1) % BufferSize);
long tailAddress = (address < 0 ? -address : address);
PageAlignedShiftReadOnlyAddress(tailAddress);
PageAlignedShiftHeadAddress(tailAddress);
if (values[newPageIndex] == null)
{
AllocatePage(newPageIndex);
}
}
return(address);
}