private void AllocateNextSegment(int required, bool allowGrowth)
{
//TODO: protect from documents larger than 1GB
// grow by doubling segment size until we get to 1 MB, then just use 1 MB segments
// otherwise a document with 17 MB will waste 15 MB and require very big allocations
var nextSegmentSize = Math.Max(Bits.NextPowerOf2(required), _current.Allocation.SizeInBytes * 2);
const int oneMb = 1024 * 1024;
if (nextSegmentSize > oneMb && required <= oneMb)
{
nextSegmentSize = oneMb;
}
if (allowGrowth &&
// we successfully grew the allocation, nothing to do
_context.GrowAllocation(_current.Allocation, nextSegmentSize))
{
return;
}
var allocatedMemoryData = _context.GetMemory(nextSegmentSize);
_current = new Segment
{
Address = (byte *)allocatedMemoryData.Address,
Allocation = allocatedMemoryData,
Used = 0,
Previous = _current,
PreviousAllocated = _current
};
}
private void AllocateNextSegment(int required, bool allowGrowth)
{
Debug.Assert(required > 0);
if (required > ArenaMemoryAllocator.MaxArenaSize)
{
ThrowOnAllocationSizeExceeded(required, ArenaMemoryAllocator.MaxArenaSize);
}
// Grow by doubling segment size until we get to 1 MB, then just use 1 MB segments
// otherwise a document with 17 MB will waste 15 MB and require very big allocations
var requiredPowerOfTwo = Bits.PowerOf2(required);
var segmentSize = Math.Max(requiredPowerOfTwo, _head.Allocation.SizeInBytes * 2);
const int oneMb = 1024 * 1024;
if (segmentSize > oneMb && required <= oneMb)
{
segmentSize = oneMb;
}
// We can sometimes ask the context to grow the allocation size;
// it may do so at its own discretion; if this happens, then we
// are good to go.
if (allowGrowth && _context.GrowAllocation(_head.Allocation, segmentSize))
{
return;
}
// Can't change _head because there may be copies of the current
// instance of UnmanagedWriteBuffer going around. Thus, we simply
// mutate it to ensure all copies have the same allocations.
var allocation = _context.GetMemory(segmentSize);
if (allocation.SizeInBytes < required)
{
ThrowOnAllocationSizeMismatch(allocation.SizeInBytes, required);
}
// Copy the head
Segment previousHead = _head.ShallowCopy();
// Reset the head (this change happens in all instances at the
// same time, albeit not atomically).
_head.Previous = previousHead;
_head.DeallocationPendingPrevious = previousHead;
_head.Allocation = allocation;
_head.Address = allocation.Address;
_head.Used = 0;
_head.AccumulatedSizeInBytes = previousHead.AccumulatedSizeInBytes;
}