void MapContent()
{
if (_accessor != null) return;
_memoryMappedFile = MemoryMappedFile.CreateFromFile(_stream, null, 0, MemoryMappedFileAccess.ReadWrite, null, HandleInheritability.None, true);
_accessor = _memoryMappedFile.CreateViewAccessor();
_accessor.SafeMemoryMappedViewHandle.AcquirePointer(ref _pointer);
}