private ReadResult Read()
{
if (_loadMore)
{
if (_remaining != 0)
{
var take = (int)Math.Min(_remaining, _pageSize);
DebugLog($"Loading {take} bytes from offet {_offset}...");
var accessor = _file.CreateViewAccessor(_offset, take, MemoryMappedFileAccess.Read);
var next = new MappedPage(accessor, _offset, take);
Debug.Assert(next.RunningIndex == _offset);
_remaining -= take;
_offset += take;
if (_first == null)
{
_first = _last = next;
}
else
{
_last.Next = next;
_last = next;
}
DebugLog($"Loaded page {next}");
}
_loadMore = false;
}
if (_first == null)
{
Debug.Assert(_remaining == 0, "unexpected EOF");
DebugLog($"Read has encountered EOF");
return(new ReadResult(default, false, true));
private static long CountAvailable(MappedPage page)
{
long total = 0;
while (page != null)
{
total += page.Capacity - page.Consumed;
page = page.Next;
}
return(total);
}
/// <summary>
/// Releases all resources associated with the object
/// </summary>
public void Dispose()
{
var page = _first;
while (page != null)
{
try { page.Dispose(); } catch { }
page = page.Next;
}
_first = _last = null;
try { _file?.Dispose(); } catch { }
_file = null;
}
/// <summary>
/// Indicates how much data was consumed, and how much examined, from a read operation
/// </summary>
public override void AdvanceTo(SequencePosition consumed, SequencePosition examined)
{
var cPage = (MappedPage)consumed.GetObject();
var ePage = (MappedPage)examined.GetObject();
if (cPage == null || ePage == null)
{
if (_first == null)
{
return; // that's fine - means they called Advance on an empty EOF
}
Throw.Argument("Invalid position; consumed/examined must remain inside the buffer");
}
Debug.Assert(ePage != null, "No examined page");
Debug.Assert(cPage != null, "No consumed page");
MappedPage newKeep;
var cOffset = consumed.GetInteger();
if (cOffset == cPage.Capacity)
{
newKeep = cPage.Next;
}
else
{
newKeep = cPage;
newKeep.Consumed = cOffset;
}
if (newKeep == null)
{
DebugLog($"Retaining nothing");
_last = null;
}
else
{
DebugLog($"Retaining page {newKeep}");
}
// now drop any pages we don't need
if (newKeep != _first)
{
var page = _first;
while (page != null && page != newKeep)
{
DebugLog($"Dropping page {page}");
page.Dispose();
page = page.Next;
}
_first = newKeep;
}
// check whether they looked at everything
if (_last == null)
{
_loadMore = true; // definitely
}
else
{
var eOffset = examined.GetInteger();
_loadMore = ePage == _last && eOffset == ePage.Capacity;
}
DebugLog($"After AdvanceTo, {CountAvailable(_first)} available bytes, {_remaining} remaining unloaded bytes, load more: {_loadMore}");
}
