EventStore.Core.Index.PTable.PTable C# (CSharp) Method

        private PTable(string filename,
                       Guid id,
                       int initialReaders = ESConsts.PTableInitialReaderCount,
                       int maxReaders = ESConsts.PTableMaxReaderCount,
                       int depth = 16)
        {
            Ensure.NotNullOrEmpty(filename, "filename");
            Ensure.NotEmptyGuid(id, "id");
            Ensure.Positive(maxReaders, "maxReaders");
            Ensure.Nonnegative(depth, "depth");

            if (!File.Exists(filename))
                throw new CorruptIndexException(new PTableNotFoundException(filename));

            _id = id;
            _filename = filename;

            Log.Trace("Loading and Verification of PTable '{0}' started...", Path.GetFileName(Filename));
            var sw = Stopwatch.StartNew();
            _size = new FileInfo(_filename).Length;

            File.SetAttributes(_filename, FileAttributes.ReadOnly | FileAttributes.NotContentIndexed);

            _workItems = new ObjectPool<WorkItem>(string.Format("PTable {0} work items", _id),
                                                  initialReaders,
                                                  maxReaders,
                                                  () => new WorkItem(filename, DefaultBufferSize),
                                                  workItem => workItem.Dispose(),
                                                  pool => OnAllWorkItemsDisposed());

            var readerWorkItem = GetWorkItem();
            try
            {
                readerWorkItem.Stream.Seek(0, SeekOrigin.Begin);
                var header = PTableHeader.FromStream(readerWorkItem.Stream);
                if ((header.Version != PTableVersions.Index32Bit) &&
                    (header.Version != PTableVersions.Index64Bit))
                    throw new CorruptIndexException(new WrongFileVersionException(_filename, header.Version, Version));
                _version = header.Version;

                if (_version == PTableVersions.Index32Bit)
                {
                    _indexEntrySize = IndexEntry32Size;
                    _indexKeySize = IndexKey32Size;
                }
                if (_version == PTableVersions.Index64Bit)
                {
                    _indexEntrySize = IndexEntry64Size;
                    _indexKeySize = IndexKey64Size;
                }
                _count = ((_size - PTableHeader.Size - MD5Size) / _indexEntrySize);

                if (Count == 0)
                {
                    _minEntry = new IndexEntryKey(ulong.MaxValue, int.MaxValue);
                    _maxEntry = new IndexEntryKey(ulong.MinValue, int.MinValue);
                }
                else
                {
                    var minEntry = ReadEntry(_indexEntrySize, Count - 1, readerWorkItem, _version);
                    _minEntry = new IndexEntryKey(minEntry.Stream, minEntry.Version);
                    var maxEntry = ReadEntry(_indexEntrySize, 0, readerWorkItem, _version);
                    _maxEntry = new IndexEntryKey(maxEntry.Stream, maxEntry.Version);
                }
            }
            catch (Exception)
            {
                Dispose();
                throw;
            }
            finally
            {
                ReturnWorkItem(readerWorkItem);
            }
            int calcdepth = 0;
            try
            {
                calcdepth = GetDepth(_size, depth);
                _midpoints = CacheMidpointsAndVerifyHash(calcdepth);
            }
            catch (PossibleToHandleOutOfMemoryException)
            {
                Log.Error("Unable to create midpoints for PTable '{0}' ({1} entries, depth {2} requested). "
                          + "Performance hit will occur. OOM Exception.", Path.GetFileName(Filename), Count, depth);
            }
            Log.Trace("Loading PTable (Version: {0}) '{1}' ({2} entries, cache depth {3}) done in {4}.",
                      _version, Path.GetFileName(Filename), Count, calcdepth, sw.Elapsed);
        }