private void WriteWorker(Stream stream, BlockingCollection <Block> toWrite, ColumnCodec[] activeColumns,
Schema sourceSchema, int rowsPerBlock, IChannelProvider cp, ExceptionMarshaller exMarshaller)
{
_host.AssertValue(exMarshaller);
try
{
_host.AssertValue(cp);
cp.AssertValue(stream);
cp.AssertValue(toWrite);
cp.AssertValue(activeColumns);
cp.AssertValue(sourceSchema);
cp.Assert(rowsPerBlock > 0);
using (IChannel ch = cp.Start("Write"))
{
var blockLookups = new List <BlockLookup> [activeColumns.Length];
for (int c = 0; c < blockLookups.Length; ++c)
{
blockLookups[c] = new List <BlockLookup>();
}
var deadLookups = new int[activeColumns.Length];
// Reserve space for the header at the start. This will be filled
// in with valid values once writing has completed.
ch.CheckIO(stream.Position == 0);
stream.Write(new byte[Header.HeaderSize], 0, Header.HeaderSize);
ch.CheckIO(stream.Position == Header.HeaderSize);
long expectedPosition = stream.Position;
BlockLookup deadLookup = new BlockLookup();
foreach (Block block in toWrite.GetConsumingEnumerable(exMarshaller.Token))
{
ch.CheckIO(stream.Position == expectedPosition);
MemoryStream compressed = block.BlockData;
ArraySegment <byte> buffer;
bool tmp = compressed.TryGetBuffer(out buffer);
ch.Assert(tmp);
stream.Write(buffer.Array, buffer.Offset, buffer.Count);
BlockLookup currLookup = new BlockLookup(expectedPosition, (int)compressed.Length, block.UncompressedLength);
expectedPosition += compressed.Length;
_memPool.Return(ref compressed);
ch.CheckIO(stream.Position == expectedPosition);
// Record the position. We have this "lookups" list per column. Yet, it may be that sometimes
// the writer receives things out of order.
// REVIEW: The format and the rest of the pipeline supposedly supports a long number
// of blocks, but the writing scheme does not yet support that.
int blockIndex = (int)block.BlockIndex;
var lookups = blockLookups[block.ColumnIndex];
if (lookups.Count == block.BlockIndex) // Received in order.
{
lookups.Add(currLookup);
}
else if (lookups.Count < block.BlockIndex) // Received a block a little bit early.
{
// Add a bunch of dead filler lookups, until these late blocks come in.
int deadToAdd = (int)block.BlockIndex - lookups.Count;
for (int i = 0; i < deadToAdd; ++i)
{
lookups.Add(deadLookup);
}
deadLookups[block.ColumnIndex] += deadToAdd;
ch.Assert(lookups.Count == block.BlockIndex);
lookups.Add(currLookup);
}
else // Received a block a little bit late.
{
// This should be a dead block unless the compressors are buggy and somehow
// yielding duplicate blocks or something.
ch.Assert(lookups[blockIndex].BlockOffset == 0);
deadLookups[block.ColumnIndex]--;
lookups[blockIndex] = currLookup;
}
}
// We have finished writing all blocks. We will now write the block lookup tables (so we can
// find the blocks), the slot names (for any columns that have them), the column table of
// contents (so we know how to decode the blocks, and where the lookups and names are),
// and the header (so we know dataview wide information and where to find the table of
// contents) in that order.
long[] lookupOffsets = new long[blockLookups.Length];
using (BinaryWriter writer = new BinaryWriter(stream, Encoding.UTF8, leaveOpen: true))
{
// Write the block lookup directories. These are referenced from the table of contents,
// so that someone knows where to look for some block data.
for (int c = 0; c < blockLookups.Length; ++c)
{
ch.Assert(deadLookups[c] == 0);
// The block lookup directories are written uncompressed and in fixed length
// to enable rapid seeking.
lookupOffsets[c] = stream.Position;
foreach (BlockLookup lookup in blockLookups[c])
{
// *** Lookup table entry format ***
// long: Offset to the start of a block
// int: Byte length of block as written
// int: Byte length of block when uncompressed
ch.Assert(lookup.BlockOffset > 0);
writer.Write(lookup.BlockOffset);
writer.Write(lookup.BlockLength);
writer.Write(lookup.DecompressedBlockLength);
}
ch.CheckIO(stream.Position == lookupOffsets[c] + (16 * blockLookups[c].Count),
"unexpected offsets after block lookup table write");
}
// Write the metadata for each column.
long[] metadataTocOffsets = new long[activeColumns.Length];
for (int c = 0; c < activeColumns.Length; ++c)
{
metadataTocOffsets[c] = WriteMetadata(writer, sourceSchema, activeColumns[c].SourceIndex, ch);
}
// Write the table of contents.
long tocOffset = stream.Position;
{
int c = 0;
expectedPosition = stream.Position;
foreach (var active in activeColumns)
{
// *** Column TOC entry format ***
// string: column name
// codec (as interpretable by CodecFactory.TryGetCodec): column block codec
// CompressionKind(byte): block compression strategy
// LEB128 int: Rows per block
// long: Offset to the start of the lookup table
// long: Offset to the start of the metadata TOC entries, or 0 if this has no metadata
string name = sourceSchema[active.SourceIndex].Name;
writer.Write(name);
int nameLen = Encoding.UTF8.GetByteCount(name);
expectedPosition += Utils.Leb128IntLength((uint)nameLen) + nameLen;
ch.CheckIO(stream.Position == expectedPosition, "unexpected offsets after table of contents name");
expectedPosition += _factory.WriteCodec(stream, active.Codec);
ch.CheckIO(stream.Position == expectedPosition, "unexpected offsets after table of contents type description");
writer.Write((byte)_compression);
expectedPosition++;
// REVIEW: Right now the number of rows per block is fixed, so we
// write the same value each time. In some future state, it may be that this
// is relaxed, with possibly some tradeoffs (for example, inability to randomly seek).
writer.WriteLeb128Int((ulong)rowsPerBlock);
expectedPosition += Utils.Leb128IntLength((uint)rowsPerBlock);
// Offset of the lookup table.
writer.Write(lookupOffsets[c]);
expectedPosition += sizeof(long);
// Offset of the metadata table of contents.
writer.Write(metadataTocOffsets[c]);
expectedPosition += sizeof(long);
ch.CheckIO(stream.Position == expectedPosition, "unexpected offsets after table of contents");
c++;
}
}
// Write the tail signature.
long tailOffset = stream.Position;
writer.Write(Header.TailSignatureValue);
// Now move back to the beginning of the stream, and write out the now completed header.
Header header = new Header()
{
Signature = Header.SignatureValue,
Version = Header.WriterVersion,
CompatibleVersion = Header.CanBeReadByVersion,
TableOfContentsOffset = tocOffset,
TailOffset = tailOffset,
RowCount = _rowCount,
ColumnCount = activeColumns.Length
};
byte[] headerBytes = new byte[Header.HeaderSize];
unsafe
{
Marshal.Copy(new IntPtr(&header), headerBytes, 0, Marshal.SizeOf(typeof(Header)));
}
writer.Seek(0, SeekOrigin.Begin);
writer.Write(headerBytes);
}
}
}
catch (Exception ex)
{
exMarshaller.Set("writing", ex);
}
}
