C++ SerializeOutput::position方法代码示例

void Table::serializeTo(SerializeOutput &serialOutput) {
    // The table is serialized as:
    // [(int) total size]
    // [(int) header size] [num columns] [column types] [column names]
    // [(int) num tuples] [tuple data]

    /* NOTE:
       VoltDBEngine uses a binary template to create tables of single integers.
       It's called m_templateSingleLongTable and if you are seeing a serialization
       bug in tables of single integers, make sure that's correct.
    */

    // a placeholder for the total table size
    std::size_t pos = serialOutput.position();
    serialOutput.writeInt(-1);

    serializeColumnHeaderTo(serialOutput);

    // active tuple counts
    serialOutput.writeInt(static_cast<int32_t>(m_tupleCount));
    int64_t written_count = 0;
    TableIterator titer = iterator();
    TableTuple tuple(m_schema);
    while (titer.next(tuple)) {
        tuple.serializeTo(serialOutput);
        ++written_count;
    }
    assert(written_count == m_tupleCount);

    // length prefix is non-inclusive
    int32_t sz = static_cast<int32_t>(serialOutput.position() - pos - sizeof(int32_t));
    assert(sz > 0);
    serialOutput.writeIntAt(pos, sz);
}

void Table::serializeColumnHeaderTo(SerializeOutput &serialOutput) {
    /* NOTE:
       VoltDBEngine uses a binary template to create tables of single integers.
       It's called m_templateSingleLongTable and if you are seeing a serialization
       bug in tables of single integers, make sure that's correct.
    */

    // skip header position
    std::size_t start;

    // use a cache
    if (m_columnHeaderData) {
        assert(m_columnHeaderSize != -1);
        serialOutput.writeBytes(m_columnHeaderData, m_columnHeaderSize);
        return;
    }
    assert(m_columnHeaderSize == -1);

    start = serialOutput.position();

    // skip header position
    serialOutput.writeInt(-1);

    //status code
    serialOutput.writeByte(-128);

    // column counts as a short
    serialOutput.writeShort(static_cast<int16_t>(m_columnCount));

    // write an array of column types as bytes
    for (int i = 0; i < m_columnCount; ++i) {
        ValueType type = m_schema->columnType(i);
        serialOutput.writeByte(static_cast<int8_t>(type));
    }

    // write the array of column names as voltdb strings
    // NOTE: strings are ASCII only in metadata (UTF-8 in table storage)
    for (int i = 0; i < m_columnCount; ++i) {
        // column name: write (offset, length) for column definition, and string to string table
        const string& name = columnName(i);
        // column names can't be null, so length must be >= 0
        int32_t length = static_cast<int32_t>(name.size());
        assert(length >= 0);

        // this is standard string serialization for voltdb
        serialOutput.writeInt(length);
        serialOutput.writeBytes(name.data(), length);
    }


    // write the header size which is a non-inclusive int
    size_t position = serialOutput.position();
    m_columnHeaderSize = static_cast<int32_t>(position - start);
    int32_t nonInclusiveHeaderSize = static_cast<int32_t>(m_columnHeaderSize - sizeof(int32_t));
    serialOutput.writeIntAt(start, nonInclusiveHeaderSize);

    // cache the results
    m_columnHeaderData = new char[m_columnHeaderSize];
    memcpy(m_columnHeaderData, static_cast<const char*>(serialOutput.data()) + start, m_columnHeaderSize);
}

bool Table::serializeTo(int32_t offset, int32_t limit, SerializeOutput &serialize_io) {
    // The table is serialized as:
    // [(int) total size]
    // [(int) header size] [num columns] [column types] [column names]
    // [(int) num tuples] [tuple data]

    /* NOTE:
       VoltDBEngine uses a binary template to create tables of single integers.
       It's called m_templateSingleLongTable and if you are seeing a serialization
       bug in tables of single integers, make sure that's correct.
    */

    // a placeholder for the total table size
    std::size_t pos = serialize_io.position();
    serialize_io.writeInt(-1);

    if (!serializeColumnHeaderTo(serialize_io))
        return false;

    // active tuple counts
    uint32_t output_size = m_tupleCount;
    if (limit != -1 || offset != -1) {
        if (offset == -1) {
            output_size = (limit < m_tupleCount ? limit : m_tupleCount);
        } else if (offset > m_tupleCount) {
            output_size = 0;
        } else {
            output_size = m_tupleCount - offset;
            if (limit != -1 && limit < output_size) output_size = limit;
        }
    }
    serialize_io.writeInt(static_cast<int32_t>(output_size));
//     fprintf(stderr, "SERIALIZE(output=%d, offset=%d, limit=%d, total=%d)\n", output_size, offset, limit, m_tupleCount);
    
    int64_t written_count = 0;
    int64_t read_count = 0;
    TableIterator titer(this);
    TableTuple tuple(m_schema);
    while (titer.next(tuple)) {
        if (offset == -1 || read_count >= offset) {
            tuple.serializeTo(serialize_io);
            if (limit != -1 && ++written_count == limit) break;
        }
        read_count++;
    }
    // assert(written_count == m_tupleCount);

    // length prefix is non-inclusive
    int32_t sz = static_cast<int32_t>(serialize_io.position() - pos - sizeof(int32_t));
    assert(sz > 0);
    serialize_io.writeIntAt(pos, sz);

    return true;
}

/**
 * Serialized the table, but only includes the tuples specified (columns data and all).
 * Used by the exception stuff Ariel put in.
 */
void Table::serializeTupleTo(SerializeOutput &serialOutput, voltdb::TableTuple *tuples, int numTuples) {
    //assert(m_schema->equals(tuples[0].getSchema()));

    std::size_t pos = serialOutput.position();
    serialOutput.writeInt(-1);

    assert(!tuples[0].isNullTuple());

    serializeColumnHeaderTo(serialOutput);

    serialOutput.writeInt(static_cast<int32_t>(numTuples));
    for (int ii = 0; ii < numTuples; ii++) {
        tuples[ii].serializeTo(serialOutput);
    }

    serialOutput.writeIntAt(pos, static_cast<int32_t>(serialOutput.position() - pos - sizeof(int32_t)));
}