ClickHouse/src/IO/WriteBufferFromVector.h

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#pragma once
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#include <vector>
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#include <IO/WriteBuffer.h>
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namespace DB
{
namespace ErrorCodes
{
extern const int CANNOT_WRITE_AFTER_END_OF_BUFFER;
}
struct AppendModeTag {};
/** Writes data to existing std::vector or similar type. When not enough space, it doubles vector size.
*
* In destructor, vector is cut to the size of written data.
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* You can call 'finalize' to resize earlier.
*
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* The vector should live until this object is destroyed or until the 'finalizeImpl()' method is called.
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*/
template <typename VectorType>
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class WriteBufferFromVector : public WriteBuffer
{
public:
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explicit WriteBufferFromVector(VectorType & vector_)
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: WriteBuffer(reinterpret_cast<Position>(vector_.data()), vector_.size()), vector(vector_)
{
if (vector.empty())
{
vector.resize(initial_size);
set(reinterpret_cast<Position>(vector.data()), vector.size());
}
}
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/// Append to vector instead of rewrite.
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WriteBufferFromVector(VectorType & vector_, AppendModeTag)
: WriteBuffer(nullptr, 0), vector(vector_)
{
size_t old_size = vector.size();
size_t size = (old_size < initial_size) ? initial_size
: ((old_size < vector.capacity()) ? vector.capacity()
: vector.capacity() * size_multiplier);
vector.resize(size);
set(reinterpret_cast<Position>(vector.data() + old_size), (size - old_size) * sizeof(typename VectorType::value_type));
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}
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bool isFinished() const { return finalized; }
void restart()
{
if (vector.empty())
vector.resize(initial_size);
set(reinterpret_cast<Position>(vector.data()), vector.size());
finalized = false;
}
~WriteBufferFromVector() override
{
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finalize();
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}
private:
void finalizeImpl() override final
{
vector.resize(
((position() - reinterpret_cast<Position>(vector.data())) /// NOLINT
+ sizeof(typename VectorType::value_type) - 1) /// Align up.
/ sizeof(typename VectorType::value_type));
/// Prevent further writes.
set(nullptr, 0);
}
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void nextImpl() override
{
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if (finalized)
throw Exception("WriteBufferFromVector is finalized", ErrorCodes::CANNOT_WRITE_AFTER_END_OF_BUFFER);
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size_t old_size = vector.size();
/// pos may not be equal to vector.data() + old_size, because WriteBuffer::next() can be used to flush data
size_t pos_offset = pos - reinterpret_cast<Position>(vector.data());
vector.resize(old_size * size_multiplier);
internal_buffer = Buffer(reinterpret_cast<Position>(vector.data() + pos_offset), reinterpret_cast<Position>(vector.data() + vector.size()));
working_buffer = internal_buffer;
}
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VectorType & vector;
static constexpr size_t initial_size = 32;
static constexpr size_t size_multiplier = 2;
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};
}