ClickHouse/dbms/include/DB/IO/BufferWithOwnMemory.h

#pragma once

#include <boost/noncopyable.hpp>

#include <DB/Common/ProfileEvents.h>
#include <DB/Common/Allocator.h>

#include <DB/Common/Exception.h>
#include <DB/Core/Defines.h>


namespace ProfileEvents
{
	extern const Event IOBufferAllocs;
	extern const Event IOBufferAllocBytes;
}


namespace DB
{


/** Replacement for std::vector<char> to use in buffers.
  * Differs in that is doesn't do unneeded memset. (And also tries to do as little as possible.)
  * Also allows to allocate aligned piece of memory (to use with O_DIRECT, for example).
  */
struct Memory : boost::noncopyable, Allocator<false>
{
	size_t m_capacity = 0;
	size_t m_size = 0;
	char * m_data = nullptr;
	size_t alignment = 0;

    Memory() {}

	/// If alignment != 0, then allocate memory aligned to specified value.
	Memory(size_t size_, size_t alignment_ = 0) : m_capacity(size_), m_size(m_capacity), alignment(alignment_)
	{
		alloc();
	}

	~Memory()
	{
		dealloc();
	}

	Memory(Memory && rhs)
	{
		*this = std::move(rhs);
	}

	Memory & operator=(Memory && rhs)
	{
		std::swap(m_capacity, rhs.m_capacity);
		std::swap(m_size, rhs.m_size);
		std::swap(m_data, rhs.m_data);
		std::swap(alignment, rhs.alignment);

		return *this;
	}

	size_t size() const { return m_size; }
	const char & operator[](size_t i) const { return m_data[i]; }
	char & operator[](size_t i) { return m_data[i]; }
	const char * data() const { return m_data; }
	char * data() { return m_data; }

	void resize(size_t new_size)
	{
		if (0 == m_capacity)
		{
			m_size = m_capacity = new_size;
			alloc();
		}
		else if (new_size < m_capacity)
		{
			m_size = new_size;
			return;
		}
		else
		{
			new_size = align(new_size, alignment);
			m_data = static_cast<char *>(Allocator::realloc(m_data, m_capacity, new_size, alignment));
			m_capacity = new_size;
			m_size = m_capacity;
		}
	}

	static size_t align(const size_t value, const size_t alignment)
	{
		if (!alignment)
			return value;

		return (value + alignment - 1) / alignment * alignment;
	}

private:
	void alloc()
	{
		if (!m_capacity)
		{
			m_data = nullptr;
			return;
		}

		ProfileEvents::increment(ProfileEvents::IOBufferAllocs);
		ProfileEvents::increment(ProfileEvents::IOBufferAllocBytes, m_capacity);

		size_t new_capacity = align(m_capacity, alignment);
		m_data = static_cast<char *>(Allocator::alloc(new_capacity, alignment));
		m_capacity = new_capacity;
		m_size = m_capacity;
	}

	void dealloc()
	{
		if (!m_data)
			return;

		Allocator::free(m_data, m_capacity);
		m_data = nullptr;	/// To avoid double free if next alloc will throw an exception.
	}
};


/** Buffer that could own its working memory.
  * Template parameter: ReadBuffer or WriteBuffer
  */
template <typename Base>
class BufferWithOwnMemory : public Base
{
protected:
	Memory memory;
public:
	/// If non-nullptr 'existing_memory' is passed, then buffer will not create its own memory and will use existing_memory without ownership.
	BufferWithOwnMemory(size_t size = DBMS_DEFAULT_BUFFER_SIZE, char * existing_memory = nullptr, size_t alignment = 0)
		: Base(nullptr, 0), memory(existing_memory ? 0 : size, alignment)
	{
		Base::set(existing_memory ? existing_memory : memory.data(), size);
	}
};


}