mariadb/storage/innobase/include/dyn0buf.h

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/**************************************************//**
@file include/dyn0buf.h
The dynamically allocated buffer implementation

Created 2013-03-16 Sunny Bains
*******************************************************/

#ifndef dyn0buf_h
#define dyn0buf_h

#include "mem0mem.h"
#include "dyn0types.h"
#include "ilist.h"


/** Class that manages dynamic buffers. It uses a UT_LIST of
mtr_buf_t::block_t instances. We don't use STL containers in
order to avoid the overhead of heap calls. Using a custom memory
allocator doesn't solve the problem either because we have to get
the memory from somewhere. We can't use the block_t::m_data as the
backend for the custom allocator because we would like the data in
the blocks to be contiguous. */
class mtr_buf_t {
public:
	/** SIZE - sizeof(m_node) + sizeof(m_used) */
	enum { MAX_DATA_SIZE = DYN_ARRAY_DATA_SIZE
	       - sizeof(ilist_node<>) + sizeof(uint32_t) };

	class block_t : public ilist_node<> {
	public:

		block_t()
		{
			compile_time_assert(MAX_DATA_SIZE <= (2 << 15));
			init();
		}

		/**
		Gets the number of used bytes in a block.
		@return	number of bytes used */
		uint32_t used() const { return m_used; }

		/**
		Gets pointer to the start of data.
		@return	pointer to data */
		byte* start()
			MY_ATTRIBUTE((warn_unused_result))
		{
			return(m_data);
		}

		/**
		@return start of data - non const version */
		byte* begin()
			MY_ATTRIBUTE((warn_unused_result))
		{
			return(m_data);
		}

		/**
		@return end of used data - non const version */
		byte* end()
			MY_ATTRIBUTE((warn_unused_result))
		{
			return(begin() + m_used);
		}

		/**
		@return start of data - const version */
		const byte* begin() const
			MY_ATTRIBUTE((warn_unused_result))
		{
			return(m_data);
		}

		/**
		@return end of used data - const version */
		const byte* end() const
			MY_ATTRIBUTE((warn_unused_result))
		{
			return(begin() + m_used);
		}

	private:
		/**
		@return pointer to start of reserved space */
		template <typename Type>
		Type push(uint32_t size)
		{
			Type	ptr = reinterpret_cast<Type>(end());

			m_used += size;
			ut_ad(m_used <= uint32_t(MAX_DATA_SIZE));

			return(ptr);
		}

		/**
		Grow the stack. */
		void close(const byte* ptr)
		{
			/* Check that it is within bounds */
			ut_ad(ptr >= begin());
			ut_ad(ptr <= begin() + m_buf_end);

			/* We have done the boundary check above */
			m_used = uint32_t(ptr - begin());

			ut_ad(m_used <= MAX_DATA_SIZE);
			ut_d(m_buf_end = 0);
		}

		/**
		Initialise the block */
		void init()
		{
			m_used = 0;
			ut_d(m_buf_end = 0);
			ut_d(m_magic_n = DYN_BLOCK_MAGIC_N);
		}
	private:
#ifdef UNIV_DEBUG
		/** If opened then this is the buffer end offset, else 0 */
		ulint		m_buf_end;

		/** Magic number (DYN_BLOCK_MAGIC_N) */
		ulint		m_magic_n;
#endif /* UNIV_DEBUG */

		/** Storage */
		byte		m_data[MAX_DATA_SIZE];

		/** number of data bytes used in this block */
		uint32_t	m_used;

		friend class mtr_buf_t;
	};

	typedef sized_ilist<block_t> list_t;

	/** Default constructor */
	mtr_buf_t()
		:
		m_heap(),
		m_size()
	{
		push_back(&m_first_block);
	}

	/** Destructor */
	~mtr_buf_t()
	{
		erase();
	}

	/** Reset the buffer vector */
	void erase()
	{
		if (m_heap != NULL) {
			mem_heap_free(m_heap);
			m_heap = NULL;

			/* Initialise the list and add the first block. */
			m_list.clear();
			m_list.push_back(m_first_block);
		} else {
			m_first_block.init();
			ut_ad(m_list.size() == 1);
		}

		m_size = 0;
	}

	/**
	Makes room on top and returns a pointer to a buffer in it. After
	copying the elements, the caller must close the buffer using close().
	@param size	in bytes of the buffer; MUST be <= MAX_DATA_SIZE!
	@return	pointer to the buffer */
	byte* open(ulint size)
		MY_ATTRIBUTE((warn_unused_result))
	{
		ut_ad(size > 0);
		ut_ad(size <= MAX_DATA_SIZE);

		block_t*	block;

		block = has_space(size) ? back() : add_block();

		ut_ad(block->m_used <= MAX_DATA_SIZE);
		ut_d(block->m_buf_end = block->m_used + size);

		return(block->end());
	}

	/**
	Closes the buffer returned by open.
	@param ptr	end of used space */
	void close(const byte* ptr)
	{
		ut_ad(!m_list.empty());
		block_t*	block = back();

		m_size -= block->used();

		block->close(ptr);

		m_size += block->used();
	}

	/**
	Makes room on top and returns a pointer to the added element.
	The caller must copy the element to the pointer returned.
	@param size	in bytes of the element
	@return	pointer to the element */
	template <typename Type>
	Type push(uint32_t size)
	{
		ut_ad(size > 0);
		ut_ad(size <= MAX_DATA_SIZE);

		block_t*	block;

		block = has_space(size) ? back() : add_block();

		m_size += size;

		/* See ISO C++03 14.2/4 for why "template" is required. */

		return(block->template push<Type>(size));
	}

	/**
	Pushes n bytes.
	@param str	string to write
	@param len	string length */
	void push(const byte* ptr, uint32_t len)
	{
		while (len > 0) {
			uint32_t n_copied = std::min(len,
						     uint32_t(MAX_DATA_SIZE));
			::memmove(push<byte*>(n_copied), ptr, n_copied);

			ptr += n_copied;
			len -= n_copied;
		}
	}

	/**
	Returns a pointer to an element in the buffer. const version.
	@param pos	position of element in bytes from start
	@return	pointer to element */
	template <typename Type>
	const Type at(ulint pos) const
	{
		block_t*	block = const_cast<block_t*>(
			const_cast<mtr_buf_t*>(this)->find(pos));

		return(reinterpret_cast<Type>(block->begin() + pos));
	}

	/**
	Returns a pointer to an element in the buffer. non const version.
	@param pos	position of element in bytes from start
	@return	pointer to element */
	template <typename Type>
	Type at(ulint pos)
	{
		block_t*	block = const_cast<block_t*>(find(pos));

		return(reinterpret_cast<Type>(block->begin() + pos));
	}

	/**
	Returns the size of the total stored data.
	@return	data size in bytes */
	ulint size() const
		MY_ATTRIBUTE((warn_unused_result))
	{
#ifdef UNIV_DEBUG
		ulint	total_size = 0;

		for (list_t::iterator it = m_list.begin(), end = m_list.end();
		     it != end; ++it) {
			total_size += it->used();
		}

		ut_ad(total_size == m_size);
#endif /* UNIV_DEBUG */
		return(m_size);
	}

	/**
	Iterate over each block and call the functor.
	@return	false if iteration was terminated. */
	template <typename Functor>
	bool for_each_block(const Functor& functor) const
	{
		for (list_t::iterator it = m_list.begin(), end = m_list.end();
		     it != end; ++it) {

			if (!functor(&*it)) {
				return false;
			}
		}

		return(true);
	}

	/**
	@return the first block */
	block_t* front()
		MY_ATTRIBUTE((warn_unused_result))
	{
		return &m_list.front();
	}

	/**
	@return true if m_first_block block was not filled fully */
	bool is_small() const
		MY_ATTRIBUTE((warn_unused_result))
	{
		return(m_heap == NULL);
	}

	/** @return whether the buffer is empty */
	bool empty() const { return !back()->m_used; }

private:
	// Disable copying
	mtr_buf_t(const mtr_buf_t&);
	mtr_buf_t& operator=(const mtr_buf_t&);

	/**
	Add the block to the end of the list*/
	void push_back(block_t* block)
	{
		block->init();
		m_list.push_back(*block);
	}

	/** @return the last block in the list */
	block_t* back() const
	{
		return &const_cast<block_t&>(m_list.back());
	}

	/*
	@return true if request can be fullfilled */
	bool has_space(ulint size) const
	{
		return(back()->m_used + size <= MAX_DATA_SIZE);
	}

	/*
	@return true if request can be fullfilled */
	bool has_space(ulint size)
	{
		return(back()->m_used + size <= MAX_DATA_SIZE);
	}

	/** Find the block that contains the pos.
	@param pos	absolute offset, it is updated to make it relative
			to the block
	@return the block containing the pos. */
	block_t* find(ulint& pos)
	{
		ut_ad(!m_list.empty());

		for (list_t::iterator it = m_list.begin(), end = m_list.end();
		     it != end; ++it) {

			if (pos < it->used()) {
				ut_ad(it->used() >= pos);

				return &*it;
			}

			pos -= it->used();
		}

		return NULL;
	}

	/**
	Allocate and add a new block to m_list */
	block_t* add_block()
	{
		block_t*	block;

		if (m_heap == NULL) {
			m_heap = mem_heap_create(sizeof(*block));
		}

		block = reinterpret_cast<block_t*>(
			mem_heap_alloc(m_heap, sizeof(*block)));

		push_back(block);

		return(block);
	}

private:
	/** Heap to use for memory allocation */
	mem_heap_t*		m_heap;

	/** Allocated blocks */
	list_t			m_list;

	/** Total size used by all blocks */
	ulint			m_size;

	/** The default block, should always be the first element. This
	is for backwards compatibility and to avoid an extra heap allocation
	for small REDO log records */
	block_t			m_first_block;
};

#endif /* dyn0buf_h */