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 "dyn0types.h"
#include "mem0mem.h"
#include "univ.i"
#include "ut0lst.h"
 
/** Class that manages dynamic buffers. It uses a UT_LIST of
dyn_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. */
template <size_t SIZE = DYN_ARRAY_DATA_SIZE>
class dyn_buf_t {
 public:
  class block_t;
 
  typedef UT_LIST_NODE_T(block_t) block_node_t;
 
  class block_t {
   public:
    block_t() {
      static_assert(MAX_DATA_SIZE <= (2 << 15));
      init();
    }
 
    ~block_t() = default;
 
    /**
    Gets the number of used bytes in a block.
    @return     number of bytes used */
    [[nodiscard]] ulint used() const {
      return (static_cast<ulint>(m_used & ~DYN_BLOCK_FULL_FLAG));
    }
 
    /**
    Gets pointer to the start of data.
    @return     pointer to data */
    [[nodiscard]] byte *start() { return (m_data); }
 
    /**
    @return start of data - non const version */
    [[nodiscard]] byte *begin() { return (m_data); }
 
    /**
    @return end of used data - non const version */
    [[nodiscard]] byte *end() { return (begin() + m_used); }
 
    /**
    @return start of data - const version */
    [[nodiscard]] const byte *begin() const { return (m_data); }
 
    /**
    @return end of used data - const version */
    [[nodiscard]] const byte *end() const { 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 <= static_cast<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 = static_cast<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 */
 
    /** SIZE - sizeof(m_node) + sizeof(m_used) */
    static constexpr auto MAX_DATA_SIZE = SIZE;
 
    /** Storage */
    byte m_data[MAX_DATA_SIZE];
 
    /** Doubly linked list node. */
    block_node_t m_node;
 
    /** number of data bytes used in this block;
    DYN_BLOCK_FULL_FLAG is set when the block becomes full */
    uint32_t m_used;
 
    friend class dyn_buf_t;
  };
  typedef UT_LIST_BASE_NODE_T(block_t, m_node) block_list_t;
 
  static constexpr auto MAX_DATA_SIZE = block_t::MAX_DATA_SIZE;
 
  /** Default constructor */
  dyn_buf_t() : m_heap(), m_list(), m_size() { push_back(&m_first_block); }
 
  /** Destructor */
  ~dyn_buf_t() { erase(); }
 
  /** Reset the buffer vector */
  void erase() {
    if (m_heap != nullptr) {
      mem_heap_free(m_heap);
      m_heap = nullptr;
 
      /* Initialise the list and add the first block. */
      m_list.clear();
      push_back(&m_first_block);
    } else {
      m_first_block.init();
      ut_ad(UT_LIST_GET_LEN(m_list) == 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 */
  [[nodiscard]] byte *open(ulint size) {
    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(UT_LIST_GET_LEN(m_list) > 0);
    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        ptr     string to write
  @param        len     string length */
  void push(const byte *ptr, uint32_t len) {
    while (len > 0) {
      uint32_t n_copied;
 
      if (len >= MAX_DATA_SIZE) {
        n_copied = MAX_DATA_SIZE;
      } else {
        n_copied = len;
      }
 
      ::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<dyn_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 */
  [[nodiscard]] ulint size() const {
#ifdef UNIV_DEBUG
    ulint total_size = 0;
 
    for (const block_t *block : m_list) {
      total_size += block->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(Functor &functor) const {
    for (const block_t *block : m_list) {
      if (!functor(block)) {
        return (false);
      }
    }
 
    return (true);
  }
 
  /**
  Iterate over all the blocks in reverse and call the iterator
  @return       false if iteration was terminated. */
  template <typename Functor>
  bool for_each_block_in_reverse(Functor &functor) const {
    for (block_t *block = UT_LIST_GET_LAST(m_list); block != nullptr;
         block = UT_LIST_GET_PREV(m_node, block)) {
      if (!functor(block)) {
        return (false);
      }
    }
 
    return (true);
  }
 
  /**
  @return the first block */
  [[nodiscard]] block_t *front() {
    ut_ad(UT_LIST_GET_LEN(m_list) > 0);
    return (UT_LIST_GET_FIRST(m_list));
  }
 
  /**
  @return true if m_first_block block was not filled fully */
  [[nodiscard]] bool is_small() const { return (m_heap == nullptr); }
 
 private:
  // Disable copying
  dyn_buf_t(dyn_buf_t &&) = delete;
  dyn_buf_t(const dyn_buf_t &) = delete;
  dyn_buf_t &operator=(dyn_buf_t &&) = delete;
  dyn_buf_t &operator=(const dyn_buf_t &) = delete;
 
  /**
  Add the block to the end of the list*/
  void push_back(block_t *block) {
    block->init();
 
    UT_LIST_ADD_LAST(m_list, block);
  }
 
  /** @return the last block in the list */
  block_t *back() { return (UT_LIST_GET_LAST(m_list)); }
 
  /*
  @return true if request can be fulfilled */
  bool has_space(ulint size) const {
    return (back()->m_used + size <= MAX_DATA_SIZE);
  }
 
  /*
  @return true if request can be fulfilled */
  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(UT_LIST_GET_LEN(m_list) > 0);
 
    for (auto block : m_list) {
      if (pos < block->used()) {
        return block;
      }
 
      pos -= block->used();
    }
 
    ut_d(ut_error);
    ut_o(return nullptr);
  }
 
  /**
  Allocate and add a new block to m_list */
  block_t *add_block() {
    block_t *block;
 
    if (m_heap == nullptr) {
      m_heap = mem_heap_create(sizeof(*block), UT_LOCATION_HERE);
    }
 
    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 */
  block_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;
};
 
typedef dyn_buf_t<DYN_ARRAY_DATA_SIZE> mtr_buf_t;
 
/** mtr_buf_t copier */
struct mtr_buf_copy_t {
  /** The copied buffer */
  mtr_buf_t m_buf;
 
  /** Append a block to the redo log buffer.
  @return whether the appending should continue (always true here) */
  bool operator()(const mtr_buf_t::block_t *block) {
    byte *buf = m_buf.open(block->used());
    memcpy(buf, block->begin(), block->used());
    m_buf.close(buf + block->used());
    return (true);
  }
};
 
#endif /* dyn0buf_h */