dyn0buf.h

Go to the documentation of this file.

/*****************************************************************************
 
Copyright (c) 2013, 2024, Oracle and/or its affiliates.
 
This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License, version 2.0, as published by the
Free Software Foundation.
 
This program is designed to work with certain software (including
but not limited to OpenSSL) that is licensed under separate terms,
as designated in a particular file or component or in included license
documentation.  The authors of MySQL hereby grant you an additional
permission to link the program and your derivative works with the
separately licensed software that they have either included with
the program or referenced in the documentation.
 
This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License, version 2.0,
for more details.
 
You should have received a copy of the GNU General Public License along with
this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA
 
*****************************************************************************/
 
/** @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 */