mariadb/tpool/tpool_structs.h

/* Copyright(C) 2019 MariaDB Corporation

This program is free software; you can redistribute itand /or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.

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 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 Street, Fifth Floor, Boston, MA 02111 - 1301 USA*/

#pragma once
#include <vector>
#include <stack>
#include <mutex>
#include <condition_variable>
#include <assert.h>
#include <algorithm>

namespace tpool
{

enum cache_notification_mode
{
  NOTIFY_ONE,
  NOTIFY_ALL
};

/**
  Generic "pointer" cache of a fixed size
  with fast put/get operations.

  Compared to STL containers, is faster/does not
  do allocations. However, put() operation will wait
  if there is no free items.
*/
template<typename T> class cache
{
  std::mutex m_mtx;
  std::condition_variable m_cv;
  std::vector<T>  m_base;
  std::vector<T*> m_cache;
  cache_notification_mode m_notification_mode;
  int m_waiters;

  bool is_full()
  {
    return m_cache.size() == m_base.size();
  }

public:
  cache(size_t count, cache_notification_mode mode= tpool::cache_notification_mode::NOTIFY_ALL):
  m_mtx(), m_cv(), m_base(count),m_cache(count), m_notification_mode(mode),m_waiters()
  {
    for(size_t i = 0 ; i < count; i++)
      m_cache[i]=&m_base[i];
  }

  T* get(bool blocking=true)
  {
    std::unique_lock<std::mutex> lk(m_mtx);
    if (blocking)
    {
      while(m_cache.empty())
        m_cv.wait(lk);
    }
    else
    {
      if(m_cache.empty())
        return nullptr;
    }
    T* ret = m_cache.back();
    m_cache.pop_back();
    return ret;
  }


  void put(T *ele)
  {
    std::unique_lock<std::mutex> lk(m_mtx);
    m_cache.push_back(ele);
    if (m_notification_mode == NOTIFY_ONE)
      m_cv.notify_one();
    else if(m_cache.size() == 1)
      m_cv.notify_all(); // Signal cache is not empty
    else if(m_waiters && is_full())
      m_cv.notify_all(); // Signal cache is full
  }

  bool contains(T* ele)
  {
    return ele >= &m_base[0] && ele <= &m_base[m_base.size() -1];
  }

  /* Wait until cache is full.*/
  void wait()
  {
    std::unique_lock<std::mutex> lk(m_mtx);
    m_waiters++;
    while(!is_full())
      m_cv.wait(lk);
    m_waiters--;
  }

  size_t size()
  {
    return m_cache.size();
  }
};


/**
  Circular, fixed size queue
  used for the task queue.

  Compared to STL queue, this one is
  faster, and does not do memory allocations
*/
template <typename T> class circular_queue
{

public:
  circular_queue(size_t N = 16)
    : m_capacity(N + 1), m_buffer(m_capacity), m_head(), m_tail()
  {
  }
  bool empty() { return m_head == m_tail; }
  bool full() { return (m_head + 1) % m_capacity == m_tail; }
  void clear() { m_head = m_tail = 0; }
  void resize(size_t new_size)
  {
    auto current_size = size();
    if (new_size <= current_size)
      return;
    size_t new_capacity = new_size - 1;
    std::vector<T> new_buffer(new_capacity);
    /* Figure out faster way to copy*/
    size_t i = 0;
    while (!empty())
    {
      T& ele = front();
      pop();
      new_buffer[i++] = ele;
    }
    m_buffer = new_buffer;
    m_capacity = new_capacity;
    m_tail = 0;
    m_head = current_size;
  }
  void push(T ele)
  {
    if (full())
    {
      assert(size() == m_capacity - 1);
      resize(size() + 1024);
    }
    m_buffer[m_head] = ele;
    m_head = (m_head + 1) % m_capacity;
  }
  void push_front(T ele)
  {
    if (full())
    {
      resize(size() + 1024);
    }
    if (m_tail == 0)
      m_tail = m_capacity - 1;
    else
      m_tail--;
    m_buffer[m_tail] = ele;
  }
  T& front()
  {
    assert(!empty());
    return m_buffer[m_tail];
  }
  void pop()
  {
    assert(!empty());
    m_tail = (m_tail + 1) % m_capacity;
  }
  size_t size()
  {
    if (m_head < m_tail)
    {
      return m_capacity - m_tail + m_head;
    }
    else
    {
      return m_head - m_tail;
    }
  }

  /*Iterator over elements in queue.*/
  class iterator
  {
    size_t m_pos;
    circular_queue<T>* m_queue;
  public:
    explicit iterator(size_t pos , circular_queue<T>* q) : m_pos(pos), m_queue(q) {}
    iterator& operator++()
    {
      m_pos= (m_pos + 1) % m_queue->m_capacity;
      return *this;
    }
    iterator operator++(int)
    {
      iterator retval= *this;
      ++*this;
      return retval;
    }
    bool operator==(iterator other) const { return m_pos == other.m_pos; }
    bool operator!=(iterator other) const { return !(*this == other); }
    T& operator*() const { return m_queue->m_buffer[m_pos]; }
  };

  iterator begin() { return iterator(m_tail, this); }
  iterator end() { return iterator(m_head, this); }
private:
  size_t m_capacity;
  std::vector<T> m_buffer;
  size_t m_head;
  size_t m_tail;
};

/* Doubly linked list. Intrusive,
   requires element to have m_next and m_prev pointers.
*/
template<typename T> class doubly_linked_list
{
public:
  T* m_first;
  T* m_last;
  size_t m_count;
  doubly_linked_list():m_first(),m_last(),m_count()
  {}
  void check()
  {
    assert(!m_first || !m_first->m_prev);
    assert(!m_last || !m_last->m_next);
    assert((!m_first && !m_last && m_count == 0)
     || (m_first != 0 && m_last != 0 && m_count > 0));
    T* current = m_first;
    for(size_t i=1; i< m_count;i++)
    {
      current = current->m_next;
    }
    assert(current == m_last);
    current = m_last;
    for (size_t i = 1; i < m_count; i++)
    {
      current = current->m_prev;
    }
    assert(current == m_first);
  }
  T* front()
  {
    return m_first;
  }
  size_t size()
  {
    return m_count;
  }
  void push_back(T* ele)
  {
    ele->m_prev = m_last;
    if (m_last)
      m_last->m_next = ele;

    ele->m_next = 0;
    m_last = ele;
    if (!m_first)
      m_first = m_last;

    m_count++;
  }
  T* back()
  {
    return m_last;
  }
  bool empty()
  {
    return m_count == 0;
  }
  void pop_back()
  {
    m_last = m_last->m_prev;
    if (m_last)
      m_last->m_next = 0;
    else
      m_first = 0;
    m_count--;
  }
  bool contains(T* ele)
  {
    if (!ele)
      return false;
    T* current = m_first;
    while(current)
    {
      if(current == ele)
        return true;
      current = current->m_next;
    }
    return false;
  }

  void erase(T* ele)
  {
    assert(contains(ele));

    if (ele == m_first)
    {
      m_first = ele->m_next;
      if (m_first)
        m_first->m_prev = 0;
      else
        m_last = 0;
    }
    else if (ele == m_last)
    {
      assert(ele->m_prev);
      m_last = ele->m_prev;
      m_last->m_next = 0;
    }
    else
    {
      assert(ele->m_next);
      assert(ele->m_prev);
      ele->m_next->m_prev = ele->m_prev;
      ele->m_prev->m_next = ele->m_next;
    }
    m_count--;
  }
};

}