ClickHouse/contrib/libboost-threadpool/threadpool/scheduling_policies.hpp

/*! \file
* \brief Task scheduling policies.
*
* This file contains some fundamental scheduling policies for the pool class. 
* A scheduling policy is realized by a task container which controls the access to
* the tasks. 	Fundamentally the container determines the order the tasks are processed
* by the thread pool. 
* The task containers need not to be thread-safe because they are used by the pool 
* in thread-safe way. 
*
* Copyright (c) 2005-2007 Philipp Henkel
*
* Use, modification, and distribution are  subject to the
* Boost Software License, Version 1.0. (See accompanying  file
* LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
*
* http://threadpool.sourceforge.net
*
*/


#ifndef THREADPOOL_SCHEDULING_POLICIES_HPP_INCLUDED
#define THREADPOOL_SCHEDULING_POLICIES_HPP_INCLUDED


#include <queue>
#include <deque>

#include "task_adaptors.hpp"

namespace boost { namespace threadpool
{

  /*! \brief SchedulingPolicy which implements FIFO ordering. 
  *
  * This container implements a FIFO scheduling policy.
  * The first task to be added to the scheduler will be the first to be removed.
  * The processing proceeds sequentially in the same order. 
  * FIFO stands for "first in, first out".
  *
  * \param Task A function object which implements the operator()(void).
  *
  */ 
  template <typename Task = task_func>  
  class fifo_scheduler
  {
  public:
    typedef Task task_type; //!< Indicates the scheduler's task type.

  protected:
    std::deque<task_type> m_container;  //!< Internal task container.	


  public:
    /*! Adds a new task to the scheduler.
    * \param task The task object.
    * \return true, if the task could be scheduled and false otherwise. 
    */
    bool push(task_type const & task)
    {
      m_container.push_back(task);
      return true;
    }

    /*! Removes the task which should be executed next.
    */
    void pop()
    {
      m_container.pop_front();
    }

    /*! Gets the task which should be executed next.
    *  \return The task object to be executed.
    */
    task_type const & top() const
    {
      return m_container.front();
    }

    /*! Gets the current number of tasks in the scheduler.
    *  \return The number of tasks.
    *  \remarks Prefer empty() to size() == 0 to check if the scheduler is empty.
    */
    size_t size() const
    {
      return m_container.size();
    }

    /*! Checks if the scheduler is empty.
    *  \return true if the scheduler contains no tasks, false otherwise.
    *  \remarks Is more efficient than size() == 0. 
    */
    bool empty() const
    {
      return m_container.empty();
    }

    /*! Removes all tasks from the scheduler.
    */  
    void clear()
    {   
      m_container.clear();
    } 
  };



  /*! \brief SchedulingPolicy which implements LIFO ordering. 
  *
  * This container implements a LIFO scheduling policy.
  * The last task to be added to the scheduler will be the first to be removed.
  * LIFO stands for "last in, first out".
  *
  * \param Task A function object which implements the operator()(void).
  *
  */ 
  template <typename Task = task_func>  
  class lifo_scheduler
  {
  public:
    typedef Task task_type;  //!< Indicates the scheduler's task type.

  protected:
    std::deque<task_type> m_container;  //!< Internal task container.	

  public:
    /*! Adds a new task to the scheduler.
    * \param task The task object.
    * \return true, if the task could be scheduled and false otherwise. 
    */
    bool push(task_type const & task)
    {
      m_container.push_front(task);
      return true;
    }

    /*! Removes the task which should be executed next.
    */
    void pop()
    {
      m_container.pop_front();
    }

    /*! Gets the task which should be executed next.
    *  \return The task object to be executed.
    */
    task_type const & top() const
    {
      return m_container.front();
    }

    /*! Gets the current number of tasks in the scheduler.
    *  \return The number of tasks.
    *  \remarks Prefer empty() to size() == 0 to check if the scheduler is empty.
    */
    size_t size() const
    {
      return m_container.size();
    }

    /*! Checks if the scheduler is empty.
    *  \return true if the scheduler contains no tasks, false otherwise.
    *  \remarks Is more efficient than size() == 0. 
    */
    bool empty() const
    {
      return m_container.empty();
    }

    /*! Removes all tasks from the scheduler.
    */  
    void clear()
    {    
      m_container.clear();
    } 

  };



  /*! \brief SchedulingPolicy which implements prioritized ordering. 
  *
  * This container implements a scheduling policy based on task priorities.
  * The task with highest priority will be the first to be removed.
  * It must be possible to compare two tasks using operator<. 
  *
  * \param Task A function object which implements the operator() and operator<. operator< must be a partial ordering.
  *
  * \see prio_thread_func
  *
  */ 
  template <typename Task = prio_task_func>  
  class prio_scheduler
  {
  public:
    typedef Task task_type; //!< Indicates the scheduler's task type.

  protected:
    std::priority_queue<task_type> m_container;  //!< Internal task container.


  public:
    /*! Adds a new task to the scheduler.
    * \param task The task object.
    * \return true, if the task could be scheduled and false otherwise. 
    */
    bool push(task_type const & task)
    {
      m_container.push(task);
      return true;
    }

    /*! Removes the task which should be executed next.
    */
    void pop()
    {
      m_container.pop();
    }

    /*! Gets the task which should be executed next.
    *  \return The task object to be executed.
    */
    task_type const & top() const
    {
      return m_container.top();
    }

    /*! Gets the current number of tasks in the scheduler.
    *  \return The number of tasks.
    *  \remarks Prefer empty() to size() == 0 to check if the scheduler is empty.
    */
    size_t size() const
    {
      return m_container.size();
    }

    /*! Checks if the scheduler is empty.
    *  \return true if the scheduler contains no tasks, false otherwise.
    *  \remarks Is more efficient than size() == 0. 
    */
    bool empty() const
    {
      return m_container.empty();
    }

    /*! Removes all tasks from the scheduler.
    */  
    void clear()
    {    
      while(!m_container.empty())
      {
        m_container.pop();
      }
    } 
  };


} } // namespace boost::threadpool


#endif // THREADPOOL_SCHEDULING_POLICIES_HPP_INCLUDED