/*
 * Copyright (c) 2015, 2021, 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 also distributed 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 included with MySQL.
 *
 * 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
 */

#ifndef _NGS_SCHEDULER_H_
#define _NGS_SCHEDULER_H_

#include "ngs/thread.h"
#include "ngs/memory.h"
#include "ngs_common/atomic.h"
#include <string>
#include <vector>
#include <list>


namespace ngs
{
  // Scheduler with dynamic thread pool.
  class Scheduler_dynamic
  {
  public:
    class Monitor_interface
    {
    public:
      virtual ~Monitor_interface() {}

      virtual void on_worker_thread_create() = 0;
      virtual void on_worker_thread_destroy() = 0;
      virtual void on_task_start() = 0;
      virtual void on_task_end() = 0;
    };

    typedef ngs::function<void()> Task;

    Scheduler_dynamic(const char* name, PSI_thread_key thread_key = PSI_NOT_INSTRUMENTED);
    virtual ~Scheduler_dynamic();

    virtual void launch();
    virtual void stop();
    virtual unsigned int set_num_workers(unsigned int n);
    void set_idle_worker_timeout(unsigned long long milliseconds);
    bool post(Task* task);
    bool post(const Task& task);
    bool post_and_wait(const Task& task);

    virtual bool thread_init() { return true; }
    virtual void thread_end();

    void set_monitor(Monitor_interface *monitor);

    bool is_worker_thread(my_thread_t thread_id);
    bool is_running();
    void join_terminating_workers();

  private:
    template<typename Element_type>
    class lock_list
    {
    public:
      lock_list()
      : m_access_mutex(KEY_mutex_x_lock_list_access)
      {
      }

      bool empty()
      {
        Mutex_lock guard(m_access_mutex);
        return m_list.empty();
      }

      bool push(const Element_type &t)
      {
        Mutex_lock guard(m_access_mutex);
        m_list.push_back(t);
        return true;
      }

      bool pop(Element_type &result)
      {
        Mutex_lock guard(m_access_mutex);
        if (m_list.empty())
          return false;

        result = m_list.front();

        m_list.pop_front();
        return true;
      }

      bool remove_if(Element_type &result, ngs::function<bool(Element_type &)> matches)
      {
        Mutex_lock guard(m_access_mutex);
        for (typename std::list<Element_type>::iterator it = m_list.begin(); it != m_list.end(); ++it)
        {
          if (matches(*it))
          {
            result = *it;
            m_list.erase(it);
            return true;
          }
        }

        return false;
      }

    private:
      Mutex m_access_mutex;
      std::list<Element_type> m_list;
    };

    Scheduler_dynamic(const Scheduler_dynamic&);
    Scheduler_dynamic& operator=(const Scheduler_dynamic&);

    static void* worker_proxy(void* data);
    void* worker();

    void create_thread();
    void create_min_num_workers();

    static bool thread_id_matches(Thread_t& thread, my_thread_t id)
    {
      return thread.thread == id;
    }

    bool wait_if_idle_then_delete_worker(ulonglong &thread_waiting_started);
    int32 increase_workers_count();
    int32 decrease_workers_count();
    int32 increase_tasks_count();
    int32 decrease_tasks_count();

    const std::string m_name;
    Mutex m_worker_pending_mutex;
    Cond m_worker_pending_cond;
    Mutex m_thread_exit_mutex;
    Cond m_thread_exit_cond;
    Mutex m_post_mutex;
    volatile ngs::atomic<int32> m_is_running;
    volatile ngs::atomic<int32> m_min_workers_count;
    volatile ngs::atomic<int32> m_workers_count;
    volatile ngs::atomic<int32> m_tasks_count;
    volatile ngs::atomic<int64> m_idle_worker_timeout; // milliseconds
    lock_list<Task *> m_tasks;
    lock_list<Thread_t> m_threads;
    lock_list<my_thread_t> m_terminating_workers;
    ngs::Memory_instrumented<Monitor_interface>::Unique_ptr m_monitor;
    PSI_thread_key m_thread_key;
  };
}

#endif
