/*****************************************************************************
Copyright (c) 2020 MariaDB Corporation.

This program is free software; you can redistribute it and/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 02110-1335 USA

*****************************************************************************/

#include <atomic>
#include <thread>
#include <log0types.h>

struct group_commit_waiter_t;

/**
Special synchronization primitive, which is helpful for
performing group commit.

It has a state consisting of
 - locked (bool)
 - current value (number). This value is always increasing.
 - pending value (number). current value can soon become this number
   This is only used for optimization, does not have to be exact

Operations supported on this semaphore

1.acquire(num):
- waits until current value exceeds num, or until lock is granted.

- returns EXPIRED if current_value >= num,
  or ACQUIRED, if current_value < num and lock is granted.

2.release(num)
- releases lock
- sets new current value to max(num,current_value)
- releases some threads waiting in acquire()

3. value()
- read current value

4. pending_value()
- read pending value

5. set_pending_value()
*/
class group_commit_lock
{
  using value_type = lsn_t;
#ifndef DBUG_OFF
  std::thread::id m_owner_id{};
#endif
  std::mutex m_mtx;
  std::atomic<value_type> m_value;
  std::atomic<value_type> m_pending_value;
  bool m_lock;
  group_commit_waiter_t* m_waiters_list;
public:
  group_commit_lock();
  enum lock_return_code
  {
    ACQUIRED,
    EXPIRED
  };
  lock_return_code acquire(value_type num);
  void release(value_type num);
  value_type value() const;
  value_type pending() const;
  void set_pending(value_type num);
#ifndef DBUG_OFF
  bool is_owner();
#endif
};