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/*****************************************************************************
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
};
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