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d8b8258a53
Retry write and/or flush, if group_commit_lock::release() indicates that there are async waiters left, and there is no new group commit lead
99 lines
2.8 KiB
C++
99 lines
2.8 KiB
C++
/*****************************************************************************
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Copyright (c) 2020 MariaDB Corporation.
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This program is free software; you can redistribute it and/or modify it under
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the terms of the GNU General Public License as published by the Free Software
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Foundation; version 2 of the License.
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This program is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
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You should have received a copy of the GNU General Public License along with
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this program; if not, write to the Free Software Foundation, Inc.,
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51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA
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*****************************************************************************/
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#include <atomic>
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#include <thread>
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#include <log0types.h>
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#include <vector>
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struct group_commit_waiter_t;
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struct completion_callback
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{
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void (*m_callback)(void*);
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void* m_param;
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};
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/**
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Special synchronization primitive, which is helpful for
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performing group commit.
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It has a state consisting of
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- locked (bool)
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- current value (number). This value is always increasing.
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- pending value (number). current value can soon become this number
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This is only used for optimization, does not have to be exact
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Operations supported on this semaphore
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1.acquire(num, callback):
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- waits until current value exceeds num, or until lock is granted.
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if running synchronously (callback is nullptr)
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- returns EXPIRED if current_value >= num,
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or ACQUIRED, if current_value < num and lock is granted,
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or CALLBACK_QUEUED, if callback was not nullptr, and function
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would otherwise have to wait
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2.release(num)
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- releases lock
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- sets new current value to max(num,current_value)
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- releases some threads waiting in acquire()
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- executes some callbacks
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- might return some lsn, meaning there are some pending
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callbacks left, and there is no new group commit lead
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(i.e caller must do something to flush those pending callbacks)
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3. value()
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- read current value
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4. pending_value()
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- read pending value
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5. set_pending_value()
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*/
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class group_commit_lock
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{
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using value_type = lsn_t;
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#ifndef DBUG_OFF
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std::thread::id m_owner_id{};
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#endif
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std::mutex m_mtx;
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std::atomic<value_type> m_value;
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std::atomic<value_type> m_pending_value;
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bool m_lock;
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group_commit_waiter_t* m_waiters_list;
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typedef std::pair<value_type, completion_callback> pending_cb;
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std::vector<pending_cb> m_pending_callbacks;
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public:
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group_commit_lock();
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enum lock_return_code
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{
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ACQUIRED,
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EXPIRED,
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CALLBACK_QUEUED
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};
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lock_return_code acquire(value_type num, const completion_callback *cb);
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value_type release(value_type num);
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value_type value() const;
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value_type pending() const;
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void set_pending(value_type num);
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#ifndef DBUG_OFF
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bool is_owner();
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#endif
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};
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