1 files changed, 81 insertions, 0 deletions
diff --git a/storage/innobase/log/log0sync.h b/storage/innobase/log/log0sync.h
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+++ b/storage/innobase/log/log0sync.h
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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
+};