sql_backup_lock.h

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/* Copyright (c) 2017, 2025, 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 designed to work 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 either included with
   the program or referenced in the documentation.
 
   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 SQL_LOCK_INCLUDED
#define SQL_LOCK_INCLUDED
 
#include <sys/types.h>
 
#include "my_sqlcommand.h"  // SQLCOM_LOCK_INSTANCE, SQLCOM_UNLOCK_INSTANCE
#include "sql/sql_cmd.h"    // Sql_cmd
 
class THD;
 
/**
  Sql_cmd_lock_instance represents statement LOCK INSTANCE FOR BACKUP.
*/
 
class Sql_cmd_lock_instance : public Sql_cmd {
 public:
  /**
    Execute LOCK INSTANCE statement once.
 
    @param thd Thread handler
 
    @returns false on success, true on error
  */
 
  bool execute(THD *thd) override;
 
  enum_sql_command sql_command_code() const override {
    return SQLCOM_LOCK_INSTANCE;
  }
};
 
/**
  Sql_cmd_unlock_instance represents statement UNLOCK INSTANCE.
*/
 
class Sql_cmd_unlock_instance : public Sql_cmd {
 public:
  /**
    Execute UNLOCK INSTANCE statement once.
 
    @param thd Thread handler
 
    @returns false on success, true on error
  */
 
  bool execute(THD *thd) override;
 
  enum_sql_command sql_command_code() const override {
    return SQLCOM_UNLOCK_INSTANCE;
  }
};
 
/**
   MDL_key::BACKUP_LOCK RAII.
 */
class Shared_backup_lock_guard {
 public:
  /**
    There are three possible results while checking if the instance is locked
    for backup.
  */
  enum class Lock_result { not_locked = 0, locked = 1, oom = 2 };
 
  Shared_backup_lock_guard(THD *thd);
  Shared_backup_lock_guard(const Shared_backup_lock_guard &o) = delete;
  Shared_backup_lock_guard(Shared_backup_lock_guard &&o) = default;
  Shared_backup_lock_guard &operator=(const Shared_backup_lock_guard &o) =
      delete;
  Shared_backup_lock_guard &operator=(Shared_backup_lock_guard &&o) = default;
 
  ~Shared_backup_lock_guard();
 
  operator Lock_result() const;
 
 private:
  /**
    Try to acquire shared backup lock.
 
    @param[in] thd                Current thread context
    @param[in] for_trx            true if MDL duration is MDL_TRANSACTION
                                  false if MDL duration is MDL_EXPLICIT
 
    @return Operation status.
      @retval Shared_backup_lock_guard::Lock_result::locked       Locked shared
    BACKUP lock.
      @retval Shared_backup_lock_guard::Lock_result::not_locked   Could not lock
    shared BACKUP lock. Conflicting lock exists.
      @retval Shared_backup_lock_guard::Lock_result::oom          Error. Could
    not lock shared BACKUP lock.
  */
  Shared_backup_lock_guard::Lock_result try_acquire_shared_backup_lock(
      THD *thd, bool for_trx);
  Shared_backup_lock_guard::Lock_result m_lock_state;
  THD *m_thd;
};
 
/**
  Acquire exclusive Backup Lock.
 
  @param[in] thd                Current thread context
  @param[in] lock_wait_timeout  How many seconds to wait before timeout.
  @param[in] for_trx            true if MDL duration is MDL_TRANSACTION
                                false if MDL duration is MDL_EXPLICIT
 
  @return Operation status.
    @retval false Success
    @retval true  Failure
*/
 
bool acquire_exclusive_backup_lock(THD *thd, unsigned long lock_wait_timeout,
                                   bool for_trx);
 
/**
  Acquire shared Backup Lock.
 
  @param[in] thd                Current thread context
  @param[in] lock_wait_timeout  How many seconds to wait before timeout.
  @param[in] for_trx            true if MDL duration is MDL_TRANSACTION
                                false if MDL duration is MDL_EXPLICIT
 
  @return Operation status.
    @retval false Success
    @retval true  Failure
*/
 
bool acquire_shared_backup_lock(THD *thd, unsigned long lock_wait_timeout,
                                bool for_trx = true);
 
/**
  Release Backup Lock if it was acquired.
 
  @param[in] thd         Current thread context
*/
 
void release_backup_lock(THD *thd);
 
#endif /* SQL_LOCK_INCLUDED */