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/* Copyright (c) 2018, 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 MDL_CONTEXT_BACKUP_H
#define MDL_CONTEXT_BACKUP_H
#include <cstring>
#include <map>
#include <memory>
#include "my_char_traits.h"
#include "sql/malloc_allocator.h"
#include "sql/mdl.h"
/**
Class which is used to store MDL locks associated with XA transactions
in prepared state which clients have disconnected. These locks are not
associated with any particular THD/thread. Later they will be retrieved
by the thread which attempts to process the prepared XA transaction.
This is singleton class. It contains map where each element represents
MDL_context of disconnected prepared XA transaction and holds related
metadata locks.
*/
class MDL_context_backup_manager {
private:
/**
Key for uniquely identifying MDL_context in the MDL_context_backup map.
*/
using MDL_context_backup_key =
std::basic_string<uchar, my_char_traits<uchar>>;
class MDL_context_backup;
typedef std::map<
MDL_context_backup_key, std::unique_ptr<MDL_context_backup>,
std::less<MDL_context_backup_key>,
Malloc_allocator<std::pair<const MDL_context_backup_key,
std::unique_ptr<MDL_context_backup>>>>
Element_map_type; // Real map type.
/* Singleton. No explicit Objects */
MDL_context_backup_manager(PSI_memory_key key);
/* Singleton Object */
static MDL_context_backup_manager *m_single;
public:
/* Not copyable. */
MDL_context_backup_manager(const MDL_context_backup_manager &) = delete;
/* Not assignable. */
void operator=(const MDL_context_backup_manager &) = delete;
/**
Initialize member variables and singleton object
*/
static bool init();
/**
Return singleton object
*/
static MDL_context_backup_manager &instance();
/**
Cleanup and delete singleton object
*/
static void destroy();
private:
/**
destroy mutex and clear backup map
*/
~MDL_context_backup_manager();
static void init_psi_keys(void);
public:
/**
Create backup from given MDL_context by cloning all transactional
locks to backup context and adds to backup context manager collection.
This method is used during user's session disconnect for storing MDL
locks acquired by prepared XA transaction(s).
This function does not set error codes beyond what is set by the
functions it calls.
@param[in] context MDL_context from which backup is created.
@param[in] key Key to identity MDL_context
@param[in] keylen Key Length
@retval true Error, e.g. Fail to create backup object, fail
to clone locks.
@retval false Success or a backup already exist for this key.
*/
bool create_backup(const MDL_context *context, const uchar *key,
const size_t keylen);
/**
Create backup MDL_context, process request on it and add to backup context
manager collection. This method is called during server start up in order
to acquire MDL locks held by prepared XA transactions existed before server
shutdown.
This function does not set error codes beyond what is set by the
functions it calls.
@param[in] mdl_requests Requests need to be processed and backed up.
@param[in] key Key to identity MDL_context
@param[in] keylen Key Length
@retval true Error, e.g. Fail to create backup object, fail
to clone locks.
@retval false Success or a backup already exist for this key.
*/
bool create_backup(MDL_request_list *mdl_requests, const uchar *key,
const size_t keylen);
/**
Restore locks from backup to given MDL_context.
This function does not set error codes beyond what is set by the
functions it calls.
@param[out] mdl_context MDL_context to which backup is restored.
@param[in] key Key to identity MDL_context
@param[in] keylen Key Length
@retval true Error, e.g. There is no element in the
collection matching given key, fail
to restore locks.
@retval false Success
*/
bool restore_backup(MDL_context *mdl_context, const uchar *key,
const size_t keylen);
/**
Delete backup context and release associated locks.
@param[in] key Key to identity MDL_context
@param[in] keylen Key Length
*/
void delete_backup(const uchar *key, const size_t keylen);
private:
// Collection for holding MDL_context_backup elements
Element_map_type m_backup_map;
// Mutex to protect m_backup_map
mysql_mutex_t m_LOCK_mdl_context_backup;
/**
Check for presence of a record with specified key
@param[in] key_obj Key to identity MDL_context
@return true if there is a record for specified key, else false
*/
bool check_key_exist(const MDL_context_backup_key &key_obj);
};
#endif // MDL_CONTEXT_BACKUP_H
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