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/*****************************************************************************
Copyright (c) 1997, 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
*****************************************************************************/
/** @file include/read0read.h
Cursor read
Created 2/16/1997 Heikki Tuuri
*******************************************************/
#ifndef read0read_h
#define read0read_h
#include <stddef.h>
#include <algorithm>
#include "read0types.h"
#include "univ.i"
/** The MVCC read view manager */
class MVCC {
public:
/** Constructor
@param size Number of views to pre-allocate */
explicit MVCC(ulint size);
/** Destructor.
Free all the views in the m_free list */
~MVCC();
/** Allocate and create a view.
@param view View owned by this class created for the caller. Must be
freed by calling view_close()
@param trx Transaction instance of caller */
void view_open(ReadView *&view, trx_t *trx);
/**
Close a view created by the above function.
@param view view allocated by trx_open.
@param own_mutex true if caller owns trx_sys_t::mutex */
void view_close(ReadView *&view, bool own_mutex);
/**
Release a view that is inactive but not closed. Caller must own
the trx_sys_t::mutex.
@param view View to release */
void view_release(ReadView *&view);
/** Clones the oldest view and stores it in view. No need to
call view_close(). The caller owns the view that is passed in.
It will also move the closed views from the m_views list to the
m_free list. This function is called by Purge to determine whether it should
purge the delete marked record or not.
@param view Preallocated view, owned by the caller */
void clone_oldest_view(ReadView *view);
/**
@return the number of active views */
ulint size() const;
/**
@return true if the view is active and valid */
static bool is_view_active(ReadView *view) {
ut_a(view != reinterpret_cast<ReadView *>(0x1));
return (view != nullptr && !(intptr_t(view) & 0x1));
}
/**
Set the view creator transaction id. Note: This should be set only
for views created by RW transactions.
@param view Set the creator trx id for this view
@param id Transaction id to set */
static void set_view_creator_trx_id(ReadView *view, trx_id_t id) {
ut_ad(id > 0);
view->creator_trx_id(id);
}
private:
/**
Validates a read view list. */
bool validate() const;
/**
Find a free view from the active list, if none found then allocate
a new view. This function will also attempt to move delete marked
views from the active list to the freed list.
@return a view to use */
inline ReadView *get_view();
/**
Get the oldest view in the system. It will also move the delete
marked read views from the views list to the freed list.
@return oldest view if found or NULL */
inline ReadView *get_oldest_view() const;
ReadView *get_view_created_by_trx_id(trx_id_t trx_id) const;
private:
// Prevent copying
MVCC(const MVCC &);
MVCC &operator=(const MVCC &);
private:
typedef UT_LIST_BASE_NODE_T(ReadView, m_view_list) view_list_t;
/** Free views ready for reuse. */
view_list_t m_free;
/** Active and closed views, the closed views will have the
creator trx id set to TRX_ID_MAX */
view_list_t m_views;
};
#endif /* read0read_h */
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