Zabbix

/*

** Copyright (C) 2001-2025 Zabbix SIA

**

** This program is free software: you can redistribute it and/or modify it under the terms of

** the GNU Affero General Public License as published by the Free Software Foundation, version 3.

**

** 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 Affero General Public License for more details.

**

** You should have received a copy of the GNU Affero General Public License along with this program.

** If not, see <https://www.gnu.org/licenses/>.

**/

​

#ifndef ZABBIX_CACHEVALUE_H

#define ZABBIX_CACHEVALUE_H

​

#include "zbxtypes.h"

#include "zbxalgo.h"

#include "zbxhistory.h"

#include "zbxshmem.h"

​

/*

 * The Value Cache provides read caching of item historical data residing in history

 * tables. No components must read history tables manually. Instead all history data

 * must be read from the Value Cache.

 *

 * Usage notes:

 *

 * Initialization

 *

 *   The value cache must be initialized at the start of the program with zbx_vc_init()

 *   function. To ensure proper removal of shared memory the value cache must be destroyed

 *   upon a program exit with zbx_vc_destroy() function.

 *

 * Adding data

 *

 *   Whenever a new item value is added to system (history tables) the item value must be

 *   also added added to Value Cache with zbx_dc_add_value() function to keep it up to date.

 *

 * Retrieving data

 *

 *   The history data is accessed with zbx_vc_get_values() and zbx_vc_get_value()

 *   functions. Afterwards the retrieved history data must be freed by the caller by using

 *   either zbx_history_record_vector_destroy() function (free the zbx_vc_get_values()

 *   call output) or zbx_history_record_clear() function (free the zbx_vc_get_value() call output).

 *

 * Locking

 *

 *   The cache ensures synchronization between processes by using automatic locks whenever

 *   a cache function (zbx_vc_*) is called and by providing manual cache locking functionality

 *   with zbx_vc_lock()/zbx_vc_unlock() functions.

 *

 */

​

#define ZBX_VC_MODE_NORMAL  0

#define ZBX_VC_MODE_LOWMEM  1

​

/* indicates that all values from database are cached */

#define ZBX_ITEM_STATUS_CACHED_ALL  1

​

/* the cache statistics */

typedef struct