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int zbx_vc_get_values(zbx_uint64_t itemid, unsigned char value_type, zbx_vector_history_record_t *values,/*** Zabbix** Copyright (C) 2001-2023 Zabbix SIA**** 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; either version 2 of the License, or** (at your option) any later version.**** 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 02110-1301, USA.**//* * 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. * */