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/>.

**/

​

#include "zbxshmem.h"

​

#include "zbxstr.h"

​

/******************************************************************************

 *                                                                            *

 *                     Some information on memory layout                      *

 *                  ---------------------------------------                   *

 *                                                                            *

 * (*) chunk: a contiguous piece of memory that is either free or used        *

 *                                                                            *

 *                    +-------- size of + --------------+                     *

 *                    |       (8 bytes) |               |                     *

 *                    |                 v               |                     *

 *                    |                                 |                     *

 *                    |    +- allocatable memory --+    |                     *

 *                    |    | (user data goes here) |    |                     *

 *                    v    v                       v    v                     *

 *                                                                            *

 *                |--------|----------------...----|--------|                 *

 *                                                                            *

 *                ^        ^                       ^        ^                 *

 *            8-aligned    |                       |    8-aligned             *

 *                                                                            *

 *                     8-aligned               8-aligned                      *

 *                                                                            *

 *     when a chunk is used, `size' fields have SHMEM_FLG_USED bit set        *

 *                                                                            *

 *     when a chunk is free, the first 2 * ZBX_PTR_SIZE bytes of allocatable  *

 *     memory contain pointers to the previous and next chunks, in that order *

 *                                                                            *

 *     notes:                                                                 *

 *                                                                            *

 *         - user data is nicely 8-aligned                                    *

 *                                                                            *

 *         - size is kept on both left and right ends for quick merging       *

 *           (when freeing a chunk, we can quickly see if the previous        *

 *           and next chunks are free, those will not have SHMEM_FLG_USED)    *

 *                                                                            *

 * (*) free chunks are stored in doubly-linked lists according to their sizes *

 *                                                                            *

 *     a typical situation is thus as follows (1 used chunk, 2 free chunks)   *

 *                                                                            *

 *  +--------------------------- shared memory ----------------------------+  *

 *  |                         (can be misaligned)                          |  *

 *  |                                                                      |  *

 *  |                                                                      |  *

 *  |  +------ chunk A ------+------ chunk B -----+------ chunk C ------+  |  *

 *  |  |       (free)        |       (used)       |       (free)        |  |  *

 *  |  |                     |                    |                     |  |  *

 *  v  v                     v                    v                     v  v  *

 *           prevnext              user data            prevnext              *

 *  #--|----|--------...|----|----|---....---|----|----|--------...|----|--#  *

 *           NULL  |                                     |  NULL              *

 *     ^           |                              ^      |              ^     *

 *     |           |                              |      |              |     *

 *     |           +------------------------------+      |              |     *

 *     |                                                 |              |     *

 *     +-------------------------------------------------+              |     *

 *     |                                                                |     *

 *                                                                            *

 *  lo_bound             `size' fields in chunk B                   hi_bound  *

 *  (aligned)            have SHMEM_FLG_USED bit set               (aligned)  *

 *                                                                            *

 ******************************************************************************/

​

static void *ALIGN4(void *ptr);

static void *ALIGN8(void *ptr);

static void *ALIGNPTR(void *ptr);

​

static zbx_uint64_t mem_proper_alloc_size(zbx_uint64_t size);

static int  mem_bucket_by_size(zbx_uint64_t size);

​

static void mem_set_chunk_size(void *chunk, zbx_uint64_t size);

static void mem_set_used_chunk_size(void *chunk, zbx_uint64_t size);

​

static void *mem_get_prev_chunk(void *chunk);