lbbs/src/section_list.c

/***************************************************************************
                                           section_list.c  -  description
                                                         -------------------
        Copyright            : (C) 2004-2025 by Leaflet
        Email                : leaflet@leafok.com
 ***************************************************************************/

/***************************************************************************
 *                                                                         *
 *   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 3 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 ***************************************************************************/

#define _GNU_SOURCE

#include "section_list.h"
#include "log.h"
#include "trie_dict.h"
#include <stdio.h>
#include <string.h>
#include <signal.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/param.h>
#include <sys/sem.h>
#include <sys/shm.h>
#include <sys/ipc.h>

#ifdef _SEM_SEMUN_UNDEFINED
union semun
{
        int val;                           /* Value for SETVAL */
        struct semid_ds *buf;  /* Buffer for IPC_STAT, IPC_SET */
        unsigned short *array; /* Array for GETALL, SETALL */
        struct seminfo *__buf; /* Buffer for IPC_INFO
                                                          (Linux-specific) */
};
#endif // #ifdef _SEM_SEMUN_UNDEFINED

#define SECTION_TRY_LOCK_WAIT_TIME 1 // second
#define SECTION_TRY_LOCK_TIMES 10

#define ARTICLE_BLOCK_PER_SHM 400                 // sizeof(ARTICLE_BLOCK) * ARTICLE_BLOCK_PER_SHM is the size of each shm segment to allocate
#define ARTICLE_BLOCK_SHM_COUNT_LIMIT 200 // limited by length (8-bit) of proj_id in ftok(path, proj_id)
#define ARTICLE_BLOCK_PER_POOL (ARTICLE_BLOCK_PER_SHM * ARTICLE_BLOCK_SHM_COUNT_LIMIT)

#define CALCULATE_PAGE_THRESHOLD 100 // Adjust to tune performance of move topic

#define SID_STR_LEN 5 // 32-bit + NULL

struct article_block_t
{
        ARTICLE articles[ARTICLE_PER_BLOCK];
        int article_count;
        struct article_block_t *p_next_block;
};
typedef struct article_block_t ARTICLE_BLOCK;

struct article_block_pool_t
{
        int shmid;
        struct
        {
                int shmid;
                void *p_shm;
        } shm_pool[ARTICLE_BLOCK_SHM_COUNT_LIMIT];
        int shm_count;
        ARTICLE_BLOCK *p_block_free_list;
        ARTICLE_BLOCK *p_block[ARTICLE_BLOCK_PER_POOL];
        int block_count;
};
typedef struct article_block_pool_t ARTICLE_BLOCK_POOL;

static ARTICLE_BLOCK_POOL *p_article_block_pool = NULL;

struct section_list_pool_t
{
        int shmid;
        SECTION_LIST sections[BBS_max_section];
        int section_count;
        int semid;
        TRIE_NODE *p_trie_dict_section_by_name;
        TRIE_NODE *p_trie_dict_section_by_sid;
};
typedef struct section_list_pool_t SECTION_LIST_POOL;

static SECTION_LIST_POOL *p_section_list_pool = NULL;

int article_block_init(const char *filename, int block_count)
{
        int shmid;
        int proj_id;
        key_t key;
        size_t size;
        void *p_shm;
        int i;
        int block_count_in_shm;
        ARTICLE_BLOCK *p_block_in_shm;
        ARTICLE_BLOCK **pp_block_next;

        if (p_article_block_pool != NULL)
        {
                log_error("article_block_pool already initialized\n");
                return -1;
        }

        if (block_count > ARTICLE_BLOCK_PER_POOL)
        {
                log_error("article_block_count exceed limit %d\n", ARTICLE_BLOCK_PER_POOL);
                return -2;
        }

        // Allocate shared memory
        proj_id = ARTICLE_BLOCK_SHM_COUNT_LIMIT; // keep different from proj_id used to create block shm
        key = ftok(filename, proj_id);
        if (key == -1)
        {
                log_error("ftok(%s, %d) error (%d)\n", filename, proj_id, errno);
                return -3;
        }

        size = sizeof(ARTICLE_BLOCK_POOL);
        shmid = shmget(key, size, IPC_CREAT | IPC_EXCL | 0600);
        if (shmid == -1)
        {
                log_error("shmget(article_block_pool_shm, size = %d) error (%d)\n", size, errno);
                return -3;
        }
        p_shm = shmat(shmid, NULL, 0);
        if (p_shm == (void *)-1)
        {
                log_error("shmat(shmid = %d) error (%d)\n", shmid, errno);
                return -3;
        }

        p_article_block_pool = p_shm;
        p_article_block_pool->shmid = shmid;

        p_article_block_pool->shm_count = 0;
        pp_block_next = &(p_article_block_pool->p_block_free_list);

        while (block_count > 0)
        {
                block_count_in_shm = MIN(block_count, ARTICLE_BLOCK_PER_SHM);
                block_count -= block_count_in_shm;

                proj_id = p_article_block_pool->shm_count;
                key = ftok(filename, proj_id);
                if (key == -1)
                {
                        log_error("ftok(%s, %d) error (%d)\n", filename, proj_id, errno);
                        article_block_cleanup();
                        return -3;
                }

                size = sizeof(ARTICLE_BLOCK) * (size_t)block_count_in_shm;
                shmid = shmget(key, size, IPC_CREAT | IPC_EXCL | 0600);
                if (shmid == -1)
                {
                        log_error("shmget(shm_index = %d, size = %d) error (%d)\n", p_article_block_pool->shm_count, size, errno);
                        article_block_cleanup();
                        return -3;
                }
                p_shm = shmat(shmid, NULL, 0);
                if (p_shm == (void *)-1)
                {
                        log_error("shmat(shmid = %d) error (%d)\n", shmid, errno);
                        article_block_cleanup();
                        return -3;
                }

                (p_article_block_pool->shm_pool + p_article_block_pool->shm_count)->shmid = shmid;
                (p_article_block_pool->shm_pool + p_article_block_pool->shm_count)->p_shm = p_shm;
                p_article_block_pool->shm_count++;

                p_block_in_shm = p_shm;
                *pp_block_next = p_block_in_shm;

                for (i = 0; i < block_count_in_shm; i++)
                {
                        if (i < block_count_in_shm - 1)
                        {
                                (p_block_in_shm + i)->p_next_block = (p_block_in_shm + i + 1);
                        }
                        else
                        {
                                (p_block_in_shm + i)->p_next_block = NULL;
                                pp_block_next = &((p_block_in_shm + i)->p_next_block);
                        }
                }
        }

        p_article_block_pool->block_count = 0;

        return 0;
}

void article_block_cleanup(void)
{
        int shmid;

        if (p_article_block_pool == NULL)
        {
                return;
        }

        for (int i = 0; i < p_article_block_pool->shm_count; i++)
        {
                if (shmdt((p_article_block_pool->shm_pool + i)->p_shm) == -1)
                {
                        log_error("shmdt(shmid = %d) error (%d)\n", (p_article_block_pool->shm_pool + i)->shmid, errno);
                }

                if (shmctl((p_article_block_pool->shm_pool + i)->shmid, IPC_RMID, NULL) == -1)
                {
                        log_error("shmctl(shmid = %d, IPC_RMID) error (%d)\n", (p_article_block_pool->shm_pool + i)->shmid, errno);
                }
        }

        shmid = p_article_block_pool->shmid;

        if (shmdt(p_article_block_pool) == -1)
        {
                log_error("shmdt(shmid = %d) error (%d)\n", shmid, errno);
        }

        if (shmctl(shmid, IPC_RMID, NULL) == -1)
        {
                log_error("shmctl(shmid = %d, IPC_RMID) error (%d)\n", shmid, errno);
        }

        p_article_block_pool = NULL;
}

inline static ARTICLE_BLOCK *pop_free_article_block(void)
{
        ARTICLE_BLOCK *p_block = NULL;

        if (p_article_block_pool->p_block_free_list != NULL)
        {
                p_block = p_article_block_pool->p_block_free_list;
                p_article_block_pool->p_block_free_list = p_block->p_next_block;
                p_block->p_next_block = NULL;
                p_block->article_count = 0;
        }

        return p_block;
}

inline static void push_free_article_block(ARTICLE_BLOCK *p_block)
{
        p_block->p_next_block = p_article_block_pool->p_block_free_list;
        p_article_block_pool->p_block_free_list = p_block;
}

int article_block_reset(void)
{
        ARTICLE_BLOCK *p_block;

        if (p_article_block_pool == NULL)
        {
                log_error("article_block_pool not initialized\n");
                return -1;
        }

        while (p_article_block_pool->block_count > 0)
        {
                p_article_block_pool->block_count--;
                p_block = p_article_block_pool->p_block[p_article_block_pool->block_count];
                push_free_article_block(p_block);
        }

        return 0;
}

ARTICLE *article_block_find_by_aid(int32_t aid)
{
        ARTICLE_BLOCK *p_block;
        int left;
        int right;
        int mid;

        if (p_article_block_pool == NULL)
        {
                log_error("article_block_pool not initialized\n");
                return NULL;
        }

        if (p_article_block_pool->block_count == 0) // empty
        {
                return NULL;
        }

        left = 0;
        right = p_article_block_pool->block_count;

        // aid in the range [ head aid of blocks[left], tail aid of blocks[right - 1] ]
        while (left < right - 1)
        {
                // get block offset no less than mid value of left and right block offsets
                mid = (left + right) / 2 + (right - left) % 2;

                if (mid >= p_article_block_pool->block_count)
                {
                        log_error("block(mid = %d) is out of boundary\n", mid);
                        return NULL;
                }

                if (aid < p_article_block_pool->p_block[mid]->articles[0].aid)
                {
                        right = mid;
                }
                else
                {
                        left = mid;
                }
        }

        p_block = p_article_block_pool->p_block[left];

        left = 0;
        right = p_block->article_count - 1;

        // aid in the range [ aid of articles[left], aid of articles[right] ]
        while (left < right)
        {
                mid = (left + right) / 2;

                if (aid <= p_block->articles[mid].aid)
                {
                        right = mid;
                }
                else
                {
                        left = mid + 1;
                }
        }

        return (p_block->articles + left);
}

ARTICLE *article_block_find_by_index(int index)
{
        ARTICLE_BLOCK *p_block;

        if (p_article_block_pool == NULL)
        {
                log_error("article_block_pool not initialized\n");
                return NULL;
        }

        if (index < 0 || index / ARTICLE_PER_BLOCK >= p_article_block_pool->block_count)
        {
                log_error("article_block_find_by_index(%d) is out of boundary of block [0, %d)\n", index, p_article_block_pool->block_count);
                return NULL;
        }

        p_block = p_article_block_pool->p_block[index / ARTICLE_PER_BLOCK];

        if (index % ARTICLE_PER_BLOCK >= p_block->article_count)
        {
                log_error("article_block_find_by_index(%d) is out of boundary of article [0, %d)\n", index, p_block->article_count);
                return NULL;
        }

        return (p_block->articles + (index % ARTICLE_PER_BLOCK));
}

extern int section_list_init(const char *filename)
{
        int semid;
        int shmid;
        int proj_id;
        key_t key;
        size_t size;
        void *p_shm;
        union semun arg;
        int i;

        if (p_section_list_pool != NULL)
        {
                section_list_cleanup();
        }

        proj_id = (int)(time(NULL) % getpid());
        key = ftok(filename, proj_id);
        if (key == -1)
        {
                log_error("ftok(%s, %d) error (%d)\n", filename, proj_id, errno);
                return -3;
        }

        // Allocate shared memory
        size = sizeof(SECTION_LIST_POOL);
        shmid = shmget(key, size, IPC_CREAT | IPC_EXCL | 0600);
        if (shmid == -1)
        {
                log_error("shmget(section_list_pool_shm, size = %d) error (%d)\n", size, errno);
                return -3;
        }
        p_shm = shmat(shmid, NULL, 0);
        if (p_shm == (void *)-1)
        {
                log_error("shmat(shmid = %d) error (%d)\n", shmid, errno);
                return -3;
        }

        p_section_list_pool = p_shm;
        p_section_list_pool->shmid = shmid;
        p_section_list_pool->section_count = 0;

        // Allocate semaphore as section locks
        size = 2 * (BBS_max_section + 1); // r_sem and w_sem per section, the last pair for all sections
        semid = semget(key, (int)size, IPC_CREAT | IPC_EXCL | 0600);
        if (semid == -1)
        {
                log_error("semget(section_list_pool_sem, size = %d) error (%d)\n", size, errno);
                return -3;
        }

        // Initialize sem value to 0
        arg.val = 0;
        for (i = 0; i < size; i++)
        {
                if (semctl(semid, i, SETVAL, arg) == -1)
                {
                        log_error("semctl(section_list_pool_sem, SETVAL) error (%d)\n", errno);
                        return -3;
                }
        }

        p_section_list_pool->semid = semid;

        p_section_list_pool->p_trie_dict_section_by_name = trie_dict_create();
        if (p_section_list_pool->p_trie_dict_section_by_name == NULL)
        {
                log_error("trie_dict_create() OOM\n", BBS_max_section);
                return -2;
        }

        p_section_list_pool->p_trie_dict_section_by_sid = trie_dict_create();
        if (p_section_list_pool->p_trie_dict_section_by_sid == NULL)
        {
                log_error("trie_dict_create() OOM\n", BBS_max_section);
                return -2;
        }

        return 0;
}

inline static void sid_to_str(int32_t sid, char *p_sid_str)
{
        uint32_t u_sid;
        int i;

        u_sid = (uint32_t)sid;
        for (i = 0; i < SID_STR_LEN - 1; i++)
        {
                p_sid_str[i] = (char)(u_sid % 255 + 1);
                u_sid /= 255;
        }
        p_sid_str[i] = '\0';
}

SECTION_LIST *section_list_create(int32_t sid, const char *sname, const char *stitle, const char *master_name)
{
        SECTION_LIST *p_section;
        char sid_str[SID_STR_LEN];

        if (p_section_list_pool == NULL)
        {
                log_error("session_list_pool not initialized\n");
                return NULL;
        }

        if (p_section_list_pool->section_count >= BBS_max_section)
        {
                log_error("section_count reach limit %d >= %d\n", p_section_list_pool->section_count, BBS_max_section);
                return NULL;
        }

        sid_to_str(sid, sid_str);

        p_section = p_section_list_pool->sections + p_section_list_pool->section_count;

        p_section->sid = sid;

        strncpy(p_section->sname, sname, sizeof(p_section->sname - 1));
        p_section->sname[sizeof(p_section->sname - 1)] = '\0';

        strncpy(p_section->stitle, stitle, sizeof(p_section->stitle - 1));
        p_section->stitle[sizeof(p_section->stitle - 1)] = '\0';

        strncpy(p_section->master_name, master_name, sizeof(p_section->master_name - 1));
        p_section->master_name[sizeof(p_section->master_name - 1)] = '\0';

        if (trie_dict_set(p_section_list_pool->p_trie_dict_section_by_name, sname, p_section_list_pool->section_count) != 1)
        {
                log_error("trie_dict_set(section, %s, %d) error\n", sname, p_section_list_pool->section_count);
                return NULL;
        }

        if (trie_dict_set(p_section_list_pool->p_trie_dict_section_by_sid, sid_str, p_section_list_pool->section_count) != 1)
        {
                log_error("trie_dict_set(section, %d, %d) error\n", sid, p_section_list_pool->section_count);
                return NULL;
        }

        section_list_reset_articles(p_section);

        p_section_list_pool->section_count++;

        return p_section;
}

void section_list_reset_articles(SECTION_LIST *p_section)
{
        p_section->article_count = 0;
        p_section->topic_count = 0;
        p_section->visible_article_count = 0;
        p_section->visible_topic_count = 0;
        p_section->p_article_head = NULL;
        p_section->p_article_tail = NULL;

        p_section->page_count = 0;
        p_section->last_page_visible_article_count = 0;
}

void section_list_cleanup(void)
{
        int shmid;

        if (p_section_list_pool == NULL)
        {
                return;
        }

        if (p_section_list_pool->p_trie_dict_section_by_name != NULL)
        {
                trie_dict_destroy(p_section_list_pool->p_trie_dict_section_by_name);
                p_section_list_pool->p_trie_dict_section_by_name = NULL;
        }

        if (p_section_list_pool->p_trie_dict_section_by_sid != NULL)
        {
                trie_dict_destroy(p_section_list_pool->p_trie_dict_section_by_sid);
                p_section_list_pool->p_trie_dict_section_by_sid = NULL;
        }

        if (p_section_list_pool != NULL)
        {
                if (semctl(p_section_list_pool->semid, 0, IPC_RMID) == -1)
                {
                        log_error("semctl(semid = %d, IPC_RMID) error (%d)\n", p_section_list_pool->semid, errno);
                }

                shmid = p_section_list_pool->shmid;

                if (shmdt(p_section_list_pool) == -1)
                {
                        log_error("shmdt(shmid = %d) error (%d)\n", shmid, errno);
                }

                if (shmctl(shmid, IPC_RMID, NULL) == -1)
                {
                        log_error("shmctl(shmid = %d, IPC_RMID) error (%d)\n", shmid, errno);
                }

                p_section_list_pool = NULL;
        }
}

SECTION_LIST *section_list_find_by_name(const char *sname)
{
        int64_t index;

        if (p_section_list_pool == NULL)
        {
                log_error("section_list not initialized\n");
                return NULL;
        }

        if (trie_dict_get(p_section_list_pool->p_trie_dict_section_by_name, sname, &index) != 1)
        {
                log_error("trie_dict_get(section, %s) error\n", sname);
                return NULL;
        }

        return (p_section_list_pool->sections + index);
}

SECTION_LIST *section_list_find_by_sid(int32_t sid)
{
        int64_t index;
        char sid_str[SID_STR_LEN];

        if (p_section_list_pool == NULL)
        {
                log_error("section_list not initialized\n");
                return NULL;
        }

        sid_to_str(sid, sid_str);

        if (trie_dict_get(p_section_list_pool->p_trie_dict_section_by_sid, sid_str, &index) != 1)
        {
                log_error("trie_dict_get(section, %d) error\n", sid);
                return NULL;
        }

        return (p_section_list_pool->sections + index);
}

int section_list_append_article(SECTION_LIST *p_section, const ARTICLE *p_article_src)
{
        ARTICLE_BLOCK *p_block;
        int32_t last_aid = 0;
        ARTICLE *p_article;
        ARTICLE *p_topic_head;
        ARTICLE *p_topic_tail;

        if (p_section == NULL || p_article_src == NULL)
        {
                log_error("section_list_append_article() NULL pointer error\n");
                return -1;
        }

        if (p_article_block_pool == NULL)
        {
                log_error("article_block_pool not initialized\n");
                return -1;
        }

        if (p_section->sid != p_article_src->sid)
        {
                log_error("section_list_append_article() error: section sid %d != article sid %d\n", p_section->sid, p_article_src->sid);
                return -2;
        }

        if (p_section->article_count >= BBS_article_limit_per_section)
        {
                log_error("section_list_append_article() error: article_count reach limit in section %d\n", p_section->sid);
                return -2;
        }

        if (p_article_block_pool->block_count == 0 ||
                p_article_block_pool->p_block[p_article_block_pool->block_count - 1]->article_count >= ARTICLE_PER_BLOCK)
        {
                if ((p_block = pop_free_article_block()) == NULL)
                {
                        log_error("pop_free_article_block() error\n");
                        return -2;
                }

                if (p_article_block_pool->block_count > 0)
                {
                        last_aid = p_article_block_pool->p_block[p_article_block_pool->block_count - 1]->articles[ARTICLE_PER_BLOCK - 1].aid;
                }

                p_article_block_pool->p_block[p_article_block_pool->block_count] = p_block;
                p_article_block_pool->block_count++;
        }
        else
        {
                p_block = p_article_block_pool->p_block[p_article_block_pool->block_count - 1];
                last_aid = p_block->articles[p_block->article_count - 1].aid;
        }

        // AID of articles should be strictly ascending
        if (p_article_src->aid <= last_aid)
        {
                log_error("section_list_append_article(aid=%d) error: last_aid=%d\n", p_article_src->aid, last_aid);
                return -3;
        }

        p_article = (p_block->articles + p_block->article_count);
        p_block->article_count++;
        p_section->article_count++;

        // Copy article data
        *p_article = *p_article_src;

        if (p_article->visible)
        {
                p_section->visible_article_count++;
        }

        // Link appended article as tail node of topic bi-directional list
        if (p_article->tid != 0)
        {
                p_topic_head = article_block_find_by_aid(p_article->tid);
                if (p_topic_head == NULL)
                {
                        log_error("search head of topic (aid=%d) error\n", p_article->tid);
                        return -4;
                }

                p_topic_tail = p_topic_head->p_topic_prior;
                if (p_topic_tail == NULL)
                {
                        log_error("tail of topic (aid=%d) is NULL\n", p_article->tid);
                        return -4;
                }
        }
        else
        {
                p_section->topic_count++;

                if (p_article->visible)
                {
                        p_section->visible_topic_count++;
                }

                p_topic_head = p_article;
                p_topic_tail = p_article;
        }

        p_article->p_topic_prior = p_topic_tail;
        p_article->p_topic_next = p_topic_head;
        p_topic_head->p_topic_prior = p_article;
        p_topic_tail->p_topic_next = p_article;

        // Link appended article as tail node of article bi-directional list
        if (p_section->p_article_head == NULL)
        {
                p_section->p_article_head = p_article;
                p_section->p_article_tail = p_article;
        }
        p_article->p_prior = p_section->p_article_tail;
        p_article->p_next = p_section->p_article_head;
        p_section->p_article_head->p_prior = p_article;
        p_section->p_article_tail->p_next = p_article;
        p_section->p_article_tail = p_article;

        // Update page
        if ((p_article->visible && p_section->last_page_visible_article_count % BBS_article_limit_per_page == 0) ||
                p_section->article_count == 1)
        {
                p_section->p_page_first_article[p_section->page_count] = p_article;
                p_section->page_count++;
                p_section->last_page_visible_article_count = 0;
        }

        if (p_article->visible)
        {
                p_section->last_page_visible_article_count++;
        }

        return 0;
}

int section_list_set_article_visible(SECTION_LIST *p_section, int32_t aid, int8_t visible)
{
        ARTICLE *p_article;
        ARTICLE *p_reply;
        int affected_count = 0;

        if (p_section == NULL)
        {
                log_error("section_list_set_article_visible() NULL pointer error\n");
                return -2;
        }

        p_article = article_block_find_by_aid(aid);
        if (p_article == NULL)
        {
                return -1; // Not found
        }

        if (p_section->sid != p_article->sid)
        {
                log_error("section_list_set_article_visible() error: section sid %d != article sid %d\n", p_section->sid, p_article->sid);
                return -2;
        }

        if (p_article->visible == visible)
        {
                return 0; // Already set
        }

        if (visible == 0) // 1 -> 0
        {
                p_section->visible_article_count--;

                if (p_article->tid == 0)
                {
                        p_section->visible_topic_count--;

                        // Set related visible replies to invisible
                        for (p_reply = p_article->p_topic_next; p_reply->tid != 0; p_reply = p_reply->p_topic_next)
                        {
                                if (p_reply->tid != aid)
                                {
                                        log_error("Inconsistent tid = %d found in reply %d of topic %d\n", p_reply->tid, p_reply->aid, aid);
                                        continue;
                                }

                                if (p_reply->visible == 1)
                                {
                                        p_reply->visible = 0;
                                        p_section->visible_article_count--;
                                        affected_count++;
                                }
                        }
                }
        }
        else // 0 -> 1
        {
                p_section->visible_article_count++;

                if (p_article->tid == 0)
                {
                        p_section->visible_topic_count++;
                }
        }

        p_article->visible = visible;
        affected_count++;

        return affected_count;
}

ARTICLE *section_list_find_article_with_offset(SECTION_LIST *p_section, int32_t aid, int32_t *p_page, int32_t *p_offset, ARTICLE **pp_next)
{
        ARTICLE *p_article;
        int left;
        int right;
        int mid;

        *p_page = -1;
        *p_offset = -1;
        *pp_next = NULL;

        if (p_section == NULL)
        {
                log_error("section_list_find_article_with_offset() NULL pointer error\n");
                return NULL;
        }

        if (p_section->article_count == 0) // empty
        {
                *p_page = 0;
                *p_offset = 0;
                return NULL;
        }

        left = 0;
        right = p_section->page_count;

        // aid in the range [ head aid of pages[left], tail aid of pages[right - 1] ]
        while (left < right - 1)
        {
                // get page id no less than mid value of left page id and right page id
                mid = (left + right) / 2 + (right - left) % 2;

                if (mid >= p_section->page_count)
                {
                        log_error("page id (mid = %d) is out of boundary\n", mid);
                        return NULL;
                }

                if (aid < p_section->p_page_first_article[mid]->aid)
                {
                        right = mid;
                }
                else
                {
                        left = mid;
                }
        }

        *p_page = left;

        p_article = p_section->p_page_first_article[*p_page];

        // p_section->p_page_first_article[*p_page]->aid <= aid < p_section->p_page_first_article[*p_page + 1]->aid
        right = (*p_page == MAX(0, p_section->page_count - 1) ? INT32_MAX : p_section->p_page_first_article[*p_page + 1]->aid);

        // left will be the offset of article found or offset to insert
        left = 0;

        while (aid > p_article->aid)
        {
                p_article = p_article->p_next;
                left++;

                if (aid == p_article->aid)
                {
                        *pp_next = p_article->p_next;
                        break;
                }

                // over last article in the page
                if (p_article == p_section->p_article_head || p_article->aid >= right)
                {
                        *pp_next = (p_article == p_section->p_article_head ? p_section->p_article_head : p_section->p_page_first_article[*p_page + 1]);
                        *p_offset = left;
                        return NULL; // not found
                }
        }

        if (aid < p_article->aid)
        {
                *pp_next = p_article;
                p_article = NULL; // not found
        }
        else // aid == p_article->aid
        {
                *pp_next = p_article->p_next;
        }

        *p_offset = left;

        return p_article;
}

int section_list_calculate_page(SECTION_LIST *p_section, int32_t start_aid)
{
        ARTICLE *p_article;
        ARTICLE *p_next;
        int32_t page;
        int32_t offset;
        int visible_article_count;
        int page_head_set;

        if (p_section == NULL)
        {
                log_error("section_list_calculate_page() NULL pointer error\n");
                return -1;
        }

        if (p_section->article_count == 0) // empty
        {
                p_section->page_count = 0;
                p_section->last_page_visible_article_count = 0;

                return 0;
        }

        if (start_aid > 0)
        {
                p_article = article_block_find_by_aid(start_aid);
                if (p_article == NULL)
                {
                        return -1; // Not found
                }

                if (p_section->sid != p_article->sid)
                {
                        log_error("section_list_calculate_page() error: section sid %d != start article sid %d\n", p_section->sid, p_article->sid);
                        return -2;
                }

                p_article = section_list_find_article_with_offset(p_section, start_aid, &page, &offset, &p_next);
                if (p_article == NULL)
                {
                        if (page < 0)
                        {
                                return -1;
                        }
                        log_error("section_list_calculate_page() aid = %d not found in section sid = %d\n",
                                          start_aid, p_section->sid);
                        return -2;
                }

                if (offset > 0)
                {
                        p_article = p_section->p_page_first_article[page];
                }
        }
        else
        {
                p_article = p_section->p_article_head;
                page = 0;
                offset = 0;
        }

        visible_article_count = 0;
        page_head_set = 0;

        do
        {
                if (!page_head_set && visible_article_count == 0)
                {
                        p_section->p_page_first_article[page] = p_article;
                        page_head_set = 1;
                }

                if (p_article->visible)
                {
                        visible_article_count++;
                }

                p_article = p_article->p_next;

                // skip remaining invisible articles
                while (p_article->visible == 0 && p_article != p_section->p_article_head)
                {
                        p_article = p_article->p_next;
                }

                if (visible_article_count >= BBS_article_limit_per_page && p_article != p_section->p_article_head)
                {
                        page++;
                        visible_article_count = 0;
                        page_head_set = 0;

                        if (page >= BBS_article_limit_per_section / BBS_article_limit_per_page && p_article != p_section->p_article_head)
                        {
                                log_error("Count of page exceed limit in section %d\n", p_section->sid);
                                break;
                        }
                }
        } while (p_article != p_section->p_article_head);

        p_section->page_count = page + (visible_article_count > 0 ? 1 : 0);
        p_section->last_page_visible_article_count = visible_article_count;

        return 0;
}

int article_count_of_topic(int32_t aid)
{
        ARTICLE *p_article;
        int article_count;

        p_article = article_block_find_by_aid(aid);
        if (p_article == NULL)
        {
                return 0; // Not found
        }

        article_count = 0;

        do
        {
                if (p_article->tid != 0 && p_article->tid != aid)
                {
                        log_error("article_count_of_topic(%d) error: article %d not linked to the topic\n", aid, p_article->aid);
                        break;
                }

                article_count++;
                p_article = p_article->p_topic_next;
        } while (p_article->aid != aid);

        return article_count;
}

int section_list_move_topic(SECTION_LIST *p_section_src, SECTION_LIST *p_section_dest, int32_t aid)
{
        ARTICLE *p_article;
        ARTICLE *p_next;
        int32_t page;
        int32_t offset;
        int32_t move_article_count;
        int32_t dest_article_count_old;
        int32_t last_unaffected_aid_src;
        int32_t first_inserted_aid_dest;
        int move_counter;

        if (p_section_dest == NULL)
        {
                log_error("section_list_move_topic() NULL pointer error\n");
                return -1;
        }

        if ((p_article = article_block_find_by_aid(aid)) == NULL)
        {
                log_error("section_list_move_topic() error: article %d not found in block\n", aid);
                return -2;
        }

        if (p_section_src->sid != p_article->sid)
        {
                log_error("section_list_move_topic() error: src section sid %d != article %d sid %d\n",
                                  p_section_src->sid, p_article->aid, p_article->sid);
                return -2;
        }

        if (p_article->tid != 0)
        {
                log_error("section_list_move_topic(aid = %d) error: article is not head of topic, tid = %d\n", aid, p_article->tid);
                return -2;
        }

        last_unaffected_aid_src = (p_article == p_section_src->p_article_head ? 0 : p_article->p_prior->aid);

        move_article_count = article_count_of_topic(aid);
        if (move_article_count <= 0)
        {
                log_error("article_count_of_topic(aid = %d) <= 0\n", aid);
                return -2;
        }

        if (p_section_dest->article_count + move_article_count > BBS_article_limit_per_section)
        {
                log_error("section_list_move_topic() error: article_count %d reach limit in section %d\n",
                                  p_section_dest->article_count + move_article_count, p_section_dest->sid);
                return -3;
        }

        dest_article_count_old = p_section_dest->article_count;
        move_counter = 0;
        first_inserted_aid_dest = p_article->aid;

        do
        {
                if (p_section_src->sid != p_article->sid)
                {
                        log_error("section_list_move_topic() error: src section sid %d != article %d sid %d\n",
                                          p_section_src->sid, p_article->aid, p_article->sid);
                        return -2;
                }

                // Remove from bi-directional article list of src section
                if (p_section_src->p_article_head == p_article)
                {
                        p_section_src->p_article_head = p_article->p_next;
                }
                if (p_section_src->p_article_tail == p_article)
                {
                        p_section_src->p_article_tail = p_article->p_prior;
                }
                if (p_section_src->p_article_head == p_article) // || p_section_src->p_article_tail == p_article
                {
                        p_section_src->p_article_head = NULL;
                        p_section_src->p_article_tail = NULL;
                }

                p_article->p_prior->p_next = p_article->p_next;
                p_article->p_next->p_prior = p_article->p_prior;

                // Update sid of article
                p_article->sid = p_section_dest->sid;

                if (section_list_find_article_with_offset(p_section_dest, p_article->aid, &page, &offset, &p_next) != NULL)
                {
                        log_error("section_list_move_topic() error: article %d already in section %d\n", p_article->aid, p_section_dest->sid);
                        return -4;
                }

                // Insert into bi-directional article list of dest section
                if (p_next == NULL) // empty section
                {
                        p_section_dest->p_article_head = p_article;
                        p_section_dest->p_article_tail = p_article;
                        p_article->p_prior = p_article;
                        p_article->p_next = p_article;
                }
                else
                {
                        if (p_section_dest->p_article_head == p_next)
                        {
                                if (p_article->aid < p_next->aid)
                                {
                                        p_section_dest->p_article_head = p_article;
                                }
                                else // p_article->aid > p_next->aid
                                {
                                        p_section_dest->p_article_tail = p_article;
                                }
                        }

                        p_article->p_prior = p_next->p_prior;
                        p_article->p_next = p_next;
                        p_next->p_prior->p_next = p_article;
                        p_next->p_prior = p_article;
                }

                // Update article / topic counter of src / desc section
                p_section_src->article_count--;
                p_section_dest->article_count++;
                if (p_article->tid == 0)
                {
                        p_section_src->topic_count--;
                        p_section_dest->topic_count++;
                }

                // Update visible article / topic counter of src / desc section
                if (p_article->visible)
                {
                        p_section_src->visible_article_count--;
                        p_section_dest->visible_article_count++;
                        if (p_article->tid == 0)
                        {
                                p_section_src->visible_topic_count--;
                                p_section_dest->visible_topic_count++;
                        }
                }

                // Update page for empty dest section
                if (p_section_dest->article_count == 1)
                {
                        p_section_dest->p_page_first_article[0] = p_article;
                        p_section_dest->page_count = 1;
                        p_section_dest->last_page_visible_article_count = (p_article->visible ? 1 : 0);
                }

                p_article = p_article->p_topic_next;

                move_counter++;
                if (move_counter % CALCULATE_PAGE_THRESHOLD == 0)
                {
                        // Re-calculate pages of desc section
                        if (section_list_calculate_page(p_section_dest, first_inserted_aid_dest) < 0)
                        {
                                log_error("section_list_calculate_page(dest section = %d, aid = %d) error\n",
                                                  p_section_dest->sid, first_inserted_aid_dest);
                        }

                        first_inserted_aid_dest = p_article->aid;
                }
        } while (p_article->aid != aid);

        if (p_section_dest->article_count - dest_article_count_old != move_article_count)
        {
                log_error("section_list_move_topic() error: count of moved articles %d != %d\n",
                                  p_section_dest->article_count - dest_article_count_old, move_article_count);
        }

        // Re-calculate pages of src section
        if (section_list_calculate_page(p_section_src, last_unaffected_aid_src) < 0)
        {
                log_error("section_list_calculate_page(src section = %d, aid = %d) error at aid = %d\n",
                                  p_section_src->sid, last_unaffected_aid_src, aid);
        }

        if (move_counter % CALCULATE_PAGE_THRESHOLD != 0)
        {
                // Re-calculate pages of desc section
                if (section_list_calculate_page(p_section_dest, first_inserted_aid_dest) < 0)
                {
                        log_error("section_list_calculate_page(dest section = %d, aid = %d) error\n",
                                          p_section_dest->sid, first_inserted_aid_dest);
                }
        }

        return move_article_count;
}

int get_section_index(SECTION_LIST *p_section)
{
        int index;

        if (p_section_list_pool == NULL)
        {
                log_error("get_section_index() error: uninitialized\n");
                return -1;
        }

        if (p_section == NULL)
        {
                index = BBS_max_section;
        }
        else
        {
                index = (int)(p_section - p_section_list_pool->sections);
                if (index < 0 || index >= BBS_max_section)
                {
                        log_error("get_section_index(%d) error: index out of range\n", index);
                        return -2;
                }
        }

        return index;
}

int section_list_try_rd_lock(SECTION_LIST *p_section, int wait_sec)
{
        int index;
        struct sembuf sops[4];
        struct timespec timeout;
        int ret;

        index = get_section_index(p_section);
        if (index < 0)
        {
                return -2;
        }

        sops[0].sem_num = (unsigned short)(index * 2 + 1); // w_sem of section index
        sops[0].sem_op = 0;                                                                // wait until unlocked
        sops[0].sem_flg = 0;

        sops[1].sem_num = (unsigned short)(index * 2); // r_sem of section index
        sops[1].sem_op = 1;                                                        // lock
        sops[1].sem_flg = SEM_UNDO;                                        // undo on terminate

        // Read lock on any specific section will also acquire single read lock on "all section"
        // so that write lock on all section only need to acquire single write on on "all section"
        // rather than to acquire multiple write locks on all the available sections.
        if (index != BBS_max_section)
        {
                sops[2].sem_num = BBS_max_section * 2 + 1; // w_sem of all section
                sops[2].sem_op = 0;                                                // wait until unlocked
                sops[2].sem_flg = 0;

                sops[3].sem_num = BBS_max_section * 2; // r_sem of all section
                sops[3].sem_op = 1;                                        // lock
                sops[3].sem_flg = SEM_UNDO;                        // undo on terminate
        }

        timeout.tv_sec = wait_sec;
        timeout.tv_nsec = 0;

        ret = semtimedop(p_section_list_pool->semid, sops, (index == BBS_max_section ? 2 : 4), &timeout);
        if (ret == -1 && errno != EAGAIN && errno != EINTR)
        {
                log_error("semtimedop(index = %d, lock read) error %d\n", index, errno);
        }

        return ret;
}

int section_list_try_rw_lock(SECTION_LIST *p_section, int wait_sec)
{
        int index;
        struct sembuf sops[3];
        struct timespec timeout;
        int ret;

        index = get_section_index(p_section);
        if (index < 0)
        {
                return -2;
        }

        sops[0].sem_num = (unsigned short)(index * 2 + 1); // w_sem of section index
        sops[0].sem_op = 0;                                                                // wait until unlocked
        sops[0].sem_flg = 0;

        sops[1].sem_num = (unsigned short)(index * 2 + 1); // w_sem of section index
        sops[1].sem_op = 1;                                                                // lock
        sops[1].sem_flg = SEM_UNDO;                                                // undo on terminate

        sops[2].sem_num = (unsigned short)(index * 2); // r_sem of section index
        sops[2].sem_op = 0;                                                        // wait until unlocked
        sops[2].sem_flg = 0;

        timeout.tv_sec = wait_sec;
        timeout.tv_nsec = 0;

        ret = semtimedop(p_section_list_pool->semid, sops, 3, &timeout);
        if (ret == -1 && errno != EAGAIN && errno != EINTR)
        {
                log_error("semtimedop(index = %d, lock write) error %d\n", index, errno);
        }

        return ret;
}

int section_list_rd_unlock(SECTION_LIST *p_section)
{
        int index;
        struct sembuf sops[2];
        int ret;

        index = get_section_index(p_section);
        if (index < 0)
        {
                return -2;
        }

        sops[0].sem_num = (unsigned short)(index * 2); // r_sem of section index
        sops[0].sem_op = -1;                                               // unlock
        sops[0].sem_flg = IPC_NOWAIT | SEM_UNDO;           // no wait

        if (index != BBS_max_section)
        {
                sops[1].sem_num = BBS_max_section * 2;   // r_sem of all section
                sops[1].sem_op = -1;                                     // unlock
                sops[1].sem_flg = IPC_NOWAIT | SEM_UNDO; // no wait
        }

        ret = semop(p_section_list_pool->semid, sops, (index == BBS_max_section ? 1 : 2));
        if (ret == -1 && errno != EAGAIN && errno != EINTR)
        {
                log_error("semop(index = %d, unlock read) error %d\n", index, errno);
        }

        return ret;
}

int section_list_rw_unlock(SECTION_LIST *p_section)
{
        int index;
        struct sembuf sops[1];
        int ret;

        index = get_section_index(p_section);
        if (index < 0)
        {
                return -2;
        }

        sops[0].sem_num = (unsigned short)(index * 2 + 1); // w_sem of section index
        sops[0].sem_op = -1;                                                       // unlock
        sops[0].sem_flg = IPC_NOWAIT | SEM_UNDO;                   // no wait

        ret = semop(p_section_list_pool->semid, sops, 1);
        if (ret == -1 && errno != EAGAIN && errno != EINTR)
        {
                log_error("semop(index = %d, unlock write) error %d\n", index, errno);
        }

        return ret;
}

int section_list_rd_lock(SECTION_LIST *p_section)
{
        int timer = 0;
        int sid = (p_section == NULL ? 0 : p_section->sid);
        int ret = -1;

        while (!SYS_server_exit)
        {
                ret = section_list_try_rd_lock(p_section, SECTION_TRY_LOCK_WAIT_TIME);
                if (ret == 0) // success
                {
                        break;
                }
                else if (errno == EAGAIN || errno == EINTR) // retry
                {
                        timer++;
                        if (timer % SECTION_TRY_LOCK_TIMES == 0)
                        {
                                log_error("section_list_rd_lock() tried %d times on section %d\n", sid, timer);
                        }
                }
                else // failed
                {
                        log_error("section_list_rd_lock() failed on section %d\n", sid);
                        break;
                }
        }

        return ret;
}

int section_list_rw_lock(SECTION_LIST *p_section)
{
        int timer = 0;
        int sid = (p_section == NULL ? 0 : p_section->sid);
        int ret = -1;

        while (!SYS_server_exit)
        {
                ret = section_list_try_rw_lock(p_section, SECTION_TRY_LOCK_WAIT_TIME);
                if (ret == 0) // success
                {
                        break;
                }
                else if (errno == EAGAIN || errno == EINTR) // retry
                {
                        timer++;
                        if (timer % SECTION_TRY_LOCK_TIMES == 0)
                        {
                                log_error("acquire_section_rw_lock() tried %d times on section %d\n", sid, timer);
                        }
                }
                else // failed
                {
                        log_error("acquire_section_rw_lock() failed on section %d\n", sid);
                        break;
                }
        }

        return ret;
}
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