頭文件head.h

#ifndef __THREADPOOL_H_
#define __THREADPOOL_H_

typedef struct threadpool_t threadpool_t;

/**
 * @function threadpool_create
 * @descCreates a threadpool_t object.
 * @param thr_num  thread num
 * @param max_thr_num  max thread size
 * @param queue_max_size   size of the queue.
 * @return a newly created thread pool or NULL
 */
threadpool_t *threadpool_create(int min_thr_num, int max_thr_num, int queue_max_size);

/**
 * @function threadpool_add
 * @desc add a new task in the queue of a thread pool
 * @param pool     Thread pool to which add the task.
 * @param function Pointer to the function that will perform the task.
 * @param argument Argument to be passed to the function.
 * @return 0 if all goes well,else -1
 */
int threadpool_add(threadpool_t *pool, void*(*function)(void *arg), void *arg);

/**
 * @function threadpool_destroy
 * @desc Stops and destroys a thread pool.
 * @param pool  Thread pool to destroy.
 * @return 0 if destory success else -1
 */
int threadpool_destroy(threadpool_t *pool);

/**
 * @desc get the thread num
 * @pool pool threadpool
 * @return # of the thread
 */
int threadpool_all_threadnum(threadpool_t *pool);

/**
 * desc get the busy thread num
 * @param pool threadpool
 * return # of the busy thread
 */
int threadpool_busy_threadnum(threadpool_t *pool);

#endif

main.c

#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>
#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <signal.h>
#include <errno.h>
#include "threadpool.h"

#define DEFAULT_TIME 10                 /*10s檢測一次*/
#define MIN_WAIT_TASK_NUM 10            /*如果queue_size > MIN_WAIT_TASK_NUM 添加新的線程到線程池*/ 
#define DEFAULT_THREAD_VARY 10          /*每次創建和銷毀線程的個數*/
#define true 1
#define false 0

typedef struct {
    void *(*function)(void *);          /* 函數指針，回調函數 */
    void *arg;                          /* 上面函數的參數 */
} threadpool_task_t;                    /* 各子線程任務結構體 */

/* 描述線程池相關信息 */
struct threadpool_t {
    pthread_mutex_t lock;               /* 用於鎖住本結構體 */    
    pthread_mutex_t thread_counter;     /* 記錄忙狀態線程個數de瑣 -- busy_thr_num */
    pthread_cond_t queue_not_full;      /* 當任務隊列滿時，添加任務的線程阻塞，等待此條件變量 */
    pthread_cond_t queue_not_empty;     /* 任務隊列裏不為空時，通知等待任務的線程 */

    pthread_t *threads;                 /* 存放線程池中每個線程的tid。數組 */
    pthread_t adjust_tid;               /* 存管理線程tid */
    threadpool_task_t *task_queue;      /* 任務隊列 */

    int min_thr_num;                    /* 線程池最小線程數 */
    int max_thr_num;                    /* 線程池最大線程數 */
    int live_thr_num;                   /* 當前存活線程個數 */
    int busy_thr_num;                   /* 忙狀態線程個數 */
    int wait_exit_thr_num;              /* 要銷毀的線程個數 */

    int queue_front;                    /* task_queue隊頭下標 */
    int queue_rear;                     /* task_queue隊尾下標 */
    int queue_size;                     /* task_queue隊中實際任務數 */
    int queue_max_size;                 /* task_queue隊列可容納任務數上限 */

    int shutdown;                       /* 標誌位，線程池使用狀態，true或false */
};

/**
 * @function void *threadpool_thread(void *threadpool)
 * @desc the worker thread
 * @param threadpool the pool which own the thread
 */
void *threadpool_thread(void *threadpool);

/**
 * @function void *adjust_thread(void *threadpool);
 * @desc manager thread
 * @param threadpool the threadpool
 */
void *adjust_thread(void *threadpool);

/**
 * check a thread is alive
 */
int is_thread_alive(pthread_t tid);
int threadpool_free(threadpool_t *pool);

threadpool_t *threadpool_create(int min_thr_num, int max_thr_num, int queue_max_size)
{
    int i;
    threadpool_t *pool = NULL;
    do {
        if((pool = (threadpool_t *)malloc(sizeof(threadpool_t))) == NULL) {  
            printf("malloc threadpool fail");
            break;/*跳出do while*/
        }

        pool->min_thr_num = min_thr_num;
        pool->max_thr_num = max_thr_num;
        pool->busy_thr_num = 0;
        pool->live_thr_num = min_thr_num;               /* 活著的線程數 初值=最小線程數 */
        pool->queue_size = 0;                           /* 有0個產品 */
        pool->queue_max_size = queue_max_size;
        pool->queue_front = 0;
        pool->queue_rear = 0;
        pool->shutdown = false;                         /* 不關閉線程池 */

        /* 根據最大線程上限數， 給工作線程數組開辟空間, 並清零 */
        pool->threads = (pthread_t *)malloc(sizeof(pthread_t)*max_thr_num); 
        if (pool->threads == NULL) {
            printf("malloc threads fail");
            break;
        }
        memset(pool->threads, 0, sizeof(pthread_t)*max_thr_num);

        /* 隊列開辟空間 */
        pool->task_queue = (threadpool_task_t *)malloc(sizeof(threadpool_task_t)*queue_max_size);
        if (pool->task_queue == NULL) {
            printf("malloc task_queue fail");
            break;
        }

        /* 初始化互斥瑣、條件變量 */
        if (pthread_mutex_init(&(pool->lock), NULL) != 0
                || pthread_mutex_init(&(pool->thread_counter), NULL) != 0
                || pthread_cond_init(&(pool->queue_not_empty), NULL) != 0
                || pthread_cond_init(&(pool->queue_not_full), NULL) != 0)
        {
            printf("init the lock or cond fail");
            break;
        }

        /* 啟動 min_thr_num 個 work thread */
        for (i = 0; i < min_thr_num; i++) {
            pthread_create(&(pool->threads[i]), NULL, threadpool_thread, (void *)pool);/*pool指向當前線程池*/
            printf("start thread 0x%x...\n", (unsigned int)pool->threads[i]);
        }
        pthread_create(&(pool->adjust_tid), NULL, adjust_thread, (void *)pool);/* 啟動管理者線程 */

        return pool;

    } while (0);

    threadpool_free(pool);      /* 前面代碼調用失敗時，釋放poll存儲空間 */

    return NULL;
}

/* 向線程池中 添加一個任務 */
int threadpool_add(threadpool_t *pool, void*(*function)(void *arg), void *arg)
{
    pthread_mutex_lock(&(pool->lock));

    /* ==為真，隊列已經滿， 調wait阻塞 */
    while ((pool->queue_size == pool->queue_max_size) && (!pool->shutdown)) {
        pthread_cond_wait(&(pool->queue_not_full), &(pool->lock));
    }
    if (pool->shutdown) {
        pthread_mutex_unlock(&(pool->lock));
    }

    /* 清空 工作線程 調用的回調函數 的參數arg */
    if (pool->task_queue[pool->queue_rear].arg != NULL) {
        free(pool->task_queue[pool->queue_rear].arg);
        pool->task_queue[pool->queue_rear].arg = NULL;
    }
    /*添加任務到任務隊列裏*/
    pool->task_queue[pool->queue_rear].function = function;
    pool->task_queue[pool->queue_rear].arg = arg;
    pool->queue_rear = (pool->queue_rear + 1) % pool->queue_max_size;       /* 隊尾指針移動, 模擬環形 */
    pool->queue_size++;

    /*添加完任務後，隊列不為空，喚醒線程池中 等待處理任務的線程*/
    pthread_cond_signal(&(pool->queue_not_empty));
    pthread_mutex_unlock(&(pool->lock));

    return 0;
}

/* 線程池中各個工作線程 */
void *threadpool_thread(void *threadpool)
{
    threadpool_t *pool = (threadpool_t *)threadpool;
    threadpool_task_t task;

    while (true) {
        /* Lock must be taken to wait on conditional variable */
        /*剛創建出線程，等待任務隊列裏有任務，否則阻塞等待任務隊列裏有任務後再喚醒接收任務*/
        pthread_mutex_lock(&(pool->lock));

        /*queue_size == 0 說明沒有任務，調 wait 阻塞在條件變量上, 若有任務，跳過該while*/
        while ((pool->queue_size == 0) && (!pool->shutdown)) {  
            printf("thread 0x%x is waiting\n", (unsigned int)pthread_self());
            pthread_cond_wait(&(pool->queue_not_empty), &(pool->lock));

            /*清除指定數目的空閑線程，如果要結束的線程個數大於0，結束線程*/
            if (pool->wait_exit_thr_num > 0) {
                pool->wait_exit_thr_num--;

                /*如果線程池裏線程個數大於最小值時可以結束當前線程*/
                if (pool->live_thr_num > pool->min_thr_num) {
                    printf("thread 0x%x is exiting\n", (unsigned int)pthread_self());
                    pool->live_thr_num--;
                    pthread_mutex_unlock(&(pool->lock));
                    pthread_exit(NULL);
                }
            }
        }

        /*如果指定了true，要關閉線程池裏的每個線程，自行退出處理*/
        if (pool->shutdown) {
            pthread_mutex_unlock(&(pool->lock));
            printf("thread 0x%x is exiting\n", (unsigned int)pthread_self());
            pthread_exit(NULL);     /* 線程自行結束 */
        }

        /*從任務隊列裏獲取任務, 是一個出隊操作*/
        task.function = pool->task_queue[pool->queue_front].function;
        task.arg = pool->task_queue[pool->queue_front].arg;

        pool->queue_front = (pool->queue_front + 1) % pool->queue_max_size;       /* 出隊，模擬環形隊列 */
        pool->queue_size--;

        /*通知可以有新的任務添加進來*/
        pthread_cond_broadcast(&(pool->queue_not_full));

        /*任務取出後，立即將 線程池瑣 釋放*/
        pthread_mutex_unlock(&(pool->lock));

        /*執行任務*/ 
        printf("thread 0x%x start working\n", (unsigned int)pthread_self());
        pthread_mutex_lock(&(pool->thread_counter));                            /*忙狀態線程數變量瑣*/
        pool->busy_thr_num++;                                                   /*忙狀態線程數+1*/
        pthread_mutex_unlock(&(pool->thread_counter));
        (*(task.function))(task.arg);                                           /*執行回調函數任務*/
        //task.function(task.arg);                                              /*執行回調函數任務*/

        /*任務結束處理*/ 
        printf("thread 0x%x end working\n", (unsigned int)pthread_self());
        pthread_mutex_lock(&(pool->thread_counter));
        pool->busy_thr_num--;                                       /*處理掉一個任務，忙狀態數線程數-1*/
        pthread_mutex_unlock(&(pool->thread_counter));
    }

    pthread_exit(NULL);
}

/* 管理線程 */
void *adjust_thread(void *threadpool)
{
    int i;
    threadpool_t *pool = (threadpool_t *)threadpool;
    while (!pool->shutdown) {

        sleep(DEFAULT_TIME);                                    /*定時 對線程池管理*/

        pthread_mutex_lock(&(pool->lock));
        int queue_size = pool->queue_size;                      /* 關註 任務數 */
        int live_thr_num = pool->live_thr_num;                  /* 存活 線程數 */
        pthread_mutex_unlock(&(pool->lock));

        pthread_mutex_lock(&(pool->thread_counter));
        int busy_thr_num = pool->busy_thr_num;                  /* 忙著的線程數 */
        pthread_mutex_unlock(&(pool->thread_counter));

        /* 創建新線程 算法： 任務數大於最小線程池個數, 且存活的線程數少於最大線程個數時 如：30>=10 && 40<100*/
        if (queue_size >= MIN_WAIT_TASK_NUM && live_thr_num < pool->max_thr_num) {
            pthread_mutex_lock(&(pool->lock));  
            int add = 0;

            /*一次增加 DEFAULT_THREAD 個線程*/
            for (i = 0; i < pool->max_thr_num && add < DEFAULT_THREAD_VARY
                    && pool->live_thr_num < pool->max_thr_num; i++) {
                if (pool->threads[i] == 0 || !is_thread_alive(pool->threads[i])) {
                    pthread_create(&(pool->threads[i]), NULL, threadpool_thread, (void *)pool);
                    add++;
                    pool->live_thr_num++;
                }
            }

            pthread_mutex_unlock(&(pool->lock));
        }

        /* 銷毀多余的空閑線程 算法：忙線程X2 小於 存活的線程數 且 存活的線程數 大於 最小線程數時*/
        if ((busy_thr_num * 2) < live_thr_num  &&  live_thr_num > pool->min_thr_num) {

            /* 一次銷毀DEFAULT_THREAD個線程, 隨機10個即可 */
            pthread_mutex_lock(&(pool->lock));
            pool->wait_exit_thr_num = DEFAULT_THREAD_VARY;      /* 要銷毀的線程數 設置為10 */
            pthread_mutex_unlock(&(pool->lock));

            for (i = 0; i < DEFAULT_THREAD_VARY; i++) {
                /* 通知處在空閑狀態的線程, 他們會自行終止*/
                pthread_cond_signal(&(pool->queue_not_empty));
            }
        }
    }

    return NULL;
}

int threadpool_destroy(threadpool_t *pool)
{
    int i;
    if (pool == NULL) {
        return -1;
    }
    pool->shutdown = true;

    /*先銷毀管理線程*/
    pthread_join(pool->adjust_tid, NULL);

    for (i = 0; i < pool->live_thr_num; i++) {
        /*通知所有的空閑線程*/
        pthread_cond_broadcast(&(pool->queue_not_empty));
    }
    for (i = 0; i < pool->live_thr_num; i++) {
        pthread_join(pool->threads[i], NULL);
    }
    threadpool_free(pool);

    return 0;
}

int threadpool_free(threadpool_t *pool)
{
    if (pool == NULL) {
        return -1;
    }

    if (pool->task_queue) {
        free(pool->task_queue);
    }
    if (pool->threads) {
        free(pool->threads);
        pthread_mutex_lock(&(pool->lock));
        pthread_mutex_destroy(&(pool->lock));
        pthread_mutex_lock(&(pool->thread_counter));
        pthread_mutex_destroy(&(pool->thread_counter));
        pthread_cond_destroy(&(pool->queue_not_empty));
        pthread_cond_destroy(&(pool->queue_not_full));
    }
    free(pool);
    pool = NULL;

    return 0;
}

int threadpool_all_threadnum(threadpool_t *pool)
{
    int all_threadnum = -1;
    pthread_mutex_lock(&(pool->lock));
    all_threadnum = pool->live_thr_num;
    pthread_mutex_unlock(&(pool->lock));
    return all_threadnum;
}

int threadpool_busy_threadnum(threadpool_t *pool)
{
    int busy_threadnum = -1;
    pthread_mutex_lock(&(pool->thread_counter));
    busy_threadnum = pool->busy_thr_num;
    pthread_mutex_unlock(&(pool->thread_counter));
    return busy_threadnum;
}

int is_thread_alive(pthread_t tid)
{
    int kill_rc = pthread_kill(tid, 0);     //發0號信號，測試線程是否存活
    if (kill_rc == ESRCH) {
        return false;
    }

    return true;
}

/*測試*/ 

#if 1
/* 線程池中的線程，模擬處理業務 */
void *process(void *arg)
{
    printf("thread 0x%x working on task %d\n ",(unsigned int)pthread_self(),*(int *)arg);
    sleep(1);
    printf("task %d is end\n",*(int *)arg);

    return NULL;
}
int main(void)
{
    /*threadpool_t *threadpool_create(int min_thr_num, int max_thr_num, int queue_max_size);*/

    threadpool_t *thp = threadpool_create(3,100,100);/*創建線程池，池裏最小3個線程，最大100，隊列最大100*/
    printf("pool inited");

    //int *num = (int *)malloc(sizeof(int)*20);
    int num[20], i;
    for (i = 0; i < 20; i++) {
        num[i]=i;
        printf("add task %d\n",i);
        threadpool_add(thp, process, (void*)&num[i]);     /* 向線程池中添加任務 */
    }
    sleep(10);                                          /* 等子線程完成任務 */
    threadpool_destroy(thp);

    return 0;
}

線程池代碼