linux pthreadpool实现和线程池的用处

#include "threadpool.h"

void* work(void* arg)
{
    char *p = (char*) arg;
    printf("threadpool callback fuction : %s.\n", p);
    sleep(1);
}

int main(void)
{
    struct threadpool *pool = threadpool_init(10, 20);
    threadpool_add_job(pool, work, "1");
    threadpool_add_job(pool, work, "2");
    threadpool_add_job(pool, work, "3");
    threadpool_add_job(pool, work, "4");
    threadpool_add_job(pool, work, "5");
    threadpool_add_job(pool, work, "6");
    threadpool_add_job(pool, work, "7");
    threadpool_add_job(pool, work, "8");
    threadpool_add_job(pool, work, "9");
    threadpool_add_job(pool, work, "10");
    threadpool_add_job(pool, work, "11");
    threadpool_add_job(pool, work, "12");
    threadpool_add_job(pool, work, "13");
    threadpool_add_job(pool, work, "14");
    threadpool_add_job(pool, work, "15");
    threadpool_add_job(pool, work, "16");
    threadpool_add_job(pool, work, "17");
    threadpool_add_job(pool, work, "18");
    threadpool_add_job(pool, work, "19");
    threadpool_add_job(pool, work, "20");
    threadpool_add_job(pool, work, "21");
    threadpool_add_job(pool, work, "22");
    threadpool_add_job(pool, work, "23");
    threadpool_add_job(pool, work, "24");
    threadpool_add_job(pool, work, "25");
    threadpool_add_job(pool, work, "26");
    threadpool_add_job(pool, work, "27");
    threadpool_add_job(pool, work, "28");
    threadpool_add_job(pool, work, "29");
    threadpool_add_job(pool, work, "30");
    threadpool_add_job(pool, work, "31");
    threadpool_add_job(pool, work, "32");
    threadpool_add_job(pool, work, "33");
    threadpool_add_job(pool, work, "34");
    threadpool_add_job(pool, work, "35");
    threadpool_add_job(pool, work, "36");
    threadpool_add_job(pool, work, "37");
    threadpool_add_job(pool, work, "38");
    threadpool_add_job(pool, work, "39");
    threadpool_add_job(pool, work, "40");

    sleep(5);
    threadpool_destroy(pool);
    return 0;
}

struct job
{
    void* (*callback_function)(void *arg);    //线程回调函数
    void *arg;                                //回调函数参数
    struct job *next;
};

struct threadpool
{
    int thread_num;                   //线程池中开启线程的个数
    int queue_max_num;                //队列中最大job的个数
    struct job *head;                 //指向job的头指针
    struct job *tail;                 //指向job的尾指针
    pthread_t *pthreads;              //线程池中所有线程的pthread_t
    pthread_mutex_t mutex;            //互斥信号量
    pthread_cond_t queue_empty;       //队列为空的条件变量
    pthread_cond_t queue_not_empty;   //队列不为空的条件变量
    pthread_cond_t queue_not_full;    //队列不为满的条件变量
    int queue_cur_num;                //队列当前的job个数
    int queue_close;                  //队列是否已经关闭
    int pool_close;                   //线程池是否已经关闭
};

//================================================================================================
//函数名：                   threadpool_init
//函数描述：                 初始化线程池
//输入：                    [in] thread_num     线程池开启的线程个数
//                         [in] queue_max_num  队列的最大job个数
//输出：                    无
//返回：                    成功：线程池地址 失败：NULL
//================================================================================================
struct threadpool* threadpool_init(int thread_num, int queue_max_num);

//================================================================================================
//函数名：                    threadpool_add_job
//函数描述：                  向线程池中添加任务
//输入：                     [in] pool                  线程池地址
//                          [in] callback_function     回调函数
//                          [in] arg                     回调函数参数
//输出：                     无
//返回：                     成功：0 失败：-1
//================================================================================================
int threadpool_add_job(struct threadpool *pool, void* (*callback_function)(void *arg), void *arg);

//================================================================================================
//函数名：                    threadpool_destroy
//函数描述：                   销毁线程池
//输入：                      [in] pool                  线程池地址
//输出：                      无
//返回：                      成功：0 失败：-1
//================================================================================================
int threadpool_destroy(struct threadpool *pool);

//================================================================================================
//函数名：                    threadpool_function
//函数描述：                  线程池中线程函数
//输入：                     [in] arg                  线程池地址
//输出：                     无  
//返回：                     无
//================================================================================================
void* threadpool_function(void* arg);

#include "threadpool.h"

struct threadpool* threadpool_init(int thread_num, int queue_max_num)
{
    struct threadpool *pool = NULL;
    do
    {
        pool = malloc(sizeof(struct threadpool));
        if (NULL == pool)
        {
            printf("failed to malloc threadpool!\n");
            break;
        }
        pool->thread_num = thread_num;
        pool->queue_max_num = queue_max_num;
        pool->queue_cur_num = 0;
        pool->head = NULL;
        pool->tail = NULL;
        if (pthread_mutex_init(&(pool->mutex), NULL))
        {
            printf("failed to init mutex!\n");
            break;
        }
        if (pthread_cond_init(&(pool->queue_empty), NULL))
        {
            printf("failed to init queue_empty!\n");
            break;
        }
        if (pthread_cond_init(&(pool->queue_not_empty), NULL))
        {
            printf("failed to init queue_not_empty!\n");
            break;
        }
        if (pthread_cond_init(&(pool->queue_not_full), NULL))
        {
            printf("failed to init queue_not_full!\n");
            break;
        }
        pool->pthreads = malloc(sizeof(pthread_t) * thread_num);
        if (NULL == pool->pthreads)
        {
            printf("failed to malloc pthreads!\n");
            break;
        }
        pool->queue_close = 0;
        pool->pool_close = 0;
        int i;
        for (i = 0; i < pool->thread_num; ++i)
        {
            pthread_create(&(pool->pthreads[i]), NULL, threadpool_function, (void *)pool);
        }
        
        return pool;    
    } while (0);
    
    return NULL;
}

int threadpool_add_job(struct threadpool* pool, void* (*callback_function)(void *arg), void *arg)
{
    assert(pool != NULL);
    assert(callback_function != NULL);
    assert(arg != NULL);

    pthread_mutex_lock(&(pool->mutex));
    while ((pool->queue_cur_num == pool->queue_max_num) && !(pool->queue_close || pool->pool_close))
    {
        pthread_cond_wait(&(pool->queue_not_full), &(pool->mutex));   //队列满的时候就等待
    }
    if (pool->queue_close || pool->pool_close)    //队列关闭或者线程池关闭就退出
    {
        pthread_mutex_unlock(&(pool->mutex));
        return -1;
    }
    struct job *pjob =(struct job*) malloc(sizeof(struct job));
    if (NULL == pjob)
    {
        pthread_mutex_unlock(&(pool->mutex));
        return -1;
    }
    pjob->callback_function = callback_function;    
    pjob->arg = arg;
    pjob->next = NULL;
    if (pool->head == NULL)   
    {
        pool->head = pool->tail = pjob;
        pthread_cond_broadcast(&(pool->queue_not_empty));  //队列空的时候，有任务来时就通知线程池中的线程：队列非空
    }
    else
    {
        pool->tail->next = pjob;
        pool->tail = pjob;    
    }
    pool->queue_cur_num++;
    pthread_mutex_unlock(&(pool->mutex));
    return 0;
}

void* threadpool_function(void* arg)
{
    struct threadpool *pool = (struct threadpool*)arg;
    struct job *pjob = NULL;
    while (1)  //死循环
    {
        pthread_mutex_lock(&(pool->mutex));
        while ((pool->queue_cur_num == 0) && !pool->pool_close)   //队列为空时，就等待队列非空
        {
            pthread_cond_wait(&(pool->queue_not_empty), &(pool->mutex));
        }
        if (pool->pool_close)   //线程池关闭，线程就退出
        {
            pthread_mutex_unlock(&(pool->mutex));
            pthread_exit(NULL);
        }
        pool->queue_cur_num--;
        pjob = pool->head;
        if (pool->queue_cur_num == 0)
        {
            pool->head = pool->tail = NULL;
        }
        else
        {
            pool->head = pjob->next;
        }
        if (pool->queue_cur_num == 0)
        {
            pthread_cond_signal(&(pool->queue_empty));        //队列为空，就可以通知threadpool_destroy函数，销毁线程函数
        }
        if (pool->queue_cur_num == pool->queue_max_num - 1)
        {
            pthread_cond_broadcast(&(pool->queue_not_full));  //队列非满，就可以通知threadpool_add_job函数，添加新任务
        }
        pthread_mutex_unlock(&(pool->mutex));
        
        (*(pjob->callback_function))(pjob->arg);   //线程真正要做的工作，回调函数的调用
        free(pjob);
        pjob = NULL;    
    }
}
int threadpool_destroy(struct threadpool *pool)
{
    assert(pool != NULL);
    pthread_mutex_lock(&(pool->mutex));
    if (pool->queue_close || pool->pool_close)   //线程池已经退出了，就直接返回
    {
        pthread_mutex_unlock(&(pool->mutex));
        return -1;
    }
    
    pool->queue_close = 1;        //置队列关闭标志
    while (pool->queue_cur_num != 0)
    {
        pthread_cond_wait(&(pool->queue_empty), &(pool->mutex));  //等待队列为空
    }    
    
    pool->pool_close = 1;      //置线程池关闭标志
    pthread_mutex_unlock(&(pool->mutex));
    pthread_cond_broadcast(&(pool->queue_not_empty));  //唤醒线程池中正在阻塞的线程
    pthread_cond_broadcast(&(pool->queue_not_full));   //唤醒添加任务的threadpool_add_job函数
    int i;
    for (i = 0; i < pool->thread_num; ++i)
    {
        pthread_join(pool->pthreads[i], NULL);    //等待线程池的所有线程执行完毕
    }
    
    pthread_mutex_destroy(&(pool->mutex));          //清理资源
    pthread_cond_destroy(&(pool->queue_empty));
    pthread_cond_destroy(&(pool->queue_not_empty));   
    pthread_cond_destroy(&(pool->queue_not_full));    
    free(pool->pthreads);
    struct job *p;
    while (pool->head != NULL)
    {
        p = pool->head;
        pool->head = p->next;
        free(p);
    }
    free(pool);
    return 0;
}

在什么情况下使用线程池？

    1.单个任务处理的时间比较短
    2.将需处理的任务的数量大

    使用线程池的好处:

    1.减少在创建和销毁线程上所花的时间以及系统资源的开销
    2.如不使用线程池，有可能造成系统创建大量线程而导致消耗完系统内存以及”过度切换”。

函数原型：int   pthread_cond_wait(pthread_cond_t   *cond,   pthread_mutex_t   *mutex)  

参数: cond 条件变量  mutex 互斥锁
第一个参数*cond是指向一个条件变量的指针。第二个参数*mutex则是对相关的互斥锁的指针

pthread_cond_wait(&cond,&mutex)操作有两步，是原子操作：第一 解锁，先解除之前的pthread_mutex_lock锁定的mutex；第二 挂起，阻塞并在等待对列里休眠
pthread_cond_signal同样由两个 原子操作：1,解锁;2,发送信号
调用pthread_cond_wait的线程被叫醒之后,将重新锁定mymutex,之后才返回。

下面画个图来表示一下期间锁的调用(是伪码)

lock(mutex)   ----------------a.lock
pthread_cond_wait()
{
    unlock(mutex)-------------a.unlock
    if ( 条件不满足)
      睡觉
    else
    {
      lock(mutex)-------------b.lock
      return
    }
}

dosomething();

unlock(mutex);---------------b.unlock
---------------------  
作者：谢谢考拉  
来源：CSDN  
原文：https://blog.csdn.net/hou512504317/article/details/50875321?utm_source=copy  
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