线程池的理解与简单实现

#include <stdio.h>  
#include <stdlib.h>  
#include <unistd.h>  
#include <sys/types.h>  
#include <pthread.h>  
#include <assert.h>  

/* 
*线程池里所有运行和等待的任务都是一个CThread_worker 
*由于所有任务都在链表里，所以是一个链表结构 
*/  
typedef struct worker  
{  
    /*回调函数，任务运行时会调用此函数，注意也可声明成其它形式*/  
    void *(*process) (void *arg);  
    void *arg;/*回调函数的参数*/  
    struct worker *next;    
} CThread_worker;  

/*线程池结构*/  
typedef struct  
{  
    pthread_mutex_t queue_lock;  
    pthread_cond_t queue_ready;  

    /*链表结构，线程池中所有等待任务*/  
    CThread_worker *queue_head;  

    /*是否销毁线程池*/  
    int shutdown;  
    pthread_t *threadid;  
    /*线程池中允许的活动线程数目*/  
    int max_thread_num;  
    /*当前等待队列的任务数目*/  
    int cur_queue_size;  

} CThread_pool;  


int pool_add_worker (void *(*process) (void *arg), void *arg);  
void *thread_routine (void *arg);  


static CThread_pool *pool = NULL;  
void pool_init (int max_thread_num)  
{  
    pool = (CThread_pool *) malloc (sizeof (CThread_pool));  

    pthread_mutex_init (&(pool->queue_lock), NULL);  
    pthread_cond_init (&(pool->queue_ready), NULL);  

    pool->queue_head = NULL;  

    pool->max_thread_num = max_thread_num;  
    pool->cur_queue_size = 0;  

    pool->shutdown = 0;  

    pool->threadid = (pthread_t *) malloc (max_thread_num * sizeof (pthread_t));  
    int i = 0;  
    for (i = 0; i < max_thread_num; i++)  
    {   
        pthread_create (&(pool->threadid[i]), NULL, thread_routine,NULL);  
    }  
}  



/*向线程池中加入任务*/  
int pool_add_worker (void *(*process) (void *arg), void *arg)  
{  
    /*构造一个新任务*/  
    CThread_worker *newworker = (CThread_worker *) malloc (sizeof (CThread_worker));  
    newworker->process = process;  
    newworker->arg = arg;  
    newworker->next = NULL;/*别忘置空*/  

    pthread_mutex_lock (&(pool->queue_lock));  
    /*将任务加入到等待队列中*/  
    CThread_worker *member = pool->queue_head;  
    if (member != NULL)  
    {  
        while (member->next != NULL)  
            member = member->next;  
        member->next = newworker;  
    }  
    else  
    {  
        pool->queue_head = newworker;  
    }  

    assert (pool->queue_head != NULL);  

    pool->cur_queue_size++;  
    pthread_mutex_unlock (&(pool->queue_lock));  
    /*好了，等待队列中有任务了，唤醒一个等待线程； 
    注意如果所有线程都在忙碌，这句没有任何作用*/  
    pthread_cond_signal (&(pool->queue_ready));  
    return 0;  
}  



/*销毁线程池，等待队列中的任务不会再被执行，但是正在运行的线程会一直 
把任务运行完后再退出*/  
int pool_destroy ()  
{  
    if (pool->shutdown)  
        return -1;/*防止两次调用*/  
    pool->shutdown = 1;  

    /*唤醒所有等待线程，线程池要销毁了*/  
    pthread_cond_broadcast (&(pool->queue_ready));  

    /*阻塞等待线程退出，否则就成僵尸了*/  
    int i;  
    for (i = 0; i < pool->max_thread_num; i++)  
        pthread_join (pool->threadid[i], NULL);  
    free (pool->threadid);  

    /*销毁等待队列*/  
    CThread_worker *head = NULL;  
    while (pool->queue_head != NULL)  
    {  
        head = pool->queue_head;  
        pool->queue_head = pool->queue_head->next;  
        free (head);  
    }  
    /*条件变量和互斥量也别忘了销毁*/  
    pthread_mutex_destroy(&(pool->queue_lock));  
    pthread_cond_destroy(&(pool->queue_ready));  

    free (pool);  
    /*销毁后指针置空是个好习惯*/  
    pool=NULL;  
    return 0;  
}  



void * thread_routine (void *arg)  
{  
    printf ("starting thread 0x%x\n", pthread_self ());  
    while (1)  
    {  
        pthread_mutex_lock (&(pool->queue_lock));  
        /*如果等待队列为0并且不销毁线程池，则处于阻塞状态; 注意 
        pthread_cond_wait是一个原子操作，等待前会解锁，唤醒后会加锁*/  
        while (pool->cur_queue_size == 0 && !pool->shutdown)  
        {  
            printf ("thread 0x%x is waiting\n", pthread_self ());  
            pthread_cond_wait (&(pool->queue_ready), &(pool->queue_lock));  
        }  

        /*线程池要销毁了*/  
        if (pool->shutdown)  
        {  
            /*遇到break,continue,return等跳转语句，千万不要忘记先解锁*/  
            pthread_mutex_unlock (&(pool->queue_lock));  
            printf ("thread 0x%x will exit\n", pthread_self ());  
            pthread_exit (NULL);  
        }  

        printf ("thread 0x%x is starting to work\n", pthread_self ());  

        /*assert是调试的好帮手*/  
        assert (pool->cur_queue_size != 0);  
        assert (pool->queue_head != NULL);  

        /*等待队列长度减去1，并取出链表中的头元素*/  
        pool->cur_queue_size--;  
        CThread_worker *worker = pool->queue_head;  
        pool->queue_head = worker->next;  
        pthread_mutex_unlock (&(pool->queue_lock));  

        /*调用回调函数，执行任务*/  
        (*(worker->process)) (worker->arg);  
        free (worker);  
        worker = NULL;  
    }  
    /*这一句应该是不可达的*/  
    pthread_exit (NULL);  
}  

//    下面是测试代码  

void * myprocess (void *arg)  
{  
    printf ("threadid is 0x%x, working on task %d\n", pthread_self (),*(int *) arg);  
    sleep (1);/*休息一秒，延长任务的执行时间*/  
    return NULL;  
}  

int main (int argc, char **argv)  
{  
    pool_init (3);/*线程池中最多三个活动线程*/  

    /*连续向池中投入10个任务*/  
    int *workingnum = (int *) malloc (sizeof (int) * 10);  
    int i;  
    for (i = 0; i < 10; i++)  
    {  
        workingnum[i] = i;  
        pool_add_worker (myprocess, &workingnum[i]);  
    }  
    /*等待所有任务完成*/  
    sleep (5);  
    /*销毁线程池*/  
    pool_destroy ();  

    free (workingnum);  
    return 0;  
}