基于条件变量的一个线程池实现

#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);
}


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;
}