Linux下用C实现线程池
什么时候需要创建线程池呢?简单的说,如果一个应用需要频繁的创建和销毁线程,而任务执行的时间又非常短,这样线程创建和销毁的带来的开销就不容忽视,这时也是线程池该出场的机会了。如果线程创建和销毁时间相比任务执行时间可以忽略不计,则没有必要使用线程池了。
下面是Linux系统下用C语言创建的一个线程池。线程池会维护一个任务链表(每个CThread_worker结构就是一个任务)。
pool_init()函数预先创建好max_thread_num个线程,每个线程执thread_routine ()函数。该函数中
while (pool->cur_queue_size == 0) { pthread_cond_wait (&(pool->queue_ready),&(pool->queue_lock)); }
表示如果任务链表中没有任务,则该线程出于阻塞等待状态。否则从队列中取出任务并执行。
pool_add_worker()函数向线程池的任务链表中加入一个任务,加入后通过调用pthread_cond_signal (&(pool->queue_ready))唤醒一个出于阻塞状态的线程(如果有的话)。
pool_destroy ()函数用于销毁线程池,线程池任务链表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。
以下为详细的实现代码:
#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; }
将上述所有代码放入threadpool.c文件中,
在Linux输入编译命令
$ gcc -o threadpool threadpool.c -lpthread
原文地址:http://hi.baidu.com/lifepath/blog/item/0eb8ea5d6321c244fbf2c0d0.html
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