线程池的实现

  1 #include <stdio.h>
  2 #include <stdlib.h>
  3 #include <unistd.h>
  4 #include <sys/types.h>
  5 #include <pthread.h>
  6 #include <assert.h>
  7 
  8 /*
  9  *线程池里所有运行和等待的任务都是一个CThread_worker
 10  *由于所有任务都在链表里，所以是一个链表结构
 11  */
 12 typedef struct worker
 13 {
 14     /*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*/
 15     void *(*process) (void *arg);
 16     void *arg;/*回调函数的参数*/
 17     struct worker *next;
 18 
 19 } CThread_worker;
 20 
 21 
 22 
 23 /*线程池结构*/
 24 typedef struct CThread_pool
 25 {
 26     pthread_mutex_t queue_lock;
 27     pthread_cond_t queue_ready;
 28 
 29     /*链表结构，线程池中所有等待任务*/
 30     CThread_worker *queue_head;
 31 
 32     /*是否销毁线程池*/
 33     int shutdown;
 34     pthread_t *threadid;
 35     /*线程池中允许的活动线程数目*/
 36     int max_thread_num;
 37     /*当前等待队列的任务数目*/
 38     int cur_queue_size;
 39 
 40 } CThread_pool;
 41 
 42 
 43 
 44 int pool_add_worker (void *(*process) (void *arg), void *arg);
 45 void *thread_routine (void *arg);
 46 
 47 
 48 //share resource
 49 static CThread_pool *pool = NULL;
 50 
 51 void pool_init (int max_thread_num)
 52 {
 53     pool = (CThread_pool *) malloc (sizeof (CThread_pool));
 54 
 55     /*线程同步，初始化信号量和条件变量*/
 56     pthread_mutex_init (&(pool->queue_lock), NULL);
 57     pthread_cond_init (&(pool->queue_ready), NULL);
 58 
 59     pool->queue_head = NULL;
 60 
 61     pool->max_thread_num = max_thread_num;
 62     pool->cur_queue_size = 0;
 63 
 64     pool->shutdown = 0;
 65 
 66     pool->threadid = (pthread_t *) malloc (max_thread_num * sizeof (pthread_t));
 67     int i = 0;
 68     for (i = 0; i < max_thread_num; i++)
 69     { 
 70         pthread_create (&(pool->threadid[i]), NULL, thread_routine, NULL);
 71     }
 72 }
 73 
 74 
 75 
 76 /*向线程池中加入任务*/
 77 int pool_add_worker (void *(*process) (void *arg), void *arg)
 78 {
 79     /*构造一个新任务*/
 80     CThread_worker *newworker = (CThread_worker *) malloc (sizeof (CThread_worker));
 81     newworker->process = process;
 82     newworker->arg = arg;
 83     newworker->next = NULL;/*别忘置空*/
 84 
 85     pthread_mutex_lock (&(pool->queue_lock));
 86     /*将任务加入到等待队列中*/
 87     CThread_worker *member = pool->queue_head;
 88     if (member != NULL)
 89     {
 90         while (member->next != NULL)
 91             member = member->next;
 92         member->next = newworker;
 93     }
 94     else
 95     {
 96         pool->queue_head = newworker;
 97     }
 98 
 99     assert (pool->queue_head != NULL);
100 
101     pool->cur_queue_size++;
102     pthread_mutex_unlock (&(pool->queue_lock));
103     /*好了，等待队列中有任务了，唤醒一个等待线程；
104       注意如果所有线程都在忙碌，这句没有任何作用*/
105     pthread_cond_signal (&(pool->queue_ready));
106     return 0;
107 }
108 
109 
110 
111 /*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
112   把任务运行完后再退出*/
113     int
114 pool_destroy ()
115 {
116     if (pool->shutdown)
117         return -1;/*防止两次调用*/
118     pool->shutdown = 1;
119 
120     /*唤醒所有等待线程，线程池要销毁了*/
121     pthread_cond_broadcast (&(pool->queue_ready));
122 
123     /*阻塞等待线程退出，否则就成僵尸了*/
124     int i;
125     for (i = 0; i < pool->max_thread_num; i++)
126         pthread_join (pool->threadid[i], NULL);
127     free (pool->threadid);
128 
129     /*销毁等待队列*/    
130     CThread_worker *head = NULL;
131     while (pool->queue_head != NULL)
132     {
133         head = pool->queue_head;
134         pool->queue_head = pool->queue_head->next;
135         free (head);
136     }
137     /*条件变量和互斥量也别忘了销毁*/
138     pthread_mutex_destroy(&(pool->queue_lock));
139     pthread_cond_destroy(&(pool->queue_ready));
140 
141     free (pool);
142     /*销毁后指针置空是个好习惯*/
143     pool=NULL;
144     return 0;
145 }
146 
147 
148 
149 void * thread_routine (void *arg)
150 {
151     printf ("starting thread %u\n", (unsigned int)pthread_self ());
152     while (1)
153     {
154         pthread_mutex_lock (&(pool->queue_lock));
155         /*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
156           pthread_cond_wait是一个原子操作，等待前会解锁，唤醒后会加锁*/
157         while (pool->cur_queue_size == 0 && !pool->shutdown)
158         {
159             printf ("thread %u is waiting\n", (unsigned int)pthread_self ());
160             pthread_cond_wait (&(pool->queue_ready), &(pool->queue_lock));
161         }
162 
163         /*线程池要销毁了*/
164         if (pool->shutdown)
165         {
166             /*遇到break,continue,return等跳转语句，千万不要忘记先解锁*/
167             pthread_mutex_unlock (&(pool->queue_lock));
168             printf ("thread %u will exit\n", (unsigned int)pthread_self ());
169             pthread_exit (NULL);
170         }
171 
172         printf ("thread %u is starting to work\n", (unsigned int)pthread_self ());
173 
174         /*assert是调试的好帮手*/
175         assert (pool->cur_queue_size != 0);
176         assert (pool->queue_head != NULL);
177 
178         /*等待队列长度减去1，并取出链表中的头元素*/
179         pool->cur_queue_size--;
180         CThread_worker *worker = pool->queue_head;
181         pool->queue_head = worker->next;
182         pthread_mutex_unlock (&(pool->queue_lock));
183 
184         /*调用回调函数，执行任务*/
185         (*(worker->process)) (worker->arg);
186         free (worker);
187         worker = NULL;
188     }
189     /*这一句应该是不可达的*/
190     pthread_exit (NULL);
191 }
192 
193 //    下面是测试代码
194 
195 void * myprocess (void *arg)
196 {
197     printf ("threadid is %u, working on task %d\n", (unsigned int)pthread_self (),  *(int *) arg);
198     sleep (1);/*休息一秒，延长任务的执行时间*/
199     return NULL;
200 }
201 
202     int
203 main (int argc, char **argv)
204 {
205     pool_init (3);/*线程池中最多三个活动线程*/
206 
207     /*连续向池中投入10个任务*/
208     int *workingnum = (int *) malloc (sizeof (int) * 10);
209     int i;
210     for (i = 0; i < 10; i++)
211     {
212         workingnum[i] = i;
213 //        pool_add_worker (myprocess, &workingnum[i]);
214     }
215     /*等待所有任务完成*/
216     sleep (5);
217     /*销毁线程池*/
218     pool_destroy ();
219 
220     free (workingnum);
221     return 0;
222 }