pool_init()函式預先建立好max_thread_num個執行緒，每個執行緒執thread_routine ()函式。該函式中

1. while (pool->cur_queue_size == 0)
2. {
3.        pthread_cond_wait (&(pool->queue_ready),&(pool->queue_lock));
4. }

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. *執行緒池裡所有執行和等待的任務都是一個CThread_worker
9. *由於所有任務都在連結串列裡，所以是一個連結串列結構
10. */
11. typedef struct worker
12. {
13.     /*回撥函式，任務執行時會呼叫此函式，注意也可宣告成其它形式*/
14.     void *(*process) (void *arg);
15.     void *arg;/*回撥函式的引數*/
16.     struct worker *next;
17. } CThread_worker;
18. /*執行緒池結構*/
19. typedef struct
20. {
21.      pthread_mutex_t queue_lock;
22.      pthread_cond_t queue_ready;
23.     /*連結串列結構，執行緒池中所有等待任務*/
24.      CThread_worker *queue_head;
25.     /*是否銷燬執行緒池*/
26.     int shutdown;
27.      pthread_t *threadid;
28.     /*執行緒池中允許的活動執行緒數目*/
29.     int max_thread_num;
30.     /*當前等待佇列的任務數目*/
31.     int cur_queue_size;
32. } CThread_pool;
33. int pool_add_worker (void *(*process) (void *arg), void *arg);
34. void *thread_routine (void *arg);
35. static CThread_pool *pool = NULL;
36. void
37. pool_init (int max_thread_num)
38. {
39.      pool = (CThread_pool *) malloc (sizeof (CThread_pool));
40.      pthread_mutex_init (&(pool->queue_lock), NULL);
41.      pthread_cond_init (&(pool->queue_ready), NULL);
42.      pool->queue_head = NULL;
43.      pool->max_thread_num = max_thread_num;
44.      pool->cur_queue_size = 0;
45.      pool->shutdown = 0;
46.      pool->threadid =
47.          (pthread_t *) malloc (max_thread_num * sizeof (pthread_t));
48.     int i = 0;
49.     for (i = 0; i < max_thread_num; i++)
50.      {
51.          pthread_create (&(pool->threadid[i]), NULL, thread_routine,
52.                  NULL);
53.      }
54. }
55. /*向執行緒池中加入任務*/
56. int
57. pool_add_worker (void *(*process) (void *arg), void *arg)
58. {
59.     /*構造一個新任務*/
60.      CThread_worker *newworker =
61.          (CThread_worker *) malloc (sizeof (CThread_worker));
62.      newworker->process = process;
63.      newworker->arg = arg;
64.      newworker->next = NULL;/*別忘置空*/
65.      pthread_mutex_lock (&(pool->queue_lock));
66.     /*將任務加入到等待佇列中*/
67.      CThread_worker *member = pool->queue_head;
68.     if (member != NULL)
69.      {
70.         while (member->next != NULL)
71.              member = member->next;
72.          member->next = newworker;
73.      }
74.     else
75.      {
76.          pool->queue_head = newworker;
77.      }
78.      assert (pool->queue_head != NULL);
79.      pool->cur_queue_size++;
80.      pthread_mutex_unlock (&(pool->queue_lock));
81.     /*好了，等待佇列中有任務了，喚醒一個等待執行緒；
82.      注意如果所有執行緒都在忙碌，這句沒有任何作用*/
83.      pthread_cond_signal (&(pool->queue_ready));
84.     return 0;
85. }
86. /*銷燬執行緒池，等待佇列中的任務不會再被執行，但是正在執行的執行緒會一直
87. 把任務執行完後再退出*/
88. int
89. pool_destroy ()
90. {
91.     if (pool->shutdown)
92.         return -1;/*防止兩次呼叫*/
93.      pool->shutdown = 1;
94.     /*喚醒所有等待執行緒，執行緒池要銷燬了*/
95.      pthread_cond_broadcast (&(pool->queue_ready));
96.     /*阻塞等待執行緒退出，否則就成殭屍了*/
97.     int i;
98.     for (i = 0; i < pool->max_thread_num; i++)
99.          pthread_join (pool->threadid[i], NULL);
100.      free (pool->threadid);
101.     /*銷燬等待佇列*/
102.      CThread_worker *head = NULL;
103.     while (pool->queue_head != NULL)
104.      {
105.          head = pool->queue_head;
106.          pool->queue_head = pool->queue_head->next;
107.          free (head);
108.      }
109.     /*條件變數和互斥量也別忘了銷燬*/
110.      pthread_mutex_destroy(&(pool->queue_lock));
111.      pthread_cond_destroy(&(pool->queue_ready));
112.      free (pool);
113.     /*銷燬後指標置空是個好習慣*/
114.      pool=NULL;
115.     return 0;
116. }
117. void *
118. thread_routine (void *arg)
119. {
120.      printf ("starting thread 0x%x\n", pthread_self ());
121.     while (1)
122.      {
123.          pthread_mutex_lock (&(pool->queue_lock));
124.         /*如果等待佇列為0並且不銷燬執行緒池，則處於阻塞狀態; 注意
125.          pthread_cond_wait是一個原子操作，等待前會解鎖，喚醒後會加鎖*/
126.         while (pool->cur_queue_size == 0 && !pool->shutdown)
127.          {
128.              printf ("thread 0x%x is waiting\n", pthread_self ());
129.              pthread_cond_wait (&(pool->queue_ready), &(pool->queue_lock));
130.          }
131.         /*執行緒池要銷燬了*/
132.         if (pool->shutdown)
133.          {
134.             /*遇到break,continue,return等跳轉語句，千萬不要忘記先解鎖*/
135.              pthread_mutex_unlock (&(pool->queue_lock));
136.              printf ("thread 0x%x will exit\n", pthread_self ());
137.              pthread_exit (NULL);
138.          }
139.          printf ("thread 0x%x is starting to work\n", pthread_self ());
140.         /*assert是除錯的好幫手*/
141.          assert (pool->cur_queue_size != 0);
142.          assert (pool->queue_head != NULL);
143.         /*等待佇列長度減去1，並取出連結串列中的頭元素*/
144.          pool->cur_queue_size--;
145.          CThread_worker *worker = pool->queue_head;
146.          pool->queue_head = worker->next;
147.          pthread_mutex_unlock (&(pool->queue_lock));
148.         /*呼叫回撥函式，執行任務*/
149.          (*(worker->process)) (worker->arg);
150.          free (worker);
151.          worker = NULL;
152.      }
153.     /*這一句應該是不可達的*/
154.      pthread_exit (NULL);
155. }

1. void *
2. myprocess (void *arg)
3. {
4.      printf ("threadid is 0x%x, working on task %d\n", pthread_self (),*(int *) arg);
5.      sleep (1);/*休息一秒，延長任務的執行時間*/
6.     return NULL;
7. }
8. int
9. main (int argc, char **argv)
10. {
11.      pool_init (3);/*執行緒池中最多三個活動執行緒*/
12.     /*連續向池中投入10個任務*/
13.     int *workingnum = (int *) malloc (sizeof (int) * 10);
14.     int i;
15.     for (i = 0; i < 10; i++)
16.      {
17.          workingnum[i] = i;
18.          pool_add_worker (myprocess, &workingnum[i]);
19.      }
20.     /*等待所有任務完成*/
21.      sleep (5);
22.     /*銷燬執行緒池*/
23.      pool_destroy ();
24.      free (workingnum);
25.     return 0;
26. }