什麼時候需要創建線程池呢?簡單的說,如果一個應用需要頻繁的創建和銷燬線程,而任務執行的時間又非常短,這樣線程創建和銷燬的帶來的開銷就不容忽視,這時也是線程池該出場的機會了。如果線程創建和銷燬時間相比任務執行時間可以忽略不計,則沒有必要使用線程池了。
下面是Linux系統下用C語言創建的一個線程池。線程池會維護一個任務鏈表(每個CThread_worker結構就是一個任務)。
pool_init()函數預先創建好max_thread_num個線程,每個線程執thread_routine ()函數。該函數中
- while (pool->cur_queue_size == 0)
- {
- pthread_cond_wait (&(pool->queue_ready),&(pool->queue_lock));
- }
表示如果任務鏈表中沒有任務,則該線程出於阻塞等待狀態。否則從隊列中取出任務並執行。
pool_add_worker()函數向線程池的任務鏈表中加入一個任務,加入後通過調用pthread_cond_signal (&(pool->queue_ready))喚醒一個出於阻塞狀態的線程(如果有的話)。
pool_destroy ()函數用於銷燬線程池,線程池任務鏈表中的任務不會再被執行,但是正在運行的線程會一直把任務運行完後再退出。
下面貼出完整代碼
- #include <stdio.h>
- #include <stdlib.h>
- #include <unistd.h>
- #include <sys/types.h>
- #include <pthread.h>
- #include <assert.h>
-
-
-
-
- typedef struct worker
- {
-
- void *(*process) (void *arg);
- void *arg;
- struct worker *next;
- } CThread_worker;
-
- typedef struct
- {
- pthread_mutex_t queue_lock;
- pthread_cond_t queue_ready;
-
- CThread_worker *queue_head;
-
- int shutdown;
- pthread_t *threadid;
-
- int max_thread_num;
-
- 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);
- }
- }
-
- int
- pool_add_worker (void *(*process) (void *arg), void *arg)
- {
-
- CThread_worker *newworker =
- (CThread_worker *) malloc (sizeof (CThread_worker));
- newworker->process = process;
- newworker->arg = arg;
- newworker->next = NULL;
- pthread_mutex_lock (&(pool->queue_lock));
-
- 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));
-
-
- pthread_cond_signal (&(pool->queue_ready));
- return 0;
- }
-
-
- int
- pool_destroy ()
- {
- if (pool->shutdown)
- return -1;
- pool->shutdown = 1;
-
- pthread_cond_broadcast (&(pool->queue_ready));
-
- int i;
- for (i = 0; i < pool->max_thread_num; i++)
- pthread_join (pool->threadid[i], NULL);
- free (pool->threadid);
-
- CThread_worker *head = NULL;
- while (pool->queue_head != NULL)
- {
- head = pool->queue_head;
- pool->queue_head = pool->queue_head->next;
- free (head);
- }
-
- pthread_mutex_destroy(&(pool->queue_lock));
- pthread_cond_destroy(&(pool->queue_ready));
-
- free (pool);
-
- 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));
-
-
- 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));
- }
-
- if (pool->shutdown)
- {
-
- 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 (pool->cur_queue_size != 0);
- assert (pool->queue_head != NULL);
-
-
- pool->cur_queue_size--;
- CThread_worker *worker = pool->queue_head;
- pool->queue_head = worker->next;
- pthread_mutex_unlock (&(pool->queue_lock));
-
- (*(worker->process)) (worker->arg);
- free (worker);
- worker = NULL;
- }
-
- pthread_exit (NULL);
- }
下面是測試代碼
- void *
- myprocess (void *arg)
- {
- printf ("threadid is 0x%x, working on task %d/n", pthread_self (),*(int *) arg);
- sleep (1);
- return NULL;
- }
- int
- main (int argc, char **argv)
- {
- pool_init (3);
-
-
- int *workingnum = (int *) malloc (sizeof (int) * 10);
- int i;
- for (i = 0; i < 10; i++)
- {
- workingnum[i] = i;
- pool_add_worker (myprocess, &workingnum[i]);
- }
-
- sleep (5);
-
- pool_destroy ();
- free (workingnum);
- return 0;
- }
將上述所有代碼放入threadpool.c文件中,
在Linux輸入編譯命令
$ gcc -o threadpool threadpool.c -lpthread
以下是運行結果
starting thread 0xb7df6b90
thread 0xb7df6b90 is waiting
starting thread 0xb75f5b90
thread 0xb75f5b90 is waiting
starting thread 0xb6df4b90
thread 0xb6df4b90 is waiting
thread 0xb7df6b90 is starting to work
threadid is 0xb7df6b90, working on task 0
thread 0xb75f5b90 is starting to work
threadid is 0xb75f5b90, working on task 1
thread 0xb6df4b90 is starting to work
threadid is 0xb6df4b90, working on task 2
thread 0xb7df6b90 is starting to work
threadid is 0xb7df6b90, working on task 3
thread 0xb75f5b90 is starting to work
threadid is 0xb75f5b90, working on task 4
thread 0xb6df4b90 is starting to work
threadid is 0xb6df4b90, working on task 5
thread 0xb7df6b90 is starting to work
threadid is 0xb7df6b90, working on task 6
thread 0xb75f5b90 is starting to work
threadid is 0xb75f5b90, working on task 7
thread 0xb6df4b90 is starting to work
threadid is 0xb6df4b90, working on task 8
thread 0xb7df6b90 is starting to work
threadid is 0xb7df6b90, working on task 9
thread 0xb75f5b90 is waiting
thread 0xb6df4b90 is waiting
thread 0xb7df6b90 is waiting
thread 0xb75f5b90 will exit
thread 0xb6df4b90 will exit
thread 0xb7df6b90 will exit