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Linux系统线程池的示例分析，针对这个问题，这篇文章详细介绍了相对应的分析和解答，希望可以帮助更多想解决这个问题的小伙伴找到更简单易行的方法。
程序启动之前，创建一定数量的线程，放入空闲的队列中，初始化线程池。
这些线程均处于阻塞状态，只占一点内存，不占用cpu。
当任务到达就从线程池中取出一个空闲线程，将任务传入此线程中运行。
当所有的线程都处在处理任务的时候，线程池将自动创建一定数量的新线程，用于处理更多的任务。
执行完任务的线程也并不退出，而是继续在线程池中等待下一次任务。
但大部分线程处于阻塞状态时，线程池将自动销毁一部分线程，回收系统资源。
线程管理器
用于创建并管理线程池。
工作线程
线程池中实际执行任务的线程。在初始化线程时会预先创建好固定数目的线程在池中，这些初始化的线程一般处于空闲状态，一般不占用CPU，占用较小的内存空间。
任务接口
每个任务必须实现的接口，当线程池的任务队列中有可执行任务时，被空闲的工作线程调去执行，把任务抽象出来形成接口，可以做到线程池与具体的任务无关。
任务队列
用来存放没有处理的任务，提供一种缓冲机制
实现这种结构有好几种方法，常用的是队列，主要运用先进先出原理，另外一种是链表之类的数据结构，可以动态的为它分配内存空间，应用中比较灵活
程序由三个文件组成，分别是thread_pool.h, thread_pool.c和test.c组成。
thread_pool.h如下：
#include
struct job {
void * (*callback_function)(void *arg);
void *arg;
struct job *next;
};
struct threadpool {
int thread_num;
int queue_max_num;
struct job *head;
struct job *tail;
pthread_t *pthreads;
pthread_mutex_t mutex;
pthread_cond_t queue_empty;
pthread_cond_t queue_not_empty;
pthread_cond_t queue_not_full;
int queue_cur_num;
int queue_close;
int pool_close;
};
struct threadpool *threadpool_init(int thread_num, int queue_max_num);
int threadpool_add_job(struct threadpool *pool, void *(*callback_function)(void *arg), void *arg);
int threadpool_destroy(struct threadpool *pool);
void *threadpool_function(void *arg);
123456789101112131415161718192021222324252627282930thread_pool.c如下：
#include #include #include
#include "thread_pool.h"
struct threadpool *threadpool_init(int thread_num, int queue_max_num)
{
struct threadpool *pool = NULL;
do {
pool = (struct threadpool *)calloc(1, sizeof(struct threadpool));
if (!pool) {
printf("calloc error: %m\n");
break;
}
pool->thread_num = thread_num;
pool->queue_max_num = queue_max_num;
pool->queue_cur_num = 0;
pool->head = NULL;
pool->tail = NULL;
if (pthread_mutex_init(&(pool->mutex), NULL)) {
printf("init mutex error: %m\n");
break;
}
if (pthread_cond_init(&(pool->queue_empty), NULL)) {
printf("init queue_empty error: %m\n");
break;
}
if (pthread_cond_init(&(pool->queue_not_empty), NULL)) {
printf("init queue_not_empty error: %m\n");
break;
}
if (pthread_cond_init(&(pool->queue_not_full), NULL)) {
printf("init queue_not_full error: %m\n");
break;
}
pool->pthreads = calloc(1, sizeof(pthread_t) * thread_num);
if (!pool->pthreads) {
printf("calloc pthreads error: %m\n");
break;
}
pool->queue_close = 0;
pool->pool_close = 0;
int i;
for (i = 0; i thread_num; i++) {
pthread_create(&(pool->pthreads[i]), NULL, threadpool_function, (void *)pool);
}
return pool;
} while (0);
return NULL;
}
int threadpool_add_job(struct threadpool *pool, void *(*callback_function)(void *arg), void *arg)
{
assert(pool != NULL);
assert(callback_function != NULL);
assert(arg != NULL);
pthread_mutex_lock(&(pool->mutex));
while ((pool->queue_cur_num == pool->queue_max_num) && !(pool->queue_close || pool->pool_close)) {
pthread_cond_wait(&(pool->queue_not_full), &(pool->mutex));
}
if (pool->queue_close || pool->pool_close) {
pthread_mutex_unlock(&(pool->mutex));
return -1;
}
struct job *pjob = (struct job*) calloc(1, sizeof(struct job));
if (!pjob) {
pthread_mutex_unlock(&(pool->mutex));
return -1;
}
pjob->callback_function = callback_function;
pjob->arg = arg;
pjob->next = NULL;
if (pool->head == NULL) {
pool->head = pool->tail = pjob;
pthread_cond_broadcast(&(pool->queue_not_empty));
} else {
pool->tail->next = pjob;
pool->tail = pjob;
}
pool->queue_cur_num++;
pthread_mutex_unlock(&(pool->mutex));
return 0;
}
void *threadpool_function(void *arg)
{
struct threadpool *pool = (struct threadpool *)arg;
struct job *pjob = NULL;
while (1) {
pthread_mutex_lock(&(pool->mutex));
while ((pool->queue_cur_num == 0) && !pool->pool_close) {
pthread_cond_wait(&(pool->queue_not_empty), &(pool->mutex));
}
if (pool->pool_close) {
pthread_mutex_unlock(&(pool->mutex));
pthread_exit(NULL);
}
pool->queue_cur_num--;
pjob = pool->head;
if (pool->queue_cur_num == 0) {
pool->head = pool->tail = NULL;
} else {
pool->head = pjob->next;
}
if (pool->queue_cur_num == 0) {
pthread_cond_signal(&(pool->queue_empty));
}
if (pool->queue_cur_num == pool->queue_max_num - 1) {
pthread_cond_broadcast(&(pool->queue_not_full));
}
pthread_mutex_unlock(&(pool->mutex));
(*(pjob->callback_function))(pjob->arg);
free(pjob);
pjob = NULL;
}
}
int threadpool_destroy(struct threadpool *pool)
{
assert(pool != NULL);
pthread_mutex_lock(&(pool->mutex));
if (pool->queue_close || pool->pool_close) {
pthread_mutex_unlock(&(pool->mutex));
return -1;
}
pool->queue_close = 1;
while (pool->queue_cur_num != 0) {
pthread_cond_wait(&(pool->queue_empty), &(pool->mutex));
}
pool->pool_close = 1;
pthread_mutex_unlock(&(pool->mutex));
pthread_cond_broadcast(&(pool->queue_not_empty));
pthread_cond_broadcast(&(pool->queue_not_full));
int i;
for (i = 0; i thread_num; i++) {
pthread_join(pool->pthreads[i], NULL);
}
pthread_mutex_destroy(&(pool->mutex));
pthread_cond_destroy(&(pool->queue_empty));
pthread_cond_destroy(&(pool->queue_not_empty));
pthread_cond_destroy(&(pool->queue_not_full));
free(pool->pthreads);
struct job *p;
while (pool->head != NULL) {
p = pool->head;
pool->head = p->next;
free(p);
}
free(pool);
return 0;
}
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166test.c用于测试，如下：
#include #include "thread_pool.h"
void* work(void* arg)
{
char *p = (char*) arg;
printf("threadpool callback fuction : %s.\n", p);
sleep(1);
}
int main(void)
{
struct threadpool *pool = threadpool_init(10, 20);
threadpool_add_job(pool, work, "1");
threadpool_add_job(pool, work, "2");
threadpool_add_job(pool, work, "3");
threadpool_add_job(pool, work, "4");
threadpool_add_job(pool, work, "5");
threadpool_add_job(pool, work, "6");
threadpool_add_job(pool, work, "7");
threadpool_add_job(pool, work, "8");
threadpool_add_job(pool, work, "9");
threadpool_add_job(pool, work, "10");
threadpool_add_job(pool, work, "11");
threadpool_add_job(pool, work, "12");
threadpool_add_job(pool, work, "13");
threadpool_add_job(pool, work, "14");
threadpool_add_job(pool, work, "15");
threadpool_add_job(pool, work, "16");
threadpool_add_job(pool, work, "17");
threadpool_add_job(pool, work, "18");
threadpool_add_job(pool, work, "19");
threadpool_add_job(pool, work, "20");
threadpool_add_job(pool, work, "21");
threadpool_add_job(pool, work, "22");
threadpool_add_job(pool, work, "23");
threadpool_add_job(pool, work, "24");
threadpool_add_job(pool, work, "25");
threadpool_add_job(pool, work, "26");
threadpool_add_job(pool, work, "27");
threadpool_add_job(pool, work, "28");
threadpool_add_job(pool, work, "29");
threadpool_add_job(pool, work, "30");
threadpool_add_job(pool, work, "31");
threadpool_add_job(pool, work, "32");
threadpool_add_job(pool, work, "33");
threadpool_add_job(pool, work, "34");
threadpool_add_job(pool, work, "35");
threadpool_add_job(pool, work, "36");
threadpool_add_job(pool, work, "37");
threadpool_add_job(pool, work, "38");
threadpool_add_job(pool, work, "39");
threadpool_add_job(pool, work, "40");
sleep(5);
threadpool_destroy(pool);
return 0;
}
1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859执行如下编译命令： gcc test.c thread_pool.c -lpthread
程序运行结果如下：
-> % ./a.out threadpool callback fuction : 1. threadpool callback fuction : 7. threadpool callback fuction : 8. threadpool callback fuction : 2. threadpool callback fuction : 3. threadpool callback fuction : 4. threadpool callback fuction : 5. threadpool callback fuction : 6. threadpool callback fuction : 9. threadpool callback fuction : 10. threadpool callback fuction : 12. threadpool callback fuction : 16. threadpool callback fuction : 11. threadpool callback fuction : 18. threadpool callback fuction : 14. threadpool callback fuction : 15. threadpool callback fuction : 17. threadpool callback fuction : 13. threadpool callback fuction : 19. threadpool callback fuction : 20. threadpool callback fuction : 21. threadpool callback fuction : 23. threadpool callback fuction : 24. threadpool callback fuction : 22. threadpool callback fuction : 26. threadpool callback fuction : 27. threadpool callback fuction : 28. threadpool callback fuction : 25. threadpool callback fuction : 29. threadpool callback fuction : 30. threadpool callback fuction : 31. threadpool callback fuction : 32. threadpool callback fuction : 33. threadpool callback fuction : 34. threadpool callback fuction : 35. threadpool callback fuction : 36. threadpool callback fuction : 37. threadpool callback fuction : 38. threadpool callback fuction : 39. threadpool callback fuction : 40.
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