大多數的網絡服務器,包括Web服務器都具備一個特色,就是單位時間內必須處理數目巨大的鏈接請求,可是處理時間倒是比較短的。在傳統的多線程服務器模型中是這樣實現的:一旦有個請求到達,就建立一個新的線程,由該線程執行任務,任務執行完畢以後,線程就退出。這就是"即時建立,即時銷燬"的策略。儘管與建立進程相比,建立線程的時間已經大大的縮短,可是若是提交給線程的任務是執行時間較短,並且執行次數很是頻繁,那麼服務器就將處於一個不停的建立線程和銷燬線程的狀態。這筆開銷是不可忽略的,尤爲是線程執行的時間很是很是短的狀況。服務器
線程池就是爲了解決上述問題的,它的實現原理是這樣的:在應用程序啓動以後,就立刻建立必定數量的線程,放入空閒的隊列中。這些線程都是處於阻塞狀態,這些線程只佔一點內存,不佔用CPU。當任務到來後,線程池將選擇一個空閒的線程,將任務傳入此線程中運行。當全部的線程都處在處理任務的時候,線程池將自動建立必定的數量的新線程,用於處理更多的任務。執行任務完成以後線程並不退出,而是繼續在線程池中等待下一次任務。當大部分線程處於阻塞狀態時,線程池將自動銷燬一部分的線程,回收系統資源。網絡
下面例程的思路:程序啓動以前,初始化線程池,啓動線程池中的線程,因爲尚未任務到來,線程池中的全部線程都處在阻塞狀態,當一有任務到達就從線程池中取出一個空閒線程處理,若是全部的線程都處於工做狀態,就添加到隊列,進行排隊。若是隊列中的任務個數大於隊列的所能容納的最大數量,那就不能添加任務到隊列中,只能等待隊列不滿才能添加任務到隊列中多線程
主要由兩個文件組成一個threadpool.h頭文件和一個threadpool.c源文件組成。函數
threadpool.h文件:測試
struct job { void* (*callback_function)(void *arg); //線程回調函數 void *arg; //回調函數參數 struct job *next; }; struct threadpool { int thread_num; //線程池中開啓線程的個數 int queue_max_num; //隊列中最大job的個數 struct job *head; //指向job的頭指針 struct job *tail; //指向job的尾指針 pthread_t *pthreads; //線程池中全部線程的pthread_t pthread_mutex_t mutex; //互斥信號量 pthread_cond_t queue_empty; //隊列爲空的條件變量 pthread_cond_t queue_not_empty; //隊列不爲空的條件變量 pthread_cond_t queue_not_full; //隊列不爲滿的條件變量 int queue_cur_num; //隊列當前的job個數 int queue_close; //隊列是否已經關閉 int pool_close; //線程池是否已經關閉 }; //================================================================================================ //函數名: threadpool_init //函數描述: 初始化線程池 //輸入: [in] thread_num 線程池開啓的線程個數 // [in] queue_max_num 隊列的最大job個數 //輸出: 無 //返回: 成功:線程池地址 失敗:NULL //================================================================================================ struct threadpool* threadpool_init(int thread_num, int queue_max_num); //================================================================================================ //函數名: threadpool_add_job //函數描述: 向線程池中添加任務 //輸入: [in] pool 線程池地址 // [in] callback_function 回調函數 // [in] arg 回調函數參數 //輸出: 無 //返回: 成功:0 失敗:-1 //================================================================================================ int threadpool_add_job(struct threadpool *pool, void* (*callback_function)(void *arg), void *arg); //================================================================================================ //函數名: threadpool_destroy //函數描述: 銷燬線程池 //輸入: [in] pool 線程池地址 //輸出: 無 //返回: 成功:0 失敗:-1 //================================================================================================ int threadpool_destroy(struct threadpool *pool); //================================================================================================ //函數名: threadpool_function //函數描述: 線程池中線程函數 //輸入: [in] arg 線程池地址 //輸出: 無 //返回: 無 //================================================================================================ void* threadpool_function(void* arg);
threadpool.c文件:spa
#include "threadpool.h" struct threadpool* threadpool_init(int thread_num, int queue_max_num) { struct threadpool *pool = NULL; do { pool = malloc(sizeof(struct threadpool)); if (NULL == pool) { printf("failed to malloc threadpool!\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("failed to init mutex!\n"); break; } if (pthread_cond_init(&(pool->queue_empty), NULL)) { printf("failed to init queue_empty!\n"); break; } if (pthread_cond_init(&(pool->queue_not_empty), NULL)) { printf("failed to init queue_not_empty!\n"); break; } if (pthread_cond_init(&(pool->queue_not_full), NULL)) { printf("failed to init queue_not_full!\n"); break; } pool->pthreads = malloc(sizeof(pthread_t) * thread_num); if (NULL == pool->pthreads) { printf("failed to malloc pthreads!\n"); break; } pool->queue_close = 0; pool->pool_close = 0; int i; for (i = 0; i < pool->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)); //隊列滿的時候就等待 } if (pool->queue_close || pool->pool_close) //隊列關閉或者線程池關閉就退出 { pthread_mutex_unlock(&(pool->mutex)); return -1; } struct job *pjob =(struct job*) malloc(sizeof(struct job)); if (NULL == 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)); //隊列空的時候,有任務來時就通知線程池中的線程:隊列非空 } 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) //死循環 { pthread_mutex_lock(&(pool->mutex)); while ((pool->queue_cur_num == 0) && !pool->pool_close) //隊列爲空時,就等待隊列非空 { pthread_cond_wait(&(pool->queue_not_empty), &(pool->mutex)); } if (pool->pool_close) //線程池關閉,線程就退出 { 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)); //隊列爲空,就能夠通知threadpool_destroy函數,銷燬線程函數 } if (pool->queue_cur_num == pool->queue_max_num - 1) { pthread_cond_broadcast(&(pool->queue_not_full)); //隊列非滿,就能夠通知threadpool_add_job函數,添加新任務 } pthread_mutex_unlock(&(pool->mutex)); (*(pjob->callback_function))(pjob->arg); //線程真正要作的工做,回調函數的調用 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) //線程池已經退出了,就直接返回 { pthread_mutex_unlock(&(pool->mutex)); return -1; } pool->queue_close = 1; //置隊列關閉標誌 while (pool->queue_cur_num != 0) { pthread_cond_wait(&(pool->queue_empty), &(pool->mutex)); //等待隊列爲空 } pool->pool_close = 1; //置線程池關閉標誌 pthread_mutex_unlock(&(pool->mutex)); pthread_cond_broadcast(&(pool->queue_not_empty)); //喚醒線程池中正在阻塞的線程 pthread_cond_broadcast(&(pool->queue_not_full)); //喚醒添加任務的threadpool_add_job函數 int i; for (i = 0; i < pool->thread_num; ++i) { pthread_join(pool->pthreads[i], NULL); //等待線程池的全部線程執行完畢 } pthread_mutex_destroy(&(pool->mutex)); //清理資源 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; }
測試文件main.c文件:線程
#include "threadpool.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; }
用gcc編譯,運行就能夠看到效果,1到40個回調函數分別被執行。指針