谈一谈linux下线程池
什么是线程池：
首先，顾名思义，就是把一堆开辟好的线程放在一个池子里统一管理，就是一个线程池。
其次，为什么要用线程池，难道来一个请求给它申请一个线程，请求处理完了释放线程不行么？也行，但是如果创建线程和销毁线程的时间比线程处理请求的时间长，而且请求很多的情况下，我们的CPU资源都浪费在了创建和销毁线程上了，所以这种方法的效率比较低，于是，我们可以将若干已经创建完成的线程放在一起统一管理，如果来了一个请求，我们从线程池中取出一个线程来处理，处理完了放回池内等待下一个任务，线程池的好处是避免了繁琐的创建和结束线程的时间，有效的利用了CPU资源。
按照我的理解，线程池的作用和双缓冲的作用类似，可以完成任务处理的“鱼贯”动作。
最后，如何才能创建一个线程池的模型呢，一般需要以下三个参与者：
1、线程池结构，它负责管理多个线程并提供任务队列的接口
2、工作线程，它们负责处理任务
3、任务队列，存放待处理的任务
有了三个参与者，下一个问题就是怎么使线程池安全有序的工作，可以使用POSIX中的信号量、互斥锁和条件变量等同步手段。有了这些认识，我们就可以创建自己的线程池
代码示例如下：
#include <stdlib.h> #include <pthread.h> #include <unistd.h> #include <assert.h> #include <stdio.h> #include <string.h> #include <signal.h> #include <errno.h> #include "threadpool.h" #define DEFAULT_TIME 10 /*10s检测一次*/ #define MIN_WAIT_TASK_NUM 10 /*如果queue_size > MIN_WAIT_TASK_NUM 添加新的线程到线程池*/ #define DEFAULT_THREAD_VARY 10 /*每次创建和销毁线程的个数*/ #define true 1 #define false 0 typedef struct { void *(*function)(void *); /*函数指针，回调函数*/ void *arg; /*上面函数的参数*/ } threadpool_task_t; /*任务结构体*/ struct threadpool_t { pthread_mutex_t lock; /*用于锁住当前这个结构体体taskpoll*/ pthread_mutex_t thread_counter; /*记录忙状态线程个数*/ pthread_cond_t queue_not_full; /*当任务队列满时，添加任 务的线程阻塞，等待此条件变量*/ pthread_cond_t queue_not_empty; /*任务队列里不为空时，通知等待任务的线程*/ pthread_t *threads; /*保存工作线程tid的数组*/ pthread_t adjust_tid; /*管理线程tid*/ threadpool_task_t *task_queue; /*任务队列*/ int min_thr_num; /*线程组内默认最小线程数*/ int max_thr_num; /*线程组内默认最大线程数*/ int live_thr_num; /*当前存活线程个数*/ int busy_thr_num; /*忙状态线程个数*/ int wait_exit_thr_num; /*要销毁的线程个数*/ int queue_front; /*队头索引下标*/ int queue_rear; /*队未索引下标*/ int queue_size; /*队中元素个数*/ int queue_max_size; /*队列中最大容纳个数*/ int shutdown; /*线程池使用状态，true或false*/ }; /** * @function void *threadpool_thread(void *threadpool) * @desc the worker thread * @param threadpool the pool which own the thread */ void *threadpool_thread(void *threadpool); /** * @function void *adjust_thread(void *threadpool); * @desc manager thread * @param threadpool the threadpool */ void *adjust_thread(void *threadpool); /** * check a thread is alive */ int is_thread_alive(pthread_t tid); int threadpool_free(threadpool_t *pool); threadpool_t *threadpool_create(int min_thr_num, int max_thr_num, int queue_max_size) { int i; threadpool_t *pool = NULL; do{ if((pool = (threadpool_t *)malloc(sizeof(threadpool_t))) == NULL) { printf("malloc threadpool fail"); break; /*跳出do while*/ } pool->min_thr_num = min_thr_num; pool->max_thr_num = max_thr_num; pool->busy_thr_num = 0; pool->live_thr_num = min_thr_num; pool->queue_size = 0; pool->queue_max_size = queue_max_size; pool->queue_front = 0; pool->queue_rear = 0; pool->shutdown = false; pool->threads = (pthread_t *)malloc(sizeof(pthread_t)*max_thr_num); if (pool->threads == NULL) { printf("malloc threads fail"); break; } memset(pool->threads, 0, sizeof(pool->threads)); pool->task_queue = (threadpool_task_t *)malloc(sizeof(threadpool_task_t)*queue_max_size); if (pool->task_queue == NULL) { printf("malloc task_queue fail"); break; } if (pthread_mutex_init(&(pool->lock), NULL) != 0 || pthread_mutex_init(&(pool->thread_counter), NULL) != 0 || pthread_cond_init(&(pool->queue_not_empty), NULL) != 0 || pthread_cond_init(&(pool->queue_not_full), NULL) != 0) { printf("init the lock or cond fail"); break; } /* 启动min_thr_num个work thread */ for (i = 0; i < min_thr_num; i++) { pthread_create(&(pool->threads[i]), NULL, threadpool_thread, (void *)pool); printf("start thread 0x%x...\n", (unsigned int)pool->threads[i]); } pthread_create(&(pool->adjust_tid), NULL, adjust_thread, (void *)pool); return pool; }while(0); threadpool_free(pool); /*前面代码调用失败时，释放poll存储空间*/ return NULL; } int threadpool_add(threadpool_t *pool, void*(*function)(void *arg), void *arg) { pthread_mutex_lock(&(pool->lock)); while ((pool->queue_size == pool->queue_max_size) && (!pool->shutdown)) { pthread_cond_wait(&(pool->queue_not_full), &(pool->lock)); } if (pool->shutdown) { pthread_mutex_unlock(&(pool->lock)); } /*添加任务到任务队列里*/ if (pool->task_queue[pool->queue_rear].arg != NULL) { free(pool->task_queue[pool->queue_rear].arg); pool->task_queue[pool->queue_rear].arg = NULL; } pool->task_queue[pool->queue_rear].function = function; pool->task_queue[pool->queue_rear].arg = arg; pool->queue_rear = (pool->queue_rear + 1)%pool->queue_max_size; pool->queue_size++; /*任务队列不为空，唤醒等待处理任务的线程*/ pthread_cond_signal(&(pool->queue_not_empty)); pthread_mutex_unlock(&(pool->lock)); return 0; } void *threadpool_thread(void *threadpool) { threadpool_t *pool = (threadpool_t *)threadpool; threadpool_task_t task; while(true) { /* Lock must be taken to wait on conditional variable */ /*刚创建出线程，等待任务队列里有任务，否则阻塞等待任务队列里有任务后再唤醒接收任务*/ pthread_mutex_lock(&(pool->lock)); while ((pool->queue_size == 0) && (!pool->shutdown)) { printf("thread 0x%x is waiting\n", (unsigned int)pthread_self()); pthread_cond_wait(&(pool->queue_not_empty), &(pool->lock)); /*清除指定数目的空闲线程，如果要结束的线程个数大于0，结束线程*/ if (pool->wait_exit_thr_num > 0) { pool->wait_exit_thr_num--; /*如果线程池里线程个数大于最小值时可以结束当前线程*/ if (pool->live_thr_num > pool->min_thr_num) { printf("thread 0x%x is exiting\n", (unsigned int)pthread_self()); pool->live_thr_num--; pthread_mutex_unlock(&(pool->lock)); pthread_exit(NULL); } } } /*如果指定了true，要关闭线程池里的每个线程，自行退出处理*/ if (pool->shutdown) { pthread_mutex_unlock(&(pool->lock)); printf("thread 0x%x is exiting\n", (unsigned int)pthread_self()); pthread_exit(NULL); } /*从任务队列里获得任务*/ task.function = pool->task_queue[pool->queue_front].function; task.arg = pool->task_queue[pool->queue_front].arg; pool->queue_front = (pool->queue_front + 1)%pool->queue_max_size; pool->queue_size--; /*通知可以有新的任务添加进来*/ pthread_cond_broadcast(&(pool->queue_not_full)); pthread_mutex_unlock(&(pool->lock)); /*执行任务*/ printf("thread 0x%x start working\n", (unsigned int)pthread_self()); pthread_mutex_lock(&(pool->thread_counter)); pool->busy_thr_num++; /*忙状态线程数加1*/ pthread_mutex_unlock(&(pool->thread_counter)); (*(task.function))(task.arg); /*执行回调函数任务*/ //task.function(task.arg); /*执行回调函数任务*/ /*任务结束处理*/ printf("thread 0x%x end working\n", (unsigned int)pthread_self()); pthread_mutex_lock(&(pool->thread_counter)); pool->busy_thr_num--; /*忙状态数减1*/ pthread_mutex_unlock(&(pool->thread_counter)); } pthread_exit(NULL); //return (NULL); } void *adjust_thread(void *threadpool) { int i; threadpool_t *pool = (threadpool_t *)threadpool; while (!pool->shutdown) { sleep(DEFAULT_TIME); /*延时10秒*/ pthread_mutex_lock(&(pool->lock)); int queue_size = pool->queue_size; int live_thr_num = pool->live_thr_num; pthread_mutex_unlock(&(pool->lock)); pthread_mutex_lock(&(pool->thread_counter)); int busy_thr_num = pool->busy_thr_num; pthread_mutex_unlock(&(pool->thread_counter)); /*任务数大于最小线程池个数并且存活的线程数少于最大线程个数时，创建新线程*/ if (queue_size >= MIN_WAIT_TASK_NUM && live_thr_num < pool->max_thr_num) { pthread_mutex_lock(&(pool->lock)); int add = 0; /*一次增加DEFAULT_THREAD个线程*/ for (i = 0; i < pool->max_thr_num && add < DEFAULT_THREAD_VARY && pool->live_thr_num < pool->max_thr_num; i++) { if (pool->threads[i] == 0 || !is_thread_alive(pool->threads[i])) { pthread_create(&(pool->threads[i]), NULL, threadpool_thread, (void *)pool); add++; pool->live_thr_num++; } } pthread_mutex_unlock(&(pool->lock)); } /*销毁多余的空闲线程*/ if ((busy_thr_num * 2) < live_thr_num && live_thr_num > pool->min_thr_num) { /*一次销毁DEFAULT_THREAD个线程*/ pthread_mutex_lock(&(pool->lock)); pool->wait_exit_thr_num = DEFAULT_THREAD_VARY; pthread_mutex_unlock(&(pool->lock)); for (i = 0; i < DEFAULT_THREAD_VARY; i++) { /*通知处在空闲状态的线程*/ pthread_cond_signal(&(pool->queue_not_empty)); } } } } int threadpool_destroy(threadpool_t *pool) { int i; if (pool == NULL) { return -1; } pool->shutdown = true; /*先销毁管理线程*/ pthread_join(pool->adjust_tid, NULL); for (i = 0; i < pool->live_thr_num; i++) { /*通知所有的空闲线程*/ pthread_cond_broadcast(&(pool->queue_not_empty)); pthread_join(pool->threads[i], NULL); } threadpool_free(pool); return 0; } int threadpool_free(threadpool_t *pool) { if (pool == NULL) { return -1; } if (pool->task_queue) { free(pool->task_queue); } if (pool->threads) { free(pool->threads); pthread_mutex_lock(&(pool->lock)); pthread_mutex_destroy(&(pool->lock)); pthread_mutex_lock(&(pool->thread_counter)); pthread_mutex_destroy(&(pool->thread_counter)); pthread_cond_destroy(&(pool->queue_not_empty)); pthread_cond_destroy(&(pool->queue_not_full)); } free(pool); pool = NULL; return 0; } int threadpool_all_threadnum(threadpool_t *pool) { int all_threadnum = -1; pthread_mutex_lock(&(pool->lock)); all_threadnum = pool->live_thr_num; pthread_mutex_unlock(&(pool->lock)); return all_threadnum; } int threadpool_busy_threadnum(threadpool_t *pool) { int busy_threadnum = -1; pthread_mutex_lock(&(pool->thread_counter)); busy_threadnum = pool->busy_thr_num; pthread_mutex_unlock(&(pool->thread_counter)); return busy_threadnum; } int is_thread_alive(pthread_t tid) { int kill_rc = pthread_kill(tid, 0); if (kill_rc == ESRCH) { return false; } return true; } /*测试使用，作成库时请注释掉下面代码*/ #if 1 void *process(void *arg) { printf("thread 0x%x working on task %d\n ",(unsigned int)pthread_self(),*(int *)arg); sleep(1); printf("task %d is end\n",*(int *)arg); return NULL; } int main(void) { threadpool_t *thp = threadpool_create(3,100,100); /*线程池里最小3个线程，最大100个，队列最大值12*/ printf("pool inited"); int *num = (int *)malloc(sizeof(int)*20); //int num[20]; int i; for (i=0;i<10;i++) { num[i]=i; printf("add task %d\n",i); threadpool_add(thp,process,(void*)&num[i]); } sleep(10); threadpool_destroy(thp); } #endif
