linux c线程池的原理讲解和代码实现（自行伸缩扩展线程数）

什么是线程池？为什么要使用线程池？

阶段一、一个医院，每天面对成千上万的病人，处理方式是：来一个病人找来一个医生处理，处理完了医生也走了。当看病时间较短的时候，医生来去的时间，显得尤为费时了。

阶段二、医院引进了线程池的概念。设置门诊，把医生全派出去坐诊，病人来看病先挂号排队，医生根据病人队列顺序依次处理各个病人，这样就省去医生来来去去的时间了。但是，很多时候病人不多，医生却很多导致很多医生空闲浪费水电资源撒。

阶段三、医院引进了可伸缩性线程池的概念，如阶段二，但是门诊一开始只派出了部分医生，但是增加了一个领导，病人依旧是排队看病，领导负责协调整个医院的医生。当病人很多医生忙不过来的时候，领导就去多叫几个医生来帮忙；当病人不多医生太多的时候，领导就叫一些医生回家休息去免得浪费医院资源。

阶段三就是一个线程池的例子。

线程池包括：n个执行任务的线程，一个任务队列，一个管理线程

1、预先启动一些线程，线程负责执行任务队列中的任务，当队列空时，线程挂起。

2、调用的时候，直接往任务队列添加任务，并发信号通知线程队列非空。

3、管理线程负责监控任务队列和系统中的线程状态，当任务队列为空，线程数目多且很多处于空闲的时候，便通知一些线程退出以节约系统资源；当任务队列排队任务多且线程都在忙，便负责再多启动一些线程来执行任务，以确保任务执行效率。

代码：如下

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#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 // 领导定时检查队列、线程状态的时间间隔 #define MIN_WAIT_TASK_NUM 10 // 队列中等待的任务数>这个值，便会增加线程 #define DEFAULT_THREAD_VARY 10 //每次线程加减的数目 typedef struct { void *(*function)(void *); void *arg; } threadpool_task_t; struct threadpool_t { pthread_mutex_t lock;// mutex for the taskpool pthread_mutex_t thread_counter;//mutex for count the busy thread pthread_cond_t queue_not_full; pthread_cond_t queue_not_empty;//任务队列非空的信号 pthread_t *threads;//执行任务的线程 pthread_t adjust_tid;//负责管理线程数目的线程 threadpool_task_t *task_queue;//任务队列 int min_thr_num; int max_thr_num; int live_thr_num; int busy_thr_num; int wait_exit_thr_num; int queue_front; int queue_rear; int queue_size; int queue_max_size; bool shutdown; }; /**  * @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  */ bool is_thread_alive(pthread_t tid); int threadpool_free(threadpool_t *pool); //创建线程池 threadpool_t *threadpool_create(int min_thr_num, int max_thr_num, int queue_max_size) { threadpool_t *pool = NULL;  do{  if((pool = (threadpool_t *)malloc(sizeof(threadpool_t))) == NULL)  {  printf("malloc threadpool fail");  break;  }  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;  }  /**  * start work thread min_thr_num  */  for (int i = 0; i < min_thr_num; i++)  { //启动任务线程 pthread_create(&(pool->threads[i]), NULL, threadpool_thread, (void *)pool); printf("start thread 0x%x... ", pool->threads[i]);  } //启动管理线程  pthread_create(&(pool->adjust_tid), NULL, adjust_thread, (void *)pool);  return pool;  }while(0);  threadpool_free(pool); return NULL; } //把任务添加到队列中 int threadpool_add(threadpool_t *pool, void*(*function)(void *arg), void *arg) { assert(pool != NULL); assert(function != NULL); assert(arg != NULL); pthread_mutex_lock(&(pool->lock)); //队列满的时候，等待 while ((pool->queue_size == pool->queue_max_size) && (!pool->shutdown)) { //queue full wait pthread_cond_wait(&(pool->queue_not_full), &(pool->lock)); } if (pool->shutdown) { pthread_mutex_unlock(&(pool->lock)); } //如下是添加任务到队列，使用循环队列 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++; //每次加完任务，发个信号给线程 //若没有线程处于等待状态，此句则无效，但不影响 pthread_cond_signal(&(pool->queue_not_empty)); pthread_mutex_unlock(&(pool->lock)); return 0; } //线程执行任务 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 */ pthread_mutex_lock(&(pool->lock)); //任务队列为空的时候，等待 while ((pool->queue_size == 0) && (!pool->shutdown)) { printf("thread 0x%x is waiting ", pthread_self()); pthread_cond_wait(&(pool->queue_not_empty), &(pool->lock)); //被唤醒后，判断是否是要退出的线程 if (pool->wait_exit_thr_num > 0) { pool->wait_exit_thr_num--; if (pool->live_thr_num > pool->min_thr_num) { printf("thread 0x%x is exiting ", pthread_self());  pool->live_thr_num--;  pthread_mutex_unlock(&(pool->lock));  pthread_exit(NULL); } } } if (pool->shutdown) { pthread_mutex_unlock(&(pool->lock)); printf("thread 0x%x is exiting ", pthread_self()); pthread_exit(NULL); } //get a task from queue 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--; //now queue must be not full pthread_cond_broadcast(&(pool->queue_not_full)); pthread_mutex_unlock(&(pool->lock)); // Get to work printf("thread 0x%x start working ", pthread_self()); pthread_mutex_lock(&(pool->thread_counter)); pool->busy_thr_num++; pthread_mutex_unlock(&(pool->thread_counter)); (*(task.function))(task.arg); // task run over printf("thread 0x%x end working ", pthread_self()); pthread_mutex_lock(&(pool->thread_counter)); pool->busy_thr_num--; pthread_mutex_unlock(&(pool->thread_counter)); } pthread_exit(NULL); return (NULL); } //管理线程 void *adjust_thread(void *threadpool) { threadpool_t *pool = (threadpool_t *)threadpool; while (!pool->shutdown) { sleep(DEFAULT_TIME); 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)); //任务多线程少，增加线程 if (queue_size >= MIN_WAIT_TASK_NUM && live_thr_num < pool->max_thr_num) { //need add thread pthread_mutex_lock(&(pool->lock)); int add = 0; for (int 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)); } //任务少线程多，减少线程 if ((busy_thr_num * 2) < live_thr_num && live_thr_num > pool->min_thr_num) { //need del thread pthread_mutex_lock(&(pool->lock)); pool->wait_exit_thr_num = DEFAULT_THREAD_VARY; pthread_mutex_unlock(&(pool->lock)); //wake up thread to exit for (int i = 0; i < DEFAULT_THREAD_VARY; i++) { pthread_cond_signal(&(pool->queue_not_empty)); } } } } int threadpool_destroy(threadpool_t *pool) { if (pool == NULL) { return -1; } pool->shutdown = true; //adjust_tid exit first pthread_join(pool->adjust_tid, NULL); // wake up the waiting thread pthread_cond_broadcast(&(pool->queue_not_empty)); for (int i = 0; i < pool->min_thr_num; i++) { 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; } bool is_thread_alive(pthread_t tid) { int kill_rc = pthread_kill(tid, 0); if (kill_rc == ESRCH) { return false; } return true; } // for test //void *process(void *arg) //{ //printf("thread 0x%x working on task %d ",pthread_self(),*(int *)arg); //sleep(1); //printf("task %d is end ",*(int *)arg); //return NULL; //} //int main() //{ //threadpool_t *thp = threadpool_create(3,100,12); //printf("pool inited"); // //int *num = (int *)malloc(sizeof(int)*20); //for (int i=0;i<10;i++) //{ //num[i]=i; //printf("add task %d ",i); //threadpool_add(thp,process,(void*)&num[i]); //} //sleep(10); //threadpool_destroy(thp); //}