线程池，简单来说就是有一堆已经创建好的线程（最大数目一定），初始时他们都处于空闲状态，当有新的任务进来，从线程池中取出一个空闲的线程处理任务，然后当任务处理完成之后，该线程被重新放回到线程池中，供其他的任务使用，当线程池中的线程都在处理任务时，就没有空闲线程供使用，此时，若有新的任务产生，只能等待线程池中有线程结束任务空闲才能执行。
首先是用条件变量和互斥量封装的一个状态，用于保护线程池的状态condition.h
#ifndef _CONDITION_H_ #define _CONDITION_H_ #include <pthread.h> //封装一个互斥量和条件变量作为状态 typedef struct condition { pthread_mutex_t pmutex; pthread_cond_t pcond; }condition_t; //对状态的操作函数 int condition_init(condition_t *cond); int condition_lock(condition_t *cond); int condition_unlock(condition_t *cond); int condition_wait(condition_t *cond); int condition_timedwait(condition_t *cond, const struct timespec *abstime); int condition_signal(condition_t* cond); int condition_broadcast(condition_t *cond); int condition_destroy(condition_t *cond); #endif<
condition.c
#include “condition.h” //初始化 int condition_init(condition_t *cond) { int status; if((status = pthread_mutex_init(&cond->pmutex, NULL))) return status; if((status = pthread_cond_init(&cond->pcond, NULL))) return status; return 0; } //加锁 int condition_lock(condition_t *cond) { return pthread_mutex_lock(&cond->pmutex); } //解锁 int condition_unlock(condition_t *cond) { return pthread_mutex_unlock(&cond->pmutex); } //等待 int condition_wait(condition_t *cond) { return pthread_cond_wait(&cond->pcond, &cond->pmutex); } //固定时间等待 int condition_timedwait(condition_t *cond, const struct timespec *abstime) { return pthread_cond_timedwait(&cond->pcond, &cond->pmutex, abstime); } //唤醒一个睡眠线程 int condition_signal(condition_t* cond) { return pthread_cond_signal(&cond->pcond); } //唤醒所有睡眠线程 int condition_broadcast(condition_t *cond) { return pthread_cond_broadcast(&cond->pcond); } //释放 int condition_destroy(condition_t *cond) { int status; if((status = pthread_mutex_destroy(&cond->pmutex))) return status; if((status = pthread_cond_destroy(&cond->pcond))) return status; return 0; }<
然后是线程池对应的threadpool.h和threadpool.c
#ifndef _THREAD_POOL_H_ #define _THREAD_POOL_H_ //线程池头文件 #include “condition.h” //封装线程池中的对象需要执行的任务对象 typedef struct task { void *(*run)(void *args); //函数指针，需要执行的任务 void *arg; //参数 struct task *next; //任务队列中下一个任务 }task_t; //下面是线程池结构体 typedef struct threadpool { condition_t ready; //状态量 task_t *first; //任务队列中第一个任务 task_t *last; //任务队列中最后一个任务 int counter; //线程池中已有线程数 int idle; //线程池中kongxi线程数 int max_threads; //线程池最大线程数 int quit; //是否退出标志 }threadpool_t; //线程池初始化 void threadpool_init(threadpool_t *pool, int threads); //往线程池中加入任务 void threadpool_add_task(threadpool_t *pool, void *(*run)(void *arg), void *arg); //摧毁线程池 void threadpool_destroy(threadpool_t *pool); #endif<
#include “threadpool.h”
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <time.h>
//创建的线程执行
void *thread_routine(void *arg)
{
struct timespec abstime;
int timeout;
printf(“thread %d is starting\n”, (int)pthread_self());
threadpool_t *pool = (threadpool_t *)arg;
while(1)
{
timeout = 0;
//访问线程池之前需要加锁
condition_lock(&pool->ready);
//空闲
pool->idle++;
//等待队列有任务到来 或者 收到线程池销毁通知
while(pool->first == NULL && !pool->quit)
{
//否则线程阻塞等待
printf(“thread %d is waiting\n”, (int)pthread_self());
//获取从当前时间，并加上等待时间， 设置进程的超时睡眠时间
clock_gettime(CLOCK_REALTIME, &abstime);
abstime.tv_sec += 2;
int status;
status = condition_timedwait(&pool->ready, &abstime); //该函数会解锁，允许其他线程访问，当被唤醒时，加锁
if(status == ETIMEDOUT)
{
printf(“thread %d wait timed out\n”, (int)pthread_self());
timeout = 1;
break;
}
}
pool->idle–;
if(pool->first != NULL)
{
//取出等待队列最前的任务，移除任务，并执行任务
task_t *t = pool->first;
pool->first = t->next;
//由于任务执行需要消耗时间，先解锁让其他线程访问线程池
condition_unlock(&pool->ready);
//执行任务
t->run(t->arg);
//执行完任务释放内存
free(t);
//重新加锁
condition_lock(&pool->ready);
}
//退出线程池
if(pool->quit && pool->first == NULL)
{
pool->counter–;//当前工作的线程数-1
//若线程池中没有线程，通知等待线程（主线程）全部任务已经完成
if(pool->counter == 0)
{
condition_signal(&pool->ready);
}
condition_unlock(&pool->ready);
break;
}
//超时，跳出销毁线程
if(timeout == 1)
{
pool->counter–;//当前工作的线程数-1
condition_unlock(&pool->ready);
break;
}
condition_unlock(&pool->ready);
}
printf(“thread %d is exiting\n”, (int)pthread_self());
return NULL;
}
//线程池初始化
void threadpool_init(threadpool_t *pool, int threads)
{
condition_init(&pool->ready);
pool->first = NULL;
pool->last =NULL;
pool->counter =0;
pool->idle =0;
pool->max_threads = threads;
pool->quit =0;
}
//增加一个任务到线程池
void threadpool_add_task(threadpool_t *pool, void *(*run)(void *arg), void *arg)
{
//产生一个新的任务
task_t *newtask = (task_t *)malloc(sizeof(task_t));
newtask->run = run;
newtask->arg = arg;
newtask->next=NULL;//新加的任务放在队列尾端
//线程池的状态被多个线程共享，操作前需要加锁
condition_lock(&pool->ready);
if(pool->first == NULL)//第一个任务加入
{
pool->first = newtask;
}
else
{
pool->last->next = newtask;
}
pool->last = newtask; //队列尾指向新加入的线程
//线程池中有线程空闲，唤醒
if(pool->idle > 0)
{
condition_signal(&pool->ready);
}
//当前线程池中线程个数没有达到设定的最大值，创建一个新的线性
else if(pool->counter < pool->max_threads)
{
pthread_t tid;
pthread_create(&tid, NULL, thread_routine, pool);
pool->counter++;
}
//结束，访问
condition_unlock(&pool->ready);
}
//线程池销毁
void threadpool_destroy(threadpool_t *pool)
{
//如果已经调用销毁，直接返回
if(pool->quit)
{
return;
}
//加锁
condition_lock(&pool->ready);
//设置销毁标记为1
pool->quit = 1;
//线程池中线程个数大于0
if(pool->counter > 0)
{
//对于等待的线程，发送信号唤醒
if(pool->idle > 0)
{
condition_broadcast(&pool->ready);
}
//正在执行任务的线程，等待他们结束任务
while(pool->counter)
{
condition_wait(&pool->ready);
}
}
condition_unlock(&pool->ready);
condition_destroy(&pool->ready);
}<
测试代码：
#include “threadpool.h” #include <unistd.h> #include <stdlib.h> #include <stdio.h> void* mytask(void *arg) { printf(“thread %d is working on task %d\n”, (int)pthread_self(), *(int*)arg); sleep(1); free(arg); return NULL; } //测试代码 int main(void) { threadpool_t pool; //初始化线程池，最多三个线程 threadpool_init(&pool, 3); int i; //创建十个任务 for(i=0; i < 10; i++) { int *arg = malloc(sizeof(int)); *arg = i; threadpool_add_task(&pool, mytask, arg); } threadpool_destroy(&pool); return 0; }<
