线程池实现原理及案列

一、原理图

我们都知道，线程池和多线程的区别就是一个是业务来了动态地去产生线程，一个是把线程事先产生出来放到一个池子中，当要使用线程的时候，从池子中拿出来，当用完后，再把线程放回池子中，但它远远没有这么简单。首先看看原理图，当客户端请求连接时，服务器监听到之后会将其放入到任务队列中，线程再从任务队列中拿走任务，这是两个典型的生产者消费者模型。对于后面的线程池来说，一开始初始化的时候，根据设计的不同，回去限定线程的最大个数，最小个数，初始化多少个等等。

例如：

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*/

监控线程的任务也是简单明了，一般情况就是根据一定的算法去动态的产生于销毁线程。

例如：

GetAllNum表示获取线程池所有的线程数，m_iInitNum 表示初始化的线程数量，iAvailNum 工作的线程数，m_iMaxNum最大线程数，m_iAvailHigh工作线程的最高数量
 if(iAvailNum < m_iAvailLow)
  {
    if(GetAllNum() + m_iInitNum - iAvailNum < m_iMaxNum)
    {
        CreateIdleThread(m_iInitNum - iAvailNum);
    }
    else
    {
      CreateIdleThread(m_iMaxNum - GetAllNum());
    }
  }
  else if(iAvailNum > m_iAvailHigh)
  {
      DeleteIdleThread(1);
  }

或

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));
        }
    }
}
  return NULL;
 }

完整线程池代码

#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                 
#define MIN_WAIT_TASK_NUM 10          
#define DEFAULT_THREAD_VARY 10         
#define true 1
#define false 0

typedef struct {
    void *(*function)(void *);        
    void *arg;                        
} threadpool_task_t;                   

struct threadpool_t {
    pthread_mutex_t lock;              
    pthread_mutex_t thread_counter;     
    pthread_cond_t queue_not_full;     
    pthread_cond_t queue_not_empty;     
    pthread_t *threads;                 
    pthread_t adjust_tid;             
    threadpool_task_t *task_queue;     
    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;                
    int shutdown;                     
};

void *threadpool_thread(void *threadpool);
void *adjust_thread(void *threadpool);
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;        
        }

        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(pthread_t)*max_thr_num);

        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;
        }

        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);    
    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));
    }

    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++;

    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) {
        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));
            if (pool->wait_exit_thr_num > 0) {
            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);
                }
            }
        }

        if (pool->shutdown) {
            pthread_mutex_unlock(&(pool->lock));
            printf("thread 0x%x is exiting\n", (unsigned int)pthread_self());
            pthread_exit(NULL);
        }

        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--;

        pthread_cond_broadcast(&(pool->queue_not_full));

        pthread_mutex_unlock(&(pool->lock));


        printf("thread 0x%x start working\n", (unsigned int)pthread_self());
        pthread_mutex_lock(&(pool->thread_counter));
        pool->busy_thr_num++;                                       
        pthread_mutex_unlock(&(pool->thread_counter));
        (*(task.function))(task.arg);                               
        //task.function(task.arg);                               
        printf("thread 0x%x end working\n", (unsigned int)pthread_self());
        pthread_mutex_lock(&(pool->thread_counter));
        pool->busy_thr_num--;                                       
        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);                                   
        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));
        if (queue_size >= MIN_WAIT_TASK_NUM && live_thr_num < pool->max_thr_num) {
            pthread_mutex_lock(&(pool->lock));
            int add = 0;
            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));
        }

        if ((busy_thr_num * 2) < live_thr_num && live_thr_num > pool->min_thr_num) {

            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++) {

                pthread_cond_signal(&(pool->queue_not_empty));
            }
        }
    }

    return NULL;
}

int threadpool_destroy(threadpool_t *pool)
{
    int i;
    if (pool == NULL) {
        return -1;
    }
    pool->shutdown = true;

    pthread_join(pool->adjust_tid, NULL);

    for (i = 0; i < pool->live_thr_num; i++) {
        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;
}