高并发服务器学习笔记之五：线程池模型

对于多线程模型，假设某一时刻，突然涌入大量的客户端请求，超过了系统创建的上限，如果程序处理的不好很容易把服务器搞挂掉。而且虽然线程的创建比进程的创建开销要小，但还是有一定的开销的。那么，我们能不能想个办法，既能控制住线程的数量使其不要超过系统的上限，又能减少线程创建的开销呢？于是乎就有了线程池的出现。

线程池的想法是，在程序启动后，先创建一定数量的线程，每个线程都不停的看任务队列是否有任务发生，如果有，则领取任务去干活，如果没有就阻塞，直到有任务到来。而主线程就负责往任务队列里丢任务，并且告诉线程池中的所有线程有任务来了。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

#include <pthread.h>
#include <unistd.h>
#include <sys/types.h>          /* See NOTES */
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h> /* superset of previous */
#include <arpa/inet.h>

#include "public_head.h"

#define LISTEN_BACKLOG 50
#define QUEUE_MAX	100
#define THREAD_COUNT	3

static int clientfd[QUEUE_MAX];
static int *client_start;
static int *client_end;

static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;

void handle_request(int acceptfd)
{
	int i = 0; 
    ssize_t readret = 0;
    char read_buff[256] = { 0 };
    char write_buff[256] = { 0 };
   
	while (1)
	{
		memset(read_buff, 0, sizeof(read_buff));
		readret = read(acceptfd, read_buff, sizeof(read_buff));
		if (readret == 0)
			break;

		printf("thread id:%lu, recv message:%s\n", pthread_self(), read_buff);

		memset(write_buff, 0, sizeof(write_buff));
		sprintf(write_buff, "This is server send message:%d", i++);
		write(acceptfd, write_buff, sizeof(write_buff));
	}

    printf("\n");
    close(acceptfd);
    return;
}

void *thread_func(void *arg)
{
	int fd;
	while (1)
	{
		pthread_mutex_lock(&mutex);
		while (client_start >= client_end)
		{
			pthread_cond_wait(&cond, &mutex);
			continue;
		}

		fd = *client_start;
		*client_start = -1;
		client_start++;
		pthread_mutex_unlock(&mutex);
		if(fd > 0)
			handle_request(fd);
	}
}


int main(int argc, char ** argv)
{
	int i = 0;
    int sockfd = 0;
    int acceptfd = 0;
    socklen_t client_addr_len = 0;
    struct sockaddr_in server_addr, client_addr;

    char client_ip[16] = { 0 };

	pthread_t tids[THREAD_COUNT];

	client_start = client_end = clientfd;

    memset(&server_addr, 0, sizeof(server_addr));
    memset(&client_addr, 0, sizeof(client_addr));

    if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
        handle_error("socket");

    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(9527);
    server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    if(bind(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0)
    {
		char buff[256] = { 0 };
        close(sockfd);
		strerror_r(errno, buff, sizeof(buff));
        handle_error("bind");
    }

    if(listen(sockfd, LISTEN_BACKLOG) < 0)
    {
        close(sockfd);
        handle_error("listen");
    }

	for (i = 0; i < QUEUE_MAX; ++i)
	{
		clientfd[i] = -1;
	}

	for (i = 0; i < THREAD_COUNT; ++i)
	{
		if (pthread_create(tids + i, NULL, thread_func, NULL) != 0)
		{
			close(sockfd);
			handle_error("pthread_create");
		}
	}

    while(1)
    {
        client_addr_len = sizeof(client_addr);
        if((acceptfd = accept(sockfd, (struct sockaddr *)&client_addr, &client_addr_len)) < 0)
        {
            perror("accept");
            continue;
        }
       
        memset(client_ip, 0, sizeof(client_ip));
        inet_ntop(AF_INET,&client_addr.sin_addr,client_ip,sizeof(client_ip)); 
        printf("client:%s:%d\n",client_ip,ntohs(client_addr.sin_port));

	//	pthread_mutex_lock(&mutex);
		*client_end = acceptfd;
		client_end++;
	//	pthread_mutex_unlock(&mutex);
		pthread_cond_signal(&cond);
    }
    
    close(sockfd);

    return 0;
}