多线程并发服务器端的实现

实现一个多线程的并发服务器端：

chat_server.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define BUF_SIZE 100
#define MAX_CLNT 256

void* handle_clnt(void* arg);
void send_msg(char* msg, int len);
void error_handling(char* msg);

int clnt_cnt = 0;
int clnt_sockets[MAX_CLNT];
pthread_mutex_t mutx;

int main(int argc, char* argv[])
{
   int serv_sock, clnt_sock;
   struct sockaddr_in serv_adr, clnt_adr;
   socklen_t clnt_adr_size;
   pthread_t t_id;
   if(argc != 2)
   {
        printf("Usage: %s <port>\n", argv[0]);
        exit(1);
   }

   pthread_mutex_init(&mutx, NULL);
   serv_sock = socket(AF_INET, SOCK_STREAM, 0);

   memset(&serv_adr, 0 ,sizeof(serv_adr));
   serv_adr.sin_family = AF_INET;
   serv_adr.sin_addr.s_addr = htonl(INADDR_ANY);
   serv_adr.sin_port = htons(atoi(argv[1]));

   if(bind(serv_sock, (struct sockaddr*)&serv_adr, sizeof(serv_adr)) == -1)
        error_handling("bind() error");
   if(listen(serv_sock, 5) == -1)
        error_handling("listen() error");

    while(1)
    {
        printf("in main thread,pthread_id=%ld\n",pthread_self());
        clnt_adr_size = sizeof(clnt_adr);
        clnt_sock = accept(serv_sock, (struct sockaddr*)&clnt_adr, &clnt_adr_size);

        pthread_mutex_lock(&mutx);
        clnt_sockets[clnt_cnt++] = clnt_sock;
        pthread_mutex_unlock(&mutx);
        printf("clnt_cnt=%d\n",clnt_cnt);
        pthread_create(&t_id, NULL, handle_clnt, (void*)&clnt_sock);
        pthread_detach(t_id);

        printf("Connected client IP:%s\n", inet_ntoa(clnt_adr.sin_addr));

    }

    close(serv_sock);
    return 0;

}

void* handle_clnt(void* arg)
{
    int clnt_sock = *((int*)arg);
    int str_len = 0, i;
    char msg[BUFSIZ];
    while((str_len = read(clnt_sock, msg, sizeof(msg))) != 0)
    {
        send_msg(msg, str_len);
    }


    pthread_mutex_lock(&mutx);
    for(i = 0; i < clnt_cnt; i++)
    {
        if(clnt_sock == clnt_sockets[i])
        {
            while(i++ < clnt_cnt -1)
                clnt_sockets[i] = clnt_sockets[i+1];

            break;
        }
    }

    clnt_cnt--;
    pthread_mutex_unlock(&mutx);
    close(clnt_sock);
    return NULL;
}

void send_msg(char* msg, int len)
{
    int i;
    pthread_mutex_lock(&mutx);
    for(i = 0;i < clnt_cnt; i++)
        write(clnt_sockets[i], msg, len);
    pthread_mutex_unlock(&mutx);

}

void error_handling(char* msg)
{
    fputs(msg, stderr);
    fputc('\n', stderr);
    exit(1);
}

chat_client.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <semaphore.h>
#define BUF_SIZE 100
#define NAME_SIZE 20

void* send_msg(void* arg);
void* recv_msg(void* arg);
void error_handling(char* msg);

char name[NAME_SIZE] = "[default]";
char msg[BUF_SIZE];

int main(int argc, char* argv[])
{
   int sock;
   struct sockaddr_in serv_addr;
   pthread_t snd_thread, rcv_thread;
   void* thread_return;

   if(argc != 4)
   {
        printf("Usage: %s <IP><port><name>\n", argv[0]);
        exit(1);
   }
   sprintf(name, "[%s]", argv[3]);
   sock = socket(AF_INET, SOCK_STREAM, 0);

   memset(&serv_addr, 0 ,sizeof(serv_addr));
   serv_addr.sin_family = AF_INET;
   serv_addr.sin_addr.s_addr = inet_addr(argv[1]);
   serv_addr.sin_port = htons(atoi(argv[2]));

    if(connect(sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) == -1)
    {
        error_handling("connect error");

    }

    pthread_create(&snd_thread, NULL, send_msg, (void*)&sock);
    pthread_create(&rcv_thread, NULL, recv_msg, (void*)&sock);

    printf("snd_thread=%ld,rcv_thread=%ld\n",snd_thread,rcv_thread);

    pthread_join(snd_thread, &thread_return);
    pthread_join(rcv_thread, &thread_return);

    close(sock);
    return 0;
}

void* send_msg(void* arg)
{
    int sock = *((int*)arg);
    char name_msg[NAME_SIZE+BUF_SIZE];
    while(1)
    {
        fgets(msg, BUF_SIZE, stdin);
        if(!strcmp(msg, "q\n") || !strcmp(msg, "Q\n"))
        {
            close(sock);
            exit(0);
        }
        sprintf(name_msg, "%s %s",name,msg);
        write(sock, name_msg, strlen(name_msg));
    }
    return NULL;
}
void* recv_msg(void* arg)
{
    int sock = *((int*)arg);
    char name_msg[NAME_SIZE+BUF_SIZE];
    int str_len;
    while(1)
    {
        str_len = read(sock, name_msg, NAME_SIZE+BUF_SIZE);
        if(str_len == -1)
        {
            return (void*)-1;
        }
        name_msg[str_len] = 0;
        fputs(name_msg, stdout);
    }
    return NULL;
}


void error_handling(char* msg)
{
    fputs(msg, stderr);
    fputc('\n', stderr);
    exit(1);
}

运行结果：chat_server.c

mary@mary-virtual-machine:~/Desktop/Code/tcpserver/pthread$ gcc server.c -o server -lpthread
mary@mary-virtual-machine:~/Desktop/Code/tcpserver/pthread$ ./server 9001
in main thread,pthread_id=139787036530432
clnt_cnt=1
Connected client IP:127.0.0.1
in main thread,pthread_id=139787036530432
clnt_cnt=2
Connected client IP:127.0.0.1
in main thread,pthread_id=139787036530432

运行结果：chat_client.c  One[from yoon]

mary@mary-virtual-machine:~/Desktop/Code/tcpserver/pthread$ gcc client.c -o client -lpthread
mary@mary-virtual-machine:~/Desktop/Code/tcpserver/pthread$ ./client 127.0.0.1 9001 Yoon
snd_thread=139623282448128,rcv_thread=139623274055424
hi,everyone~
[Yoon] hi,everyone~
[Tom] hi yoon

运行结果：chat_client.c Two[from tom]

mary@mary-virtual-machine:~/Desktop/Code/tcpserver/pthread$ ./client 127.0.0.1 9001 Tom
snd_thread=140617132107520,rcv_thread=140617123714816
[Yoon] hi,everyone~
hi yoon
[Tom] hi yoon
 

示例中，需要注意的是临界区的构成方式。

上述示例中的临界区具有如下特点：

“访问全局变量clnt_cnt和数组clnt_socks”的代码将构成临界区”

添加或者删除客户端时，变量clnt_cnt和数组clnt_socks同时发生变化。

因此，在如下的情形中均会导致数据不一致，从而引发严重错误。

 

1. 线程A从数组clnt_socks中删除套接字信息，同时线程B读取clnt_cnt变量
2. 线程A读取变量clnt_cnt,同时线程B将套接字信息添加到clnt_socks数组