多线程并发服务器

在使用线程模型开发服务器时需考虑以下问题：

1. 调整进程内最大文件描述符上限
2. 线程如有共享数据，考虑线程同步
3. 服务于客户端线程退出时，退出处理。（退出值，分离态）
4. 系统负载，随着链接客户端增加，导致其它线程不能及时得到CPU

server.c
#include <arpa/inet.h>
#include <netinet/in.h>
#include <pthread.h>
#include <stdio.h>
#include <string.h>

#include "wrap.h"
#define MAXLINE 80
#define SERV_PORT 6666

struct s_info {
    struct sockaddr_in cliaddr;
    int connfd;
};
void *do_work(void *arg) {
    int n, i;
    struct s_info *ts = (struct s_info *) arg;
    char buf[MAXLINE];
    char str[INET_ADDRSTRLEN];
    /* 可以在创建线程前设置线程创建属性,设为分离态,哪种效率高呢？ */
    pthread_detach(pthread_self());
    while (1) {
        n = Read(ts->connfd, buf, MAXLINE);
        if (n == 0) {
            printf("the other side has been closed.\n");
            break;
        }
        printf("received from %s at PORT %d\n",
               inet_ntop(AF_INET, &(*ts).cliaddr.sin_addr, str, sizeof(str)),
               ntohs((*ts).cliaddr.sin_port));
        for (i = 0; i < n; i++)
            buf[i] = toupper(buf[i]);
        Write(ts->connfd, buf, n);
    }
    Close(ts->connfd);
}

int main(void) {
    struct sockaddr_in servaddr, cliaddr;
    socklen_t cliaddr_len;
    int listenfd, connfd;
    int i = 0;
    pthread_t tid;
    struct s_info ts[256];

    listenfd = Socket(AF_INET, SOCK_STREAM, 0);

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(SERV_PORT);

    Bind(listenfd, (struct sockaddr *) &servaddr, sizeof(servaddr));
    Listen(listenfd, 20);

    printf("Accepting connections ...\n");
    while (1) {
        cliaddr_len = sizeof(cliaddr);
        connfd = Accept(listenfd, (struct sockaddr *) &cliaddr, &cliaddr_len);
        ts[i].cliaddr = cliaddr;
        ts[i].connfd = connfd;
        /* 达到线程最大数时，pthread_create出错处理, 增加服务器稳定性 */
        pthread_create(&tid, NULL, do_work, (void *) &ts[i]);
        i++;
    }
    return 0;
}

client.c
#include "wrap.h"
#include <netinet/in.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#define MAXLINE 80
#define SERV_PORT 6666

int main(int argc, char *argv[]) {
    struct sockaddr_in servaddr;
    char buf[MAXLINE];
    int sockfd, n;

    sockfd = Socket(AF_INET, SOCK_STREAM, 0);

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    inet_pton(AF_INET, "127.0.0.1", &servaddr.sin_addr);
    servaddr.sin_port = htons(SERV_PORT);

    Connect(sockfd, (struct sockaddr *) &servaddr, sizeof(servaddr));

    while (fgets(buf, MAXLINE, stdin) != NULL) {
        Write(sockfd, buf, strlen(buf));
        n = Read(sockfd, buf, MAXLINE);
        if (n == 0)
            printf("the other side has been closed.\n");
        else
            Write(STDOUT_FILENO, buf, n);
    }
    Close(sockfd);
    return 0;
}