基于共享内存的聊天室服务程序

服务器代码如下：

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <assert.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/epoll.h>
#include <signal.h>
#include <sys/wait.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>

#define USER_LIMIT 5
#define BUFFER_SIZE 1024
#define FD_LIMIT 65535
#define MAX_EVENT_NUMBER 1024
#define PROCESS_LIMIT 65536

struct client_data {
    sockaddr_in address; // 客户端ip地址
    int connfd;         // socket文件描述符
    pid_t pid;         //  处理这个连接的子进程pid
    int pipefd[2];      // 和父进程通信用的管道
};

static const char* shm_name = "/my_shm";
int sig_pipefd[2];
int epollfd;
int listenfd;
int shmfd;

char* share_mem = 0;

client_data* users = 0; // 客户连接数组，进程用客户连接的编号来索引这个数组

int* sub_process = 0; // 子进程和客户连接的映射关系表。用进程的pid来索引这个数组，即可取得该进程 所处理的客户连接 的编号

int user_count = 0; // 当前客户数量
bool stop_child = false;

int setnonblocking(int fd) {
    int old_option = fcntl(fd, F_GETFL);
    int new_option = old_option | O_NONBLOCK;
    fcntl(fd, F_SETFL, new_option);
    return old_option;
}

void addfd(int epollfd, int fd) {
    epoll_event event;
    event.data.fd = fd;
    event.events = EPOLLIN | EPOLLET;
    epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &event);
    setnonblocking(fd);
}

void sig_handler(int sig) {
    int save_errno = errno;
    int msg = sig;
    send(sig_pipefd[1], (char*)&msg, 1, 0);
    errno = save_errno;
}

void addsig(int sig, void(*handler)(int), bool restart = true) {
    struct sigaction sa;
    memset(&sa, '\0', sizeof(sa));
    sa.sa_handler = handler;
    if (restart) {
        sa.sa_flags |= SA_RESTART;
    }
    sigfillset(&sa.sa_mask);
    assert(sigaction(sig, &sa, NULL) != -1);
}

void del_resource() {
    close(sig_pipefd[0]);
    close(sig_pipefd[1]);
    close(listenfd);
    close(epollfd);
    shm_unlink(shm_name);
    delete[] users;
    delete[] sub_process;
}

void child_term_handler(int sig) { // 停止一个子进程
    stop_child = true;
}

// 子进程运行的函数。参数idx指出该子进程处理的客户连接的编号，users是保存所有客户连接数据的数组。参数share_mem指出共享内存的起始地址
int run_child(int idx, client_data* users, char* share_mem) {
    epoll_event events[MAX_EVENT_NUMBER];
    // 子进程用io复用技术来同时监听两个文件描述符： 客户连接socket和与父进程的管道文件描述符
    int child_epollfd = epoll_create(5);
    assert(child_epollfd != -1);
    int connfd = users[idx].connfd; // 客户端socket
    addfd(child_epollfd, connfd);
    int pipefd = users[idx].pipefd[1]; // 父进程管道文件描述符
    addfd(child_epollfd, pipefd);
    int ret;
    // 子进程设置自己的信号处理函数
    addsig(SIGTERM, child_term_handler, false);

    while (!stop_child) {
        int number = epoll_wait(child_epollfd, events, MAX_EVENT_NUMBER, -1);
        if ((number < 0) && (errno != EINTR)) {
            printf("epoll failure\n");
            break;
        }

        for (int i = 0; i < number; i++) {
            int sockfd = events[i].data.fd;
            // 本子进程负责的客户连接有数据到达
            if ((sockfd == connfd) && (events[i].events & EPOLLIN)) {
                memset(share_mem + idx * BUFFER_SIZE, '\0', BUFFER_SIZE);
                // 将客户数据读取到对应 读缓存 中。 读缓存是共享内存的一段，开始于 idx*BUFFER_SIZE处，长度为BUFFER_SIZE字节。因此，各个客户连接的
                // 读缓存是共享的
                ret = recv(connfd, share_mem + idx * BUFFER_SIZE, BUFFER_SIZE - 1, 0);
                if (ret < 0) {
                    if (errno != EAGAIN) {
                        stop_child = true;
                    }
                } else if (ret == 0) {
                    stop_child = true;
                } else {
                    // 成功读取客户数据后就通知主进程（通过管道）来处理
                    send(pipefd, (char*)&idx, sizeof(idx), 0);
                }
                // 主进程通知本进程（通过管道）将第client个客户的数据发送到本进程负责处理的客户端
            } else if ((sockfd == pipefd) && (events[i].events & EPOLLIN)) {
                int client = 0;
                // 接收主进程发送来的数据，即 有客户数据到达的连接 的编号。
                ret = recv(sockfd, (char*)&client, sizeof(client), 0);
                if (ret < 0) {
                    if (errno != EAGAIN) {
                        stop_child = true;
                    }
                } else if (ret == 0) {
                    stop_child = true;
                } else {
                    send(connfd, share_mem + client * BUFFER_SIZE, BUFFER_SIZE, 0); // 通知这个子进程负责的connfd，有个编号为client的客户端发消息了，把这段消息发给connfd
                }
            } else {
                continue;
            }
        }
    }

    close(connfd);
    close(pipefd);
    close(child_epollfd);
    return 0;
}

int main(int argc, char* argv[])
{
    if (argc <= 2) {
        printf("usage: %s ip_address port_number\n", basename(argv[0]));
        return 1;
    }
    const char* ip = argv[1];
    int port = atoi(argv[2]);

    int ret = 0;
    struct sockaddr_in address;
    bzero(&address, sizeof(address));
    address.sin_family = AF_INET;
    inet_pton(AF_INET, ip, &address.sin_addr);
    address.sin_port = htons(port);

    listenfd = socket(PF_INET, SOCK_STREAM, 0);
    assert(listenfd >= 0);

    ret = bind(listenfd, (struct sockaddr*)&address, sizeof(address));
    assert(ret != -1);

    ret = listen(listenfd, 5);
    assert(ret != -1);

    user_count = 0;
    users = new client_data[USER_LIMIT + 1];
    sub_process = new int[PROCESS_LIMIT];
    for (int i = 0; i < PROCESS_LIMIT; ++i) {
        sub_process[i] = -1;
    }

    epoll_event events[MAX_EVENT_NUMBER];
    epollfd = epoll_create(5);
    assert(epollfd != -1);
    addfd(epollfd, listenfd);

    ret = socketpair(PF_UNIX, SOCK_STREAM, 0, sig_pipefd);
    assert(ret != -1);
    setnonblocking(sig_pipefd[1]);
    addfd(epollfd, sig_pipefd[0]);

    addsig(SIGCHLD, sig_handler);
    addsig(SIGTERM, sig_handler);
    addsig(SIGINT, sig_handler);
    addsig(SIGPIPE, SIG_IGN);
    bool stop_server = false;
    bool terminate = false;

    // 创建共享内存，作为所有客户socket连接的读缓存
    shmfd = shm_open(shm_name, O_CREAT | O_RDWR, 0666);
    assert(shmfd != -1);
    ret = ftruncate(shmfd, USER_LIMIT * BUFFER_SIZE);
    assert(ret != -1);

    share_mem = (char*)mmap(NULL, USER_LIMIT * BUFFER_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, shmfd, 0);
    assert(share_mem != MAP_FAILED);
    close(shmfd);

    while (!stop_server) {
        int number = epoll_wait(epollfd, events, MAX_EVENT_NUMBER, -1);
        if ((number < 0) && (errno != EINTR)) {
            printf("epoll failure\n");
            break;
        }

        for (int i = 0; i < number; i++) {
            int sockfd = events[i].data.fd;
            // 新的客户连接到来
            if (sockfd == listenfd) {
                struct sockaddr_in client_address;
                socklen_t client_addrlength = sizeof(client_address);
                int connfd = accept(listenfd, (struct sockaddr*)&client_address, &client_addrlength);

                if (connfd < 0) {
                    printf("errno is: %d\n", errno);
                    continue;
                }
                if (user_count >= USER_LIMIT) {
                    const char* info = "too many users\n";
                    printf("%s", info);
                    send(connfd, info, strlen(info), 0);
                    close(connfd);
                    continue;
                }

                // 保存第user_counter个客户连接的相关数据
                users[user_count].address = client_address;
                users[user_count].connfd = connfd;
                // 在主进程和子进程间建立管道，以传递必要数据
                ret = socketpair(PF_UNIX, SOCK_STREAM, 0, users[user_count].pipefd);
                assert(ret != -1);
                pid_t pid = fork();
                if (pid < 0) {
                    close(connfd);
                    continue;
                } else if (pid == 0) { // 子进程
                    close(epollfd);
                    close(listenfd);
                    close(users[user_count].pipefd[0]);
                    close(sig_pipefd[0]);
                    close(sig_pipefd[1]);
                    run_child(user_count, users, share_mem);
                    munmap((void*)share_mem, USER_LIMIT * BUFFER_SIZE);
                    exit(0);
                } else { // 父进程
                    close(connfd);
                    close(users[user_count].pipefd[1]);
                    addfd(epollfd, users[user_count].pipefd[0]); // 监听子进程的管道
                    users[user_count].pid = pid;
                    // 记录新的客户连接在数组users中的索引值，建立进程pid和该索引值之间的映射关系
                    sub_process[pid] = user_count;
                    user_count++;
                }
            } else if ((sockfd == sig_pipefd[0]) && events[i].events & EPOLLIN) { // 处理信号事件
                int sig;
                char signals[1024];
                ret = recv(sig_pipefd[0], signals, sizeof(signals), 0);
                if (ret == -1) {
                    continue;
                } else if (ret == 0) {
                    continue;
                } else {
                    for (int i = 0; i < ret; ++i) {
                        switch(signals[i]) {
                            case SIGCHLD: { // 子进程推出，表示有某个客户端关闭了连接
                                pid_t pid;
                                int stat;
                                while ((pid = waitpid(-1, &stat, WNOHANG)) > 0) {
                                    // 用子进程的pid取得被关闭的客户连接的编号
                                    int del_user = sub_process[pid];
                                    sub_process[pid] = -1;
                                    if ((del_user < 0) || (del_user > USER_LIMIT)) {
                                        continue;
                                    }
                                    // 清除第del_user个客户连接使用的相关数据
                                    epoll_ctl(epollfd, EPOLL_CTL_DEL, users[del_user].pipefd[0], 0);
                                    close(users[del_user].pipefd[0]);
                                    users[del_user] = users[--user_count];
                                    sub_process[users[del_user].pid] = del_user;
                                }
                                if (terminate && user_count == 0) {
                                    stop_server = true;
                                }
                                break;
                            }
                            case SIGTERM:
                            case SIGINT: { // 结束服务器程序
                                printf("kill all the child now\n");
                                if (user_count == 0) {
                                    stop_server = true;
                                    break;
                                }
                                for (int i = 0; i < user_count; ++i) {
                                    int pid = users[i].pid;
                                    kill(pid, SIGTERM);
                                }
                                terminate = true;
                                break;
                            }
                            default: {
                                break;
                            }
                        }
                    }
                }
            } else if (events[i].events & EPOLLIN) { // 某个子进程向父进程写入了数据
                int child = 0;
                // 读取管道数据，child变量记录了是哪个客户连接有数据到达
                ret = recv(sockfd, (char*)&child, sizeof(child), 0);
                printf("read data from child accross pipe\n");
                if (ret == -1) {
                    continue;
                } else if (ret == 0) {
                    continue;
                } else {
                    // 向除负责处理第child个客户连接的子进程之外的其他子进程发送消息，通知他们有客户数据要写
                    for (int j = 0; j < user_count; ++j) {
                        if (users[j].pipefd[0] != sockfd) {
                            printf("send data to child accross pipe\n");
                            send(users[j].pipefd[0], (char*)&child, sizeof(child), 0);
                        }
                    }
                }
            }
        }
    }
    del_resource();
    return 0;
}

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server:

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client 1:

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client 2:

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先让服务器监听4444端口，之后客户端1连接，客户端2连接。客户端1发送11111，发现客户端1和2都能收到。客户端2发送2222，发现客户端1和2都能收到。

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reference: linux高性能服务器编程——游双$P_{255}$