我尝试了各种改编的或者官方的代码，居然都是错的，最终我发现了问题在于这一行代码

sub_process[pid] = user_count;

就是这行代码把pid赋予数组，但是这个数组有多大呢，代码如下

sub_process = new int[PROCESS_LIMIT ];

会发现代码最大才65536显然比pid号码要小，所以*10就行了改为如下代码

sub_process = new int[PROCESS_LIMIT * 10];

我修改后官方代码清单13-4代码如下，我测试过，是可以运行的，也不会报错了。

#include <arpa/inet.h>
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <netinet/in.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/epoll.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <unistd.h>#define USER_LIMIT 5
#define BUFFER_SIZE 1024
#define FD_LIMIT 65535
#define MAX_EVENT_NUMBER 1024
#define PROCESS_LIMIT 65536struct client_data
{sockaddr_in address;int connfd;pid_t pid;int pipefd[2];
};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;
int *sub_process = 0;
int user_count = 0;
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)
{stop_child = true;
}int run_child(int idx, client_data *users, char *share_mem)
{epoll_event events[MAX_EVENT_NUMBER];int child_epollfd = epoll_create(5);assert(child_epollfd != -1);int connfd = users[idx].connfd;addfd(child_epollfd, connfd);int pipefd = users[idx].pipefd[1];addfd(child_epollfd, pipefd);int ret;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;if ((sockfd == connfd) && (events[i].events & EPOLLIN)){memset(share_mem + idx * BUFFER_SIZE, '\0', BUFFER_SIZE);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{send(pipefd, (char *) &idx, sizeof(idx), 0);}}else if ((sockfd == pipefd) && (events[i].events & EPOLLIN)){int client = 0;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);}}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 * 10];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;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;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;}users[user_count].address = client_address;users[user_count].connfd = connfd;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){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{close(connfd);close(users[user_count].pipefd[1]);addfd(epollfd, users[user_count].pipefd[0]);users[user_count].pid = pid;sub_process[pid] = user_count;user_count++;}}else if ((sockfd == sig_pipefd[0]) && (events[i].events & EPOLLIN)){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:{pid_t pid;int stat;while ((pid = waitpid(-1, &stat, WNOHANG)) > 0){int del_user = sub_process[pid];sub_process[pid] = -1;if ((del_user < 0) || (del_user > USER_LIMIT)){printf("the deleted user was not change\n");continue;}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;printf("child %d exit, now we have %d users\n", del_user, user_count);}if (terminate && user_count == 0){stop_server = true;}break;}case SIGTERM:case SIGINT:{printf("kill all the clild now\n");//addsig( SIGTERM, SIG_IGN );//addsig( SIGINT, SIG_IGN );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){int child = 0;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{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;
}