UNIX网络编程5.8POSIX信号处理5.9处理SIGCHLD信号

信号signal就是告知某个进程发生了某个事件的通知，有时也称为软件中断（software interrupt)，信号通常是异步发生的，也就是说，进程预先不知道信号的准确发生时间。

信号可以：

由一个进程发给另一个进程（或者自身）。

由内核发给某进程。

/* include signal */
#include "unpsunyj.h"

Sigfunc* signal(int signo, Sigfunc *func)
{
    struct sigaction act, oact;

    act.sa_handler = func;
    sigemptyset(&act.sa_mask);
    act.sa_flags = 0;
    if (signo == SIGALRM) {
#ifdef SA_INTERRUPT
        act.sa_flags |= SA_INTERRUPT; /* SunOS 4.x */
#endif
    } else {
#ifdef SA_RESTART
        act.sa_flags |= SA_RESTART; /* SVR4, 44BSD */
#endif
    }
    if (sigaction(signo, &act, &oact) < 0)
        return(SIG_ERR);
    return(oact.sa_handler);
}
/* end signal */

Sigfunc* Signal(int signo, Sigfunc *func) /* for our signal() function */
{
    Sigfunc* sigfunc;

    if ( (sigfunc = signal(signo, func)) == SIG_ERR)
        err_sys("signal error");
    return(sigfunc);
}

#include <iostream>
#include "../lib/unpsunyj.h"

int main(int argc, char** argv)
{
    int                listenfd;
    int                connfd;
    pid_t              childpid;
    socklen_t          clilen;
    struct sockaddr_in cliaddr;
    struct sockaddr_in servaddr;

    // listenfd = Socket(AF_INET, SOCK_STREAM, 0);
    if ((listenfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
        err_sys("socket error");

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family      = AF_INET; // 如果是多宿，我们将接受目的地址为任何本地接口的连接
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    std::cout << SERV_PORT << std::endl;
    servaddr.sin_port        = htons(SERV_PORT);

    // Bind(listenfd, (SA*)&servaddr, sizeof(servaddr));
    if (bind(listenfd, (sockaddr*)&servaddr, sizeof(servaddr)) < 0)
    {
        err_sys("bind error");
    }

    // Listen(listenfd, LISTENQ); // 转换为监听套接字
    if (listen(listenfd, LISTENQ) < 0)
    {
        err_sys("listen error");
    }

    Signal(SIGCHLD, sig_chld);

    for ( ; ; )
    {
        clilen = sizeof(cliaddr);
        // connfd = Accept(listenfd, (SA *) &cliaddr, &len);
        if ((connfd = accept(listenfd, (sockaddr*)&cliaddr, &clilen)) < 0)
        {
            if (errno == EINTR)
            {
            	continue;
            }
#ifdef  EPROTO
            if (errno == EPROTO || errno == ECONNABORTED)
#else
                if (errno == ECONNABORTED)
#endif
                    continue;
                else
                    err_sys("accept error");
        }

        // clilen = sizeof(cliaddr);
        // 服务器阻塞于accept调用，等待客户连接的完成
        // connfd = Accept(listenfd, (SA *) &cliaddr, &clilen);
        // fork为每个客户派生一个处理它们的子进程，子关闭监听套接字，父关闭已连接套接字
        if ((childpid = fork()) == -1)
            err_sys("fork error");
        if (0 == childpid) /* child process */
        {
            // Close(listenfd);    /* close listening socket */
            if (close(listenfd) == -1)
            {
                err_sys("close error");
            }
            str_echo(connfd);   /* process the request */
            std::cout << "exiting tcpserv01 child process" << std::endl;
            // 服务器子进程调用exit来终止。服务器子进程中打开的所有描述符随之关闭，
            // 这会导致TCP连接终止序列
            // 的最后两个分节：一个从服务器到客户的FIN，和，一个从客户到服务器的ACK，至此，
            // 连接完全终止，客户套结字进入TIME_WAIT状态。

            // 另一方面
            // when this child is existed, this process will send sigchild signal to parent process
            // and in the parent process, we did not handle this signal, so the child process,
            // this process will be a zombie process, we can see that by command ps ux
            // exit(0);
            return 0;
        }
        // Close(connfd); /* parent closes connected socket */
        if (close(connfd) == -1)
        {
            err_sys("close error");
        }
    }
}

#include "../lib/unpsunyj.h"

void sig_chld(int signo)
{
    pid_t pid;
    int   stat;

    pid = wait(&stat);
    printf("child %d terminated
", pid);
    return;
}

/* include unph */
/* Our own header.  Tabs are set for 4 spaces, not 8 */

#ifndef	__unp_h
#define	__unp_h

#include <stdlib.h>
#include <errno.h>
#include <stdio.h>
#include <cstring>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <signal.h>
#include <sys/wait.h>

#include "../config.h" /* configuration options for current OS */
                       /* "../config.h" is generated by configure */
/* Miscellaneous constants */
#define MAXLINE  4096 /* max text line length */
#define BUFFSIZE 8192 /* buffer size for reads and writes */
#define LISTENQ  1024 /* 2nd argument to listen() */

/* Define some port number that can be used for our examples */
#define SERV_PORT       9877              /* TCP and UDP */
#define SERV_PORT_STR   "9877"            /* TCP and UDP */
#define UNIXSTR_PATH    "/tmp/unix.str"   /* Unix domain stream */
#define UNIXDG_PATH     "/tmp/unix.dg"    /* Unix domain datagram */

typedef void Sigfunc(int);   /* for signal handlers */
Sigfunc* Signal(int signo, Sigfunc *func); /* for our signal() function */
void sig_chld(int);


void err_dump(const char *, ...);
void err_msg(const char *, ...);
void err_quit(const char *, ...);
void err_ret(const char *, ...);
void err_sys(const char *, ...);

void str_echo(int sockfd);
void str_cli(FILE *fp, int sockfd);

char* Fgets(char *ptr, int n, FILE *stream);
void Fputs(const char *ptr, FILE *stream);

ssize_t Readline(int fd, void *ptr, size_t maxlen);

void Writen(int, void *, size_t);

#endif	/* __unp_h */