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\n", 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 */
