signal, page 342

signal 예제. shell에서 kill -l로 해당 PID에 시그널을 보낼 수 있다.

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
/* handler for SIGINT */


static void signal_hanlder (int signo)
{
/*
* Technically, you shouldn't use printf() in a
* signal handler, but it isn't the end of the
* world. I'll discuss why in the section
* "Reentrancy."
*/
	if(signo == SIGINT){
		printf ("Caught SIGINT!\n");
		exit (EXIT_SUCCESS);
	}
	else if(signo == SIGCHLD){
		printf ("SIGCHLD occured!\n");
		//exit (EXIT_SUCCESS);

	}
}

static void sigchld_handler (int signo)
{
/*
* Technically, you shouldn't use printf() in a
* signal handler, but it isn't the end of the
* world. I'll discuss why in the section
* "Reentrancy."
*/
	printf ("SIGCHLD occured!\n");
	//exit (EXIT_SUCCESS);
}

static void sighup_handler (int signo)
{
/*
* Technically, you shouldn't use printf() in a
* signal handler, but it isn't the end of the
* world. I'll discuss why in the section
* "Reentrancy."
*/
	printf ("SIGHUP occured!\n");
	printf ("ignoring SIGHUP\n");
	if (signal(SIGHUP, SIG_IGN) == SIG_ERR){
		fprintf (stderr, "Cannot ignore SIGHUP!\n");
		exit (EXIT_FAILURE);
	}

}


int main (void)
	{
	/*
	* Register signal_hanlder as our signal handler
	* for SIGINT.
	*/
	int pid;

	if (signal (SIGINT, signal_hanlder) == SIG_ERR) {
		fprintf (stderr, "Cannot handle SIGINT!\n");
		exit (EXIT_FAILURE);
	}
	if (signal(SIGCHLD, signal_hanlder) == SIG_ERR){
		fprintf (stderr, "Cannot handle SIGCHLD!\n");
		exit (EXIT_FAILURE);

	}

	//signal hangup 등록
	//주석 처리 후 run.. shell로 signal 전송.
	//pi@raspberrypi:~ $ kill -1 pid
	//하면 
	//pi@raspberrypi:~/Project/cCode/systemProgram $ rm ./a.out ;gcc signal.c ;./a.out
	//I'm child, died
	//SIGCHLD occured!
	//끊어짐
	//주석 처리하면
	//pi@raspberrypi:~ $ kill -1 pid
	//하면 무시함.

	if (signal(SIGHUP, SIG_IGN) == SIG_ERR){
		fprintf (stderr, "Cannot ignore SIGHUP!\n");
		exit (EXIT_FAILURE);
	}


	//더 이어서..
	//한번 sighup을 주면 메세지를 주고,
	//두번째 받으면 무시되도록 작성.
	if (signal(SIGHUP, sighup_handler) == SIG_ERR){
		fprintf (stderr, "Cannot redefine SIGHUP!\n");
		exit (EXIT_FAILURE);
	}

	pid=fork();

	if(pid == 0){
		//child process
		printf("I'm child, died\n");
		sleep(1);
		_exit(EXIT_SUCCESS);
	}

	for (;;)
		pause ();

	return 0;
}