Signal Programming

// signal1.c
#include<stdio.h>
#include<signal.h>
#include<unistd.h>

void signalHandler(int signo) {
	if (signo == SIGINT)
		printf(" received SIGINT\n");
}

int main(void) {
	printf("My pid is %d.\n", getpid());
	if (signal(SIGINT, signalHandler) == SIG_ERR)
		printf("\n Can't catch SIGINT\n");
// A long long wait so that we can easily issue a signal to this process
	while (1)
		sleep(1);
	return 0;
}

// signal2.c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <signal.h>

void HandlerChild() {
	printf("Sigint received by child \n");
}

void HandlerParent() {
	printf("Sigint received by Parent \n");
	signal(SIGINT, HandlerParent);
}

int n, statusp;

int main(void) {
// signal(SIGINT,HandlerParent);
	n = fork();
	if (n == 0) {
		printf("Child ID %d\n", getpid());
		signal(SIGINT, HandlerChild);
		for (;;) {
		};
	} else {
		printf("Parent ID %d \n", getpid());
// signal(SIGINT,HandlerParent);
		wait(&statusp);
// kill(n,SIGKILL);
		exit(0);
	}
	return 0;
}

$ gcc -o signal2 signal2.c -Wall 
$ ./signal2
Parent ID 4564 
Child ID 4565
^CSigint received by child 

// signal3.c
#include <stdio.h>
#include <signal.h>
#include <unistd.h>

int r, count = 0, n;

void HL_AlarmSig(int al) {
	printf(" I am active every 5 sec ");

	signal(SIGALRM, HL_AlarmSig);
	r = alarm(5);
	count++;
	printf(" .... Now the time is %d sec \n", count * 5);
}

void HL_AllSig(int s) {
	printf(" Oh ! I just received signal number %d \n", s);
	signal(s, HL_AllSig);
}

int main(void) {
	for (n = 1; n <= 31; n++) {
		signal(n, HL_AllSig);
	}
	signal(SIGALRM, HL_AlarmSig);
	r = alarm(5);
	while (count < 12) {
	};
	printf(" Program Terminate !! ");
	return 0;
}

$ gcc -o signal3 signal3.c -Wall 

$ ./signal3
^C Oh ! I just received signal number 2 
^C Oh ! I just received signal number 2 
^C Oh ! I just received signal number 2 
 I am active every 5 sec  .... Now the time is 5 sec 
^Z Oh ! I just received signal number 20 
^\ Oh ! I just received signal number 3 
 I am active every 5 sec  .... Now the time is 10 sec 
 I am active every 5 sec  .... Now the time is 15 sec 
^C Oh ! I just received signal number 2 
^C Oh ! I just received signal number 2 
^C Oh ! I just received signal number 2 
^Z Oh ! I just received signal number 20 
^Z Oh ! I just received signal number 20 
 I am active every 5 sec  .... Now the time is 20 sec 
 I am active every 5 sec  .... Now the time is 25 sec 
 I am active every 5 sec  .... Now the time is 30 sec 


 I am active every 5 sec  .... Now the time is 35 sec 
 I am active every 5 sec  .... Now the time is 40 sec 
 I am active every 5 sec  .... Now the time is 45 sec 
 I am active every 5 sec  .... Now the time is 50 sec 
 I am active every 5 sec  .... Now the time is 55 sec 
 I am active every 5 sec  .... Now the time is 60 sec 

// signal4.c
#include <stdio.h>
#include <signal.h>
#include <unistd.h>

int r, n;

void HL_AlarmSig(int al) {
	printf(" Every 5 sec I have to tell you this PID \n");
	printf(" ....... THIS PROCESS ID = %d ....... \n", getpid());
	signal(SIGALRM, HL_AlarmSig);
	r = alarm(5);

}
void Nothing(int s) {
	signal(s, Nothing);
}

void InfiniteLoop(int s) {
	printf(" No ! I don't care signal number %d  \n", s);
	printf("If you want to stop this process send signal number 9 ONLY!!!\n");

	signal(s, InfiniteLoop);
	for (;;) {
		printf("Loop\n");
	}; /* infinite loop */

}

int main(void) {

	for (n = 1; n <= 31; n++) {
		signal(n, Nothing);
	}
	signal(SIGINT, InfiniteLoop);
	signal(SIGALRM, HL_AlarmSig);
	printf(" If you want to go into the infinite loop \n");
	printf("  .......press  ^C within 5 sec...... \n ");
	r = alarm(5);
	for (;;) {
	};
	printf(" Program Terminate !! \n");
	return 0;
}

$ gcc -o signal4 signal4.c -Wall
$ ./signal4 
If you want to go into the infinite loop
  .......press  ^C within 5 sec......
  Every 5 sec I have to tell you this PID
 ....... THIS PROCESS ID = 21538 .......
 Every 5 sec I have to tell you this PID
 ....... THIS PROCESS ID = 21538 .......

(ถ้ากด Ctrl+C โปรแกรมจะเข้าลูปอนันต์)

// signal5.c
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include <sys/wait.h>

int n, status;

void HL_Child(int s) {
	printf("**Child**I received signal No. %d .. you can't kill me \n", s);
	signal(s, HL_Child);
}

void HL_Parent(int s) {
	printf("***Parent*** I received signal number %d \n", s);
	signal(s, HL_Parent);
}
void HL_Parent14(int s) {
	printf("***Parent*** I received signal No. %d == Alarm Signal \n", s);
	signal(s, HL_Parent14);

}

void HL_Child14(int s) {
	printf("***Child*** I received signal No %d == Alarm Signal \n", s);
	signal(s, HL_Child14);
}
void HL_Child3(int s) {
	printf("***Child*** I received signal No %d  .. I will exit \n", s);
	exit(5);
}

int main(void) {
	int i;
	for (i = 1; i <= 31; i++)
		signal(i, HL_Parent);
	n = fork();
	if (n == 0) /* Child Process */
	{
		for (i = 1; i <= 31; i++)
			signal(i, HL_Child);
		signal(SIGALRM, HL_Child14);
		signal(3, HL_Child3);
		alarm(2);
		printf("--c--  Child ID  = %d  \n", getpid());
		printf("--c--  Child Process goes into the infinite loop \n");
		printf("--c--  Signal number 3 (^\\) can kill me \n");
		for (;;) {
		};
	} else /* Parent Process */
	{
		printf("--p--  Parent ID  = %d  \n", getpid());
		signal(SIGALRM, HL_Parent14);
		/* alarm(2);  */
		printf("--p--  I am waiting for child exit or any signal \n");
		wait(&status);
		printf("--p--  Wait completed !!  and I am waiting again ...\n");
		wait(&status);
		printf("--p--  Wait completed !! ...exit status = %d\n", status >> 8);
		printf("--p-- I am pausing for check signal from child exit ... \n");
		pause();
		wait(&status);
		printf("--p-- Wait completed !! ...exit status = %d \n", status >> 8);
		printf("--p-- I will execute newprog now !! \n");
		for (i = 1; i <= 31; i++)
			signal(i, SIG_IGN);
		signal(3, SIG_DFL);
		signal(2, HL_Parent);
		i = execl("newprog", "newprog", 0);
		printf("--p-- Parent Process terminated !!\n");
		exit(0);

	}
	return 0;
}

$ gcc -o signal5 signal5.c -Wall
$ ./signal5 
--p--  Parent ID  = 22119
--p--  I am waiting for child exit or any signal
--c--  Child ID  = 22120
--c--  Child Process goes into the infinite loop
--c--  Signal number 3 (^\) can kill me

(กด Ctrl+C เพื่อส่งสัญญาณให้ child process)
^C***Parent*** I received signal number 2
**Child**I received signal No. 2 .. you can't kill me

(กด Ctrl+C เพื่อส่งสัญญาณให้ child process)
^C***Parent*** I received signal number 2
**Child**I received signal No. 2 .. you can't kill me
***Child*** I received signal No 14 == Alarm Signal

(กด Ctrl+Z เพื่อส่งสัญญาณให้ child process)
^Z**Child**I received signal No. 18 .. you can't kill me
***Parent*** I received signal number 18

(ถ้ากด Ctrl+\ เพื่อส่งสัญญาณให้ child process เพื่อเรียกฟังก์ชัน HL_Child3() )
^\***Parent*** I received signal number 3
***Child*** I received signal No 3  .. I will exit
***Parent*** I received signal number 20
--p--  Wait completed !!  and I am waiting again ...
--p--  Wait completed !! ...exit status = 5
--p-- I am pausing for check signal from child exit ...

(กด Ctrl+C เพื่อสั่งหยุดโปรแกรม)
^C***Parent*** I received signal number 2
--p-- Wait completed !! ...exit status = 5
--p-- I will execute newprog now !!
--p-- Parent Process terminated !!

/*
 *  signal6.c
 *  
 *  The parent process pulls a child exit status whenever the OS notifies
 *  a child status change.
 *
 *  Created by Mij <mij@bitchx.it> on 04/01/05.
 *  Original source file available at http://mij.oltrelinux.com/devel/unixprg/
 *
 */

/* for printf() and fgetc() */
#include <stdio.h>
/* for fork() */
#include <sys/types.h>
#include <unistd.h>
/* for srandom() and random() */
#include <stdlib.h>
/* for time() [seeding srandom()] */
#include <time.h>
/* for waitpid() */
#include <sys/wait.h>
/* for signal(), kill() and raise() */
#include <signal.h>

/* how many childs to raise */
#define NUM_PROCS   5

/* handler prototype for SIGCHLD */
void child_handler(int);

int main(int argc, char *argv[]) {
	int i, exit_status;

	/* execute child_handler() when receiving a signal of type SIGCHLD */
	signal(SIGCHLD, &child_handler);

	/* initialize the random num generator */
	srandom(time(NULL));

	printf("Try to issue a \'ps\' while the process is running...\n");

	/* produce NUM_PROCS childs */
	for (i = 0; i < NUM_PROCS; i++) {
		if (!fork()) {
			/* child */

			/* choosing a random exit status between 0 and 99 */
			exit_status = (int) (random() % 100);
			printf(" -> New child %d, will exit with %d.\n", (int) getpid(),
					exit_status);

			/* try to skip signals overlapping */
			sleep((unsigned int) (random() % 3));

			/* choosing a value to exit between 0 and 99 */
			exit(exit_status);
		}

		/* father */
		sleep((unsigned int) (random() % 2));
	}

	/* checkpoint */
	printf("parent: done with fork()ing.\n");

	/* why this is not equivalent to sleep(20) here? */
	for (i = 0; i < 10; i++) {
		sleep(1);
	}
	/* all the child processes should be done now */
	printf("I did not purge all the childs. Timeout; exiting.\n");

	/* terminate myself => exit */
	kill(getpid(), 15);

	/* this won't be actually executed */
	return 0;
}

/* handler definition for SIGCHLD */
void child_handler(int sig_type) {
	int child_status;
	pid_t child;
	static int call_num = 0;

	/* getting the child's exit status */
	child = waitpid(0, &child_status, 0);

	printf("<-  Child %d exited with status %d.\n", child,
			WEXITSTATUS(child_status));

	/* did we get all the childs? */
	if (++call_num >= NUM_PROCS) {
		printf("I got all the childs this time. Going to exit.\n");
		exit(0);
	}

	return;
}

$ gcc -o signal6 signal6.c -Wall

$ ./signal6 
Try to issue a 'ps' while the process is running...
 -> New child 12274, will exit with 68.
 -> New child 12275, will exit with 57.
 -> New child 12276, will exit with 96.
parent: done with fork()ing.
 -> New child 12277, will exit with 18.
 -> New child 12278, will exit with 72.
<-  Child 12275 exited with status 57.
<-  Child 12274 exited with status 68.
<-  Child 12277 exited with status 18.
<-  Child 12276 exited with status 96.
<-  Child 12278 exited with status 72.
I got all the childs this time. Going to exit.