How to make multiple child proccess pause until a signal is sent - c

Question

I have a program with three child processes all doing the exact same thing with a fourth child process told send signals while the main function waits until the three child processes are complete. I am using an alarm signal as well as two user signals to make the child process send output to a different terminal. I'm using the pause function to wait for a signal but the second I start the program it completes, not waiting at all. Am I using pause correctly?
int alarmR =0;
int SNMPR =0;
int reconR=0;
int child_pid[4];
char strD[100];
FILE *fpt[4];
void Alarmhandler(int sig);
void Reconfigure(int sig);
void SNMPhandler(int sig);
int which(int wait_ret, int child_proc[], int p);
void IT1(void);
void IT2(void);
void IT3(void);
void command(void);
void command(void)
{
signal(SIGALRM,Alarmhandler);
signal(SIGUSR1,Reconfigure );
signal(SIGUSR2,SNMPhandler );
char text;
int n;
printf("please enter a command from the following list\n");
printf("\tsn:Send a SNMP request\n\trn:Send a reconfiguration");
printf("script\n\tkn: shutdown process\n");
scanf("%c%d",&text,&n);
if(text == 'k')
{
printf("Terminated IT service %d\n",n);
n = n-1;
kill(child_pid[n],1);
}
else if(text=='s')
{
n = n-1;
kill(child_pid[n],SIGUSR2);
}
else if(text=='r')
{
n = n-1;
kill(child_pid[n],SIGUSR1);
}
}
void Alarmhandler(int sig)
{
alarmR =1;
}
void Reconfigure(int sig)
{
reconR =1;
}
void SNMPhandler(int sig)
{
SNMPR =1;
}
int which(int wait_ret, int child_proc[], int p)
{
int i;
for (i = 0; i < p; i++)
if (child_proc[i] == wait_ret)
return i;
return -1;
}
int main(int argc, char *argv[])
{
int ttyindex;
// int Terminal[4];
int term_cnt = 0;
int wait_r,x;
int process = 0;
int child_proc[4];
int es[3];
if(argc != 5) {
printf("Usage: ./lab7 1 2 3 4\n");
exit(1);
}
for(term_cnt =0; term_cnt <4;term_cnt ++)
{
ttyindex = -1;
ttyindex = atoi(argv[term_cnt+1]);
if (ttyindex < 1) {
printf("invalid terminal number %s\n", argv[term_cnt+1]);
exit(1);
}
sprintf(strD, "/dev/pts/%d", ttyindex);
child_proc[process] = fork();
if (child_proc[process] != 0)
{
// parent process
process++;
child_proc[process] = fork();
if (child_proc[process] != 0)
{
// parent process
process++;
child_proc[process] = fork();
if (child_proc[process] != 0)
{
// parent process
process++;
child_proc[process] = fork();
if(child_proc[process] !=0)
{
wait_r = wait(NULL);
x =which(wait_r, child_proc, process);
printf("Waited for %d (child %d) to finish.\n", wait_r,x);
if(WIFEXITED(wait_r))
{
es[x] = WEXITSTATUS(wait_r);
}
wait_r = wait(NULL);
x =which(wait_r, child_proc, process);
printf("Waited for %d (child %d) to finish.\n", wait_r,x);
if(WIFEXITED(wait_r))
{
es[x] = WEXITSTATUS(wait_r);
}
wait_r = wait(NULL);
x =which(wait_r, child_proc, process);
printf("Waited for %d (child %d) to finish.\n", wait_r,x);
if(WIFEXITED(wait_r))
{
es[x] = WEXITSTATUS(wait_r);
}
for(x = 0; x <3;x++)
{
if(es[x] == 0)
{
printf("\nJob well done IT specialist %d",(x+1));
printf(" Prepare for new attacks!\n");
}
else if(es[x] == 1)
{
printf("\nIT service %d compromised",(x+1));
printf(" , we are going out of business!\n");
}
else
{
printf("\nCall HR, we need a new");
printf(" cybersecurity expert for service");
printf(" %d\n",(x+1));
}
}
}
else
{
child_pid[3] = getpid();
command();
}
}
else
{
child_pid[2]=getpid();
IT3();
}
}
else
{
child_pid[1] = getpid();
IT2();
}
}
else
{
child_pid[0] = getpid();
IT1();
}
}
void IT1(void)
{
printf("i live");
signal(SIGALRM,Alarmhandler);
signal(SIGUSR1,Reconfigure );
signal(SIGUSR2,SNMPhandler );
clock_t start=0, end=0;
static int check = 0;
static int recona =0;
double t= 0;
int threat= 1;
srand48(time(NULL));
fprintf(fpt[1],"This is IT service 1\n");
while(1)
{
printf("%d %d %d",reconR,alarmR,SNMPR);
pause();
// alarm(1);
if(reconR == 1)
{
reconR =0;
if(recona >0)
{
fprintf(fpt[1],"Cannot reconfigure more than once.you are fired!");
exit(1);
}
if(threat < 16)
{
fprintf(fpt[1],"Threat level is not critical.you are fired");
exit(1);
}
fprintf(fpt[1],"Reconfiguring system to thwart attack-this may take a few seconds\n");
recona++;
}
if(alarmR == 1 )
{
if(check >0)
{
t =((double)(end - start))/CLOCKS_PER_SEC;
}
alarmR = 0;
if(recona >0)
{
threat --;
}
else
{
if (drand48() < 0.5)
{
threat++;
}
else if (threat > 1 && drand48() < 0.6)
{
threat--;
}
}
if(t <5)
{
fprintf(fpt[1],"Next report available in %f seconds\n",(5-t));
}
if(threat >15)
{
fprintf(fpt[1],"Intruder! Data stolen...");
exit(1);
}
else if(threat < 10 && recona >0)
{
fprintf(fpt[1],"Attack averted. Mission Complete");
exit(0);
}
}
if(SNMPR == 1)
{
if(check == 2)
{
end = clock();
t = ((double)(end - start))/CLOCKS_PER_SEC;
}
SNMPR = 0;
check = 1;
if(t <5)
{
fprintf(fpt[1],"Load to high. Threat is increased");
threat++;
t = 0;
}
else{
if(threat >=10)
fprintf(fpt[1],"Threat level is red\n");
else if(threat <10 && threat >=5)
fprintf(fpt[1],"Threat level is orange\n");
else
fprintf(fpt[1],"Threat level is green\n");
}
if(check ==1)
{
start = clock();
check = 2;
}
}
}
}

Answer 1

you can use the sigsuspend() system call to make a process wait for a signal, and kill() for sending signal to a process or process group.I hope by using both of these system calls, you can code your desired task.

Answer 2

you are putting a wait() on a process which has no child here
wait_r = wait(NULL);
This causes that wait() return immediately with error ECHILD and terminates the fourth child process. It's termination raises SIGCHLD causes pause() to return.