SIGUSR1 - kill sigaction in C - c

Question

In the C language create a program that creates two processes and connects them via pipe.
The first descendant redirects its' stdout into the pipe and writes (space separated) pairs of random numbers into it (function rand). Delay the output of the numbers by 1 second.
The second descendant redirects the pipe output to it's stdin, redirects it's stdout into a file called out.txt in the current directory.
The parent process waits 5 seconds and then sends SIGUSR1 to the first process (number generator). This should perform a correct termination of both processes. It waits for the sub-processes to terminate (wait function) and terminates itself.
I really need help with:
The first descendant has to treat the SIGUSR1 signal (sigaction function) and in case of receiving such signal it prints a string “TERMINATED” to it's stderr and terminates.
FILE *file;
file = fopen(NAZEV, "a+");
int pipefd[2];
pipe(pipefd);
pid_t pid1;
int retcode;
pid1=fork();
if(pid1 == 0) // child 1
{
close(roura[0]);
printf("child1...\n");
dup2(roura[1], STDOUT_FILENO);
int i = 0;
while(i < 6)
{
i++;
int a = rand();
int b = rand();
sleep(1);
printf("%d %d\n", a, b);
}
close(roura[1]);
exit(45);
}
else if (pid1 < 0)
{
printf("Fork selhal\n");
exit(2);
}
else
{
pid_t pid2;
pid2 = fork();
if (pid2 == 0) //child 2
{
close(roura[1]);
dup2(roura[0], STDIN_FILENO);
printf("child2...\n");
int i = 0;
while(i < 5)
{
i++;
int c;
int d;
scanf("%d %d", &c, &d);
printf("%d %d\n", c, d);
fprintf(file,"%d %d\n", c, d);
}
printf("child2 end\n");
exit(0);
}
else if (pid2 < 0)
{
printf("Fork error\n");
exit(2);
}else
{
sleep(5);
kill(pid1, SIGUSR1);
wait(&pid1); //wait for child 1
wait(&pid2); //wait for child 2
printf("parent end\n");
exit(0);
}
}
exit(0);
}

Answer 1

Adda signal handler to sigusr1 that prints to stderr and exits.
Try this, adapted to compile in cygwin:
#include <stdio.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#ifndef STDIN_FILENO
# define STDIN_FILENO 0
#endif
#ifndef STDOUT_FILENO
# define STDOUT_FILENO 1
#endif
void sig_handler(){
fprintf(stderr,"TERMINATED");
exit(0);
}
void main(int argc, char ** argv){
FILE *file;
file = fopen("NAZEV", "a+");
int pipefd[2];
int roura[2] ;
pipe(pipefd);
pid_t pid1;
int retcode;
pid1=fork();
if(pid1 == 0) // child 1
{
close(roura[0]);
printf("child1...\n");
dup2(roura[1], STDOUT_FILENO);
if (signal(SIGUSR1, sig_handler) == SIG_ERR){
printf("\ncan't catch SIGUSR1\n");
exit(13);
}
int i = 0;
while(i < 6)
{
i++;
int a = rand();
int b = rand();
sleep(1);
printf("%d %d\n", a, b);
}
close(roura[1]);
exit(45);
}
else if (pid1 < 0)
{
printf("Fork selhal\n");
exit(2);
}
else
{
pid_t pid2;
pid2 = fork();
if (pid2 == 0) //child 2
{
close(roura[1]);
dup2(roura[0], STDIN_FILENO);
printf("child2...\n");
int i = 0;
while(i < 5)
{
i++;
int c;
int d;
scanf("%d %d", &c, &d);
printf("%d %d\n", c, d);
fprintf(file,"%d %d\n", c, d);
}
printf("child2 end\n");
exit(0);
}
else if (pid2 < 0)
{
printf("Fork error\n");
exit(2);
}else
{
sleep(5);
kill(pid1, SIGUSR1);
wait(&pid1); //wait for child 1
wait(&pid2); //wait for child 2
printf("parent end\n");
exit(0);
}
}
exit(0);
}

Answer 2

You need to register a signal handler using sigaction if you want to override the default action. For SIGUSR1, the default action is to terminate the process.