How to terminate a c program after 20 seconds - c

Question

I am trying to terminate my c program with multiple functions after 20 seconds (kill all child and parent processes, close files). I tried alarm(), itimer(), clock(). It works when we only have a main and a handler function. clock() restarts from 0 in every function even if I keep the variables global.
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <time.h>
#include <stdlib.h>
#include <dirent.h>
#include <stdio.h>
#include <string.h>
#include <getopt.h>
#include<stdbool.h>
#include <ctype.h>
#include<sys/wait.h>
#include<signal.h>
#include <sys/mman.h>
#include<sys/time.h>
#define INTERVAL 2
int t=0;
void display_message()
{
printf("In the handler");
//kill(0,SIGKILL);
t=1;
}
void calling2()
{
signal(SIGALRM, display_message);
sleep(3);
}
void calling()
{
signal(SIGALRM, display_message);
alarm(2);
int i;
for(i=0;i<3;i++)
{
//printf("\nStarting fork for loop i=%d \n",i);
pid_t pID = fork();
if (pID == 0) // child
{
calling2();
if(t==1)
{
printf("we have exceeded 2 seconds killing the process");
kill(0,SIGKILL);
exit(0);
}
exit(0);
kill(pID,SIGKILL);
}
else if(pID>0)
{
// printf("\nhello from the father");
if(t==1)
{
printf("killing the process");
kill(0,SIGKILL);
exit(0);
}
printf("\nhello from the father");
}
}
}
As you can see I tried calling signal from different functions so it can catch the signal and the handler can execute but the handler is never executed.
EDIT: Tried this again
# include <unistd.h>
# include <sys/types.h>
# include <sys/stat.h>
# include <time.h>
# include <stdlib.h>
# include <dirent.h>
# include <stdio.h>
# include <string.h>
# include <getopt.h>
# include<stdbool.h>
# include <ctype.h>
# include<sys/wait.h>
# include<signal.h>
# include <sys/mman.h>
# include<sys/time.h>
# define INTERVAL 2
int t=0;
void display_message()
{
kill(0,SIGKILL);
t=1;
}
void calling2()
{
sleep(3);
}
void calling()
{
signal(SIGALRM, display_message);
int i;
for(i=0;i<3;i++)
{
pid_t pID = fork();
if (pID == 0) // child
{
calling2();
if(t==1)
{
printf("killing the process");
kill(0,SIGKILL);
exit(0);
}
exit(0);
}
else if(pID>0)
{
if(t==1)
{
printf("killing the process");
kill(0,SIGKILL);
exit(0);
}
printf("\nhello from the father");
}
}
}
int main()
{
signal(SIGALRM, display_message);
alarm(2);
calling();
}
O/P:
hello from the father
hello from the father
hello from the father
hello from the father
hello from the father
hello from the father
error: Failed with return code 22

Answer 1

Main problem is your main thread is finished before alarm signal is handled. You must let it live at least until alarm signal is delivered. Also as Jonathan Leffler adviced good indentation/spacing is really helpful.
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <time.h>
#include <stdlib.h>
#include <dirent.h>
#include <stdio.h>
#include <string.h>
#include <getopt.h>
#include <stdbool.h>
#include <ctype.h>
#include <sys/wait.h>
#include <signal.h>
#include <sys/mman.h>
#include <sys/time.h>
#define INTERVAL 2
int t=0;
void display_message()
{
kill(0,SIGKILL);
t=1;
}
void calling2()
{
sleep(3);
}
void calling()
{
signal(SIGALRM, display_message);
int i;
for(i=0;i<3;i++)
{
pid_t pID = fork();
if (pID == 0) // child
{
calling2();
if(t==1)
{
printf("killing the process");
kill(0,SIGKILL);
exit(0);
}
exit(0);
}
else if(pID>0)
{
if(t==1)
{
printf("killing the process");
kill(0,SIGKILL);
exit(0);
}
printf("\nhello from the father");
}
}
}
int main()
{
signal(SIGALRM, display_message);
alarm(2);
calling();
// wait until alarm callback before terminating main thread
sleep(100);
}