Continue executing a stopped process with SIGALRM in C - c

Question

the job is to continue executing a child process I stopped when I receive a SIGALRM signal.
so far I did the following, which doesn't seems to work:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <sys/wait.h>
void handler(int sig)
{
printf("hello from the handler\n");
kill(getpid(),SIGCONT);
printf("child is continuing executing");
}
int main()
{
int pid1=fork();
signal(SIGALRM,handler);
if (pid1==0) {
kill(getpid(),SIGTSTP);
printf(" I am in the child\n");
} else {
printf("i am in the parent \n");
kill(pid1,SIGALRM);
}
}
I've tried many variations of the code, but printf("I am in the child"); is never executed.

Answer 1

Re: the question asked in a comment is ("how can I make the kill(pid1,SIGALRM) send the signal to the child?"). The call kill(pid1,SIGALRM) does send the signal to the child, but the child does not respond to it because it is stopped. The question asked is somewhat ambiguous, as it is not clear who "I" refers to in the phrase "when I receive a SIGALRM signal". If you want to have the child continue when the child receives a SIGALRM, you can't. You must send the child a SIGCONT before it will do anything. If you want the child to continue when the parent receives the SIGALRM, you could so something like:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <sys/wait.h>
pid_t pid1;
void handler(int sig)
{
(void)sig;
if( pid1 ) {
kill(pid1, SIGCONT);
}
}
int main(void)
{
signal(SIGALRM, handler);
pid1 = fork();
if( pid1 == 0 ) {
kill(getpid(), SIGTSTP);
printf("Child continued\n");
} else {
alarm(1);
pause();
}
}