fork() and exec() run in parallel in C - c

Question

I am trying to run three execv("./test",execv_str) in parallel. And I need to print out success message when each of execv() completes successfully.
But now I get result as following:
username#username:~/Desktop/$./test -p
SUCCESS
SUCCESS
SUCCESS
username#username:~/Desktop/$ TESTING
TESTING
TESTING
The expected result will be:
username#username:~/Desktop/$./test -p
TESTING
SUCCESS
TESTING
SUCCESS
TESTING
SUCCESS
username#username:~/Desktop/$
Here is the code.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
int fork_execv()
{
int status;
pid_t pid;
pid = fork();
/* Handling Child Process */
if(pid == 0){
char* execv_str[] = {"./test", NULL};
if (execv("./test",execv_str) < 0){
status = -1;
perror("ERROR\n");
}
}
/* Handling Child Process Failure */
else if(pid < 0){
status = -1;
perror("ERROR\n");
}
return status;
}
int main(int argc, char *argv[]){
if (argc == 1){
sleep(5);
printf("TESTING\n");
}
else{
int i;
for(i = 0; i < 3; ++i){
if (fork_execv() != -1){
printf("SUCCESS\n");
}
}
}
}
How to modify my code to make it work?

Answer 1

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
int fork_execv()
{
int status;
pid_t pid;
pid = fork();
/* Handeling Chile Process */
if(pid == 0){
char* execv_str[] = {"./test", NULL};
if (execv("./test",execv_str) < 0){
status = -1;
perror("ERROR\n");
}
}
/* Handeling Chile Process Failure */
else if(pid < 0){
status = -1;
perror("ERROR\n");
}
return pid;
}
void handler(int sig){
printf("SUCCESS\n");
}
int main(int argc, char *argv[]){
if (argc == 1){
sleep(5);
printf("TESTING\n");
}
else{
int i;
pid_t process_id;
for(i = 0; i < 3; ++i){
if ((process_id = fork_execv()) != -1){
if(process_id != 0){
signal(SIGCHLD, handler);
waitpid(process_id, NULL, 0);
}
}
}
}
}
Here what I would do. After the fork, I return the pid, check if it isn't 0 (so we are in the father process) and make the father wait for the son. To print "success", I bind the SIGCHLD signal that is triggered when a child process ends. Note that this is a little overkill and put print after the waitpid would have done the job. (But I like to bind signal.)