Measure the time of a child process without blocking the parent - fork

Question

I want to measure the execution time of a child process. I can use times function
https://linux.die.net/man/3/times. But it requires to block the parent process using wait(). On the other hand, I need to keep the parent process running in parallel to store the data being generated by the child. Once the child has exited, I want to know how much CPU time was spent in executing the child process. Something like below:
int done = FALSE;
struct timespec ts;
struct rusage ru;
struct timeval utime;
struct timeval stime;
int main(int argc, char* argv[]){
pid_t pid1, pid2; int status;
char *args[] = {"./wp"};
struct rusage usage;
int i, j,n;
signal(SIGCHLD,reaper);
pid1 = fork();
if (pid1 == 0) { // child
printf("Its child %d\n",getpid());
printf("child %d: executing target program\n", getpid());
execv(argv[1], argv+1);
}
n = 0;
while (n<20) { //parent has to do some stuff in parallel
printf("doing something...\n"); sleep(1);
if (done){ // child exited
done = FALSE;
pid_t pid2 = wait3(&status, 0, &usage);
printf("...child of %d done executing.\n",getpid());
printf("exit code for %d is %d\n", pid2, status);
if (WIFEXITED(status))
printf("The exit status is %d\n", WEXITSTATUS(status));
utime = usage.ru_utime;
stime = usage.ru_stime;
printf("RUSAGE :ru_utime => %lld [sec] : %lld [usec], :ru_stime => %lld [sec] : %lld [usec] \n",
(int64_t)utime.tv_sec, (int64_t)utime.tv_usec,
(int64_t)stime.tv_sec, (int64_t)stime.tv_usec);
}
n++;
}
printf("got my SIGCHLD, cleaning up!\n");
signal(SIGCHLD,SIG_DFL);
return 0;
}
void reaper(int sig) {
done=TRUE; //
}