#include <atomic>
#include <iostream>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

using namespace std;

atomic<bool> childRunning;

static void SIGCHLD_handler(int /*sig*/) {
   int status;
   pid_t childPid=wait(&status);
   // now the child with process id childPid is dead
   childRunning=false;
}

int main() {
   struct sigaction sa;
   sigemptyset(&sa.sa_mask);
   sa.sa_flags=0;
   sa.sa_handler=SIGCHLD_handler;
   sigaction(SIGCHLD,&sa,NULL);

   for (unsigned i=0; i<10; i++) {
      childRunning=true;
      pid_t pid=fork();
      if (pid) { // parent
         while (childRunning); // wait for child
      } else { // forked child
         cout << "I'm child number " << i << endl;
         usleep(500000);
         return 0; // child is finished
      }
   }

   return 0;
}