How to make parent wait for all child processes to finish?

Question

I'm hoping someone could shed some light on how to make the parent wait for ALL child processes to finish before continuing after the fork. I have cleanup code which I want to run but the child processes need to have returned before this can happen.

for (int id=0; id<n; id++) {   if (fork()==0) {     // Child     exit(0);         } else {     // Parent     ...   }   ... } 

Answer 1

pid_t child_pid, wpid; int status = 0;  //Father code (before child processes start)  for (int id=0; id<n; id++) {     if ((child_pid = fork()) == 0) {         //child code         exit(0);     } }  while ((wpid = wait(&status)) > 0); // this way, the father waits for all the child processes   //Father code (After all child processes end) 

wait waits for a child process to terminate, and returns that child process's pid. On error (eg when there are no child processes), -1 is returned. So, basically, the code keeps waiting for child processes to finish, until the waiting errors out, and then you know they are all finished.

Answer 2

POSIX defines a function: wait(NULL)；. It's the shorthand for waitpid(-1, NULL, 0);, which will suspends the execution of the calling process until any one child process exits. Here, 1st argument of waitpid indicates wait for any child process to end.

In your case, have the parent call it from within your else branch.