Cleaning Up Children Asynchronously

• An easy way to clean up child processes is by handling SIGCHLD.
• The following program is what it looks like for a program to use a SIGCHLD handler to clean up its child processes.

  #include <signal.h>
  #include <string.h>
  #include <sys/types.h>
  #include <sys/wait.h>
  
  sig_atomic_t child_exit_status;
  
  void clean_up_child_process (int signal_number)
  {
    /* Clean up the child process.  */
    int status;
    wait (&status);
    /* Store its exit status in a global variable.  */
    child_exit_status = status;
  }
  
  int main ()
  {
    /* Handle SIGCHLD by calling clean_up_child_process.  */
    struct sigaction sigchld_action;
    memset (&sigchld_action, 0, sizeof (sigchld_action));
    sigchld_action.sa_handler = &clean_up_child_process;
    sigaction (SIGCHLD, &sigchld_action, NULL);
  
    /* Now do things, including forking a child process.  */
    /* ...  */
  
    return 0;
  }
  

• Note how the signal handler stores the child process's exit status in a global variable, from which the main program can access it. Because the variable is assigned in a signal handler, its type is sig_atomic_t.