Question

I’m playing with waitpid() and signal() and I’m looking for reliable test cases for returning WIFSIGNALED(status) = WIFSTOPPED(status) = WIFCONTINUED (status) = true but can’t find any…

Care to tell me how can I make sure those return true so I can debug my code?

Also, a few hints about what signals should I catch with signal() to test those macros would be helpful…

Answer 1

#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <unistd.h>

#define NELEMS(x) (sizeof (x) / sizeof (x)[0])

static void testsignaled(void) {
   kill(getpid(), SIGINT);
}

static void teststopped(void) {
   kill(getpid(), SIGSTOP);
}

static void testcontinued(void) {
   kill(getpid(), SIGSTOP);
   /* Busy-work to keep us from exiting before the parent waits.
    * This is a race.
    */
   alarm(1);
   while(1) {}
}

int main(void) {
   void (*test[])(void) = {testsignaled, teststopped, testcontinued};
   pid_t pid[NELEMS(test)];
   int i, status;
   for(i = 0; i < sizeof test / sizeof test[0]; ++i) {
      pid[i] = fork();
      if(0 == pid[i]) {
         test[i]();
         return 0;
      }
   }
   /* Pause to let the child processes to do their thing.
    * This is a race.
    */
   sleep(1);
   /* Observe the stoppage of the third process and continue it. */
   wait4(pid[2], &status, WUNTRACED, 0);
   kill(pid[2], SIGCONT);
   /* Wait for the child processes. */
   for(i = 0; i < NELEMS(test); ++i) {
      wait4(pid[i], &status, WCONTINUED | WUNTRACED, 0);
      printf("%d%s%s%s\n", i, WIFCONTINUED(status) ? " CONTINUED" : "", WIFSIGNALED(status) ? " SIGNALED" : "", WIFSTOPPED(status) ? " STOPPED" : "");
   }
   return 0;
}