SIGCHLD bug with macOS mach xnu posix_spawn

mach-sigchld-bug.c

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/*
This test demonstrates a case in which the macOS xnu mach kernel will reliably
fail to deliver the SIGCHLD signal most of the time.
*/

#include <unistd.h>
#include <sys/wait.h>
#include <stdio.h>
#include <string.h>
#include <spawn.h>
#include <errno.h>
#include "assert.h"

static volatile int exit_cb_called;

void sig_chld(int sig) {
  const char* msg = "SIGCHLD\n";
  write(2, msg, strlen(msg));
  exit_cb_called++;
}

int main(void) {
  pid_t pid;
  char *args[4];
  int status;

  signal(SIGCHLD, sig_chld);

  args[0] = "sh";
  args[1] = "-c";
  args[2] = "exit 12";
  args[3] = NULL;

  int r = posix_spawn(&pid, "/bin/sh", NULL, NULL, args, NULL);
  assert(r == 0);

  for (int i = 0; i < 1000; i++) {
    pid_t pid;
    int r = posix_spawn(&pid, "does not exist", NULL, NULL, args, NULL);
    assert(r == ENOENT);
  }

  assert(sleep(2) >= 0);
  assert(exit_cb_called);
  printf("exit_cb_called: %d\n", exit_cb_called);

  //do {
    r = waitpid(pid, &status, 0);
  //} while (r == -1 && errno == EINTR);
  assert(r == pid);
  r = WIFEXITED(status);
  assert(r);
  r = WEXITSTATUS(status);
  assert(r == 12);

  return 0;
}