fork-leak.c

/* 

  macOS fork bug reproducer for https://github.com/golang/go/issues/33565
  
  cc -o fork-leak fork-leak.c
  while true; do sh -c 'exec ./fork-leak 1 $$'; done

  In another terminal, run:

  while sleep 2; do pgrep fork-leak; done

  What happens, if you're on the "right" version of macOS, is that
  at some point you seeing leaked forked 'fork-leak' processes.
  This unexpected because as you can see below in do_fork, the fork
  should immediately exit. Why do some of them not exit?

  macos 10.14.5
  
*/

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

void *do_fork(void *arg) {
  if (!fork()) {
    printf("fork happened!\n");
    exit(0);
  }

  return NULL;
}

void check_err(int err, char *msg) {
  if (!err) {
    return;
  }

  printf("%s: %d\n", msg, err);
  exit(1);
}

int main(int argc, char **argv) {
  pthread_t tid;
  useconds_t wait_time;

  if (argc < 2) {
    printf("usage: %s SLEEP_US\n", argv[0]);
    exit(1);
  }

  wait_time = atoi(argv[1]);

  check_err(pthread_create(&tid, NULL, do_fork, NULL), "pthread_create");
  // check_err(pthread_join(tid, NULL), "pthread_join");
  usleep(wait_time);
  
  return 0;
}

Cross-referencing: this is a C reproducer for golang/go#33565