Simple C shim to reproduce issues caused by non-blocking STDIO

main.c

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

void make_nonblocking(int fd) {
  int flags = fcntl(fd, F_GETFL, 0);
  if (flags == -1) {
    perror("fcntl(F_GETFL)");
    exit(1);
  }
  if (fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1) {
    perror("fcntl(F_SETFL)");
    exit(1);
  }
}

int main(int argc, char *argv[]) {
  if (argc < 2) {
    fprintf(stderr, "Usage: %s <program> [args...]\n", argv[0]);
    exit(1);
  }

  make_nonblocking(STDIN_FILENO);
  make_nonblocking(STDOUT_FILENO);
  make_nonblocking(STDERR_FILENO);

  execvp(argv[1], &argv[1]);

  // execvp only returns on error
  perror("execvp");
  exit(1);

  return 0; // Should not be reached
}