Backtrace info missing when file descriptors exhausted #686

Consuming all available file descriptors with RUST_BACKTRACE=full
thread 'main' panicked at src/main.rs:19:13:
ran out of file descriptors
stack backtrace:
0:     0x61c61a98b56a - <unknown>
1:     0x61c61a9a7f33 - <unknown>
2:     0x61c61a988fd3 - <unknown>
3:     0x61c61a98b3b2 - <unknown>
4:     0x61c61a98c35c - <unknown>
5:     0x61c61a98c1a2 - <unknown>
6:     0x61c61a98c937 - <unknown>
7:     0x61c61a98c796 - <unknown>
8:     0x61c61a98ba49 - <unknown>
9:     0x61c61a98c45c - <unknown>
10:     0x61c61a959420 - <unknown>
11:     0x61c61a95b2d9 - <unknown>
12:     0x61c61a959ecb - <unknown>
13:     0x61c61a95ab2e - <unknown>
14:     0x61c61a95b961 - <unknown>
15:     0x61c61a98636e - <unknown>
16:     0x61c61a95b93a - <unknown>
17:     0x61c61a95b33e - <unknown>
18:     0x76526c753e08 - <unknown>
19:     0x76526c753ecc - <unknown>
20:     0x61c61a959c95 - <unknown>
21:                0x0 - <unknown>

use libc;
use tempdir::TempDir;
use std::{ffi::CString, io::Write};
use std::{env, fs::File};

fn main() {
    env::set_var("RUST_BACKTRACE", "full");
    println!("Consuming all available file descriptors with RUST_BACKTRACE=full");
    let tmp_dir = TempDir::new("example").unwrap();
    let path : String = tmp_dir.path().join("test").to_owned().into_os_string().into_string().unwrap();
    let mut file = File::create_new(&path).unwrap();
    file.write_all(b"contents").unwrap();

    let mut fds = vec!();
    loop {
        let file_path = CString::new(path.clone()).unwrap();
        let fd = unsafe { libc::open(file_path.as_ptr(), libc::O_RDONLY) };
        if fd == -1 {
            panic!("ran out of file descriptors");
        }
        fds.push(fd);
    }
}