close_fds

A small Rust library that makes it easy to close all open file descriptors.

OS support

close_fds has three OS support tiers, similar to Rust's support tiers:

Tier 1: "Guaranteed to work" (tested in CI)

• Linux (glibc and musl)
• macOS
• FreeBSD
• Windows (MSVC and GNU toolchains) Note: close_fds does NOT have support for closing open file handles; just file descriptors.

Tier 2: "Guaranteed to build" (built, but not tested, in CI)

• NetBSD

Tier 3: "Should work"

• OpenBSD
• DragonflyBSD

Note: As stated in the license, close_fds comes with no warranty.

OS-specific notes

Here is a list of the methods that iter_open_fds(), iter_possible_fds(), and close_open_fds() will try on various platforms to improve performance when listing the open file descriptors:

• Linux
  • /proc/self/fd if /proc is mounted (very efficient)
• macOS
  • /dev/fd (very efficient)
• FreeBSD
  • /dev/fd if an fdescfs appears to be mounted there (very efficient)
  • The kern.proc.nfds sysctl to get the number of open file descriptors (moderately efficient, unless large numbers of file descriptors are open)
• NetBSD
  • fcntl(0, F_MAXFD) to get the maximum open file descriptor (moderately efficient)

On the BSDs, close_open_fds() may also call closefrom(), which is very efficient.

If none of the methods listed above are available, it will fall back on a simple loop through every possible file descriptor number -- from minfd to sysconf(_SC_OPEN_MAX) (getmaxstdio() on Windows).

Note: The most common use case, close_open_fds(3, &[]), is very efficient on Linux (with /proc mounted), macOS, and all of the BSDs.