Board:   [fsxNet] Mystic BBS discussion/support
Subject: Only one door per node
From:    Goose (21:1/177)
Date:    Thu Nov 05, 2026 11:23

Hi Gods69,

Yeah, the wiki semaphore trick has exactly that problem: if the door
crashes, the file sticks around and the door is dead until someone
deletes it by hand.

On Linux there's a cleaner way: wrap the door with flock. The kernel
releases the lock as soon as the process dies, crash or not. No stale
lock left behind.

Example for a D3 menu command:

  /usr/bin/flock -n /mystic/locks/mygame.lock /path/to/yourdoor %P

Create /mystic/locks/ once. The lock file itself can stay on disk; what
matters is the active hold. With -n, flock fails immediately if another
node already holds it, so the door never starts twice. You can then show
a short "busy, try later" message (e.g. with a menu ACS / !E check, or
by checking flock's exit code in a tiny wrapper).

Tiny wrapper if you want the busy message:

  #!/bin/sh
  LOCK=/mystic/locks/mygame.lock
  DOOR=/path/to/yourdoor
  if ! flock -n "$LOCK" "$DOOR" "$@"; then
    echo "Sorry, that door is already in use. Try again later."
    sleep 2
  fi

Point D3 at the wrapper instead of the door binary. Same idea works for
DD doors too.

If you want to stay with the wiki semaphore method, a wrapper that
checks whether the door process is still alive and deletes a stale
semaphore first also works. flock is just more robust.

Cheers
Goose

--- Mystic BBS v1.12 A48 (Linux/64)
 * Origin: Goosenet BBS (21:1/177)
.