# reaperCommand(root:)

- **Package:** libtmux-swift
- **Language:** Swift
- **Kind:** function
- **Source:** https://github.com/libtmux/libtmux-swift/blob/f02a4668570e1cc5198c941413750e021f42c214/Tests/TmuxFixture/TmuxFixture.swift#L295
- **Page:** https://libtmux.org/reference/swift/reapercommand(root-)/

```
reaperCommand(root:)(root: URL) -> TmuxCommand
```

A reaper that outlives this process, so a killed run leaves no server behind.

Arm it in the same invocation that creates the server's first session, and
give it the directory holding the socket. Public because the benchmark
provisions its own servers — with a counting shim standing in for tmux —
and a second copy of this reasoning is a second copy to get wrong.

`defer` and `kill-server` both run *in the process that started the server*,
which makes them useless in the one case that actually leaks: the run is
killed outright by a harness timeout or an impatient operator, and every
tmux server it started survives with no owner and no way to reach it.
Cleanup that depends on the cleaner surviving is not deterministic.

So the reaper lives inside the tmux server instead, as a background job. It
watches the owning process and, once that is gone, removes the directory and
kills the server. Three details carry the design:

- The directory goes first. `kill` ends the server, and tmux kills its jobs
  when it exits, so anything sequenced after it would not run.
- The server is addressed by pid, not by socket, because the socket is
  inside the directory just removed.
- `#{pid}` is left for tmux to expand rather than asked for first, which is
  what lets arming ride in the same invocation that creates the session.
  Sent separately, a run killed in the gap between the two leaves a server
  no reaper ever covered — measurably, under load, about one server in six.
- The interval is whole seconds. Fractions are a GNU and BSD extension that
  POSIX does not require, and a `sleep` that rejects its argument turns this
  into a busy loop per server rather than a slower one. Reaping a second
  later costs nothing here.

## Raises

- `UnsafeReaperRoot`