[dforsyth]

On FreeBSD, if we don't call unregister, a stale source is left behind in polling's kqueue implementation.

It becomes impossible to reuse that fd number, resulting in a crash for niri because of an AlreadyExists error (niri-wm/niri#4016).

This change tracks dispatcher registration in register and reregister, and subsequently does unregister (if necessary) when kill is called.

I've only tested this on FreeBSD with niri.

[ids1024]

I'm not really familiar with this part of calloop, but calloop::io appears to be used only by LoopHandle::adapt_io. So I guess in Niri this is failing to unregister the FDs used in on_new_ipc_client? Since that's the only place that uses adapt_io.

It would be good to get one or more unit tests for the behavior here.

[ids1024]

Looks like a reproduction can be as simple as:

use std::os::unix::net::UnixStream;
use std::rc::Rc;

fn main() {
    let event_loop = calloop::EventLoop::<()>::try_new().unwrap();
    let handle = event_loop.handle();

    let socket = Rc::new(UnixStream::pair().unwrap().0);
    handle.adapt_io(socket.clone()).unwrap();
    handle.adapt_io(socket).unwrap();
};

This seems to panic on the second adapt_io call before this PR, but not after.

[codecov]

Codecov Report

❌ Patch coverage is 97.05882% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 85.99%. Comparing base (9252986) to head (6764929).
⚠️ Report is 15 commits behind head on master.

Files with missing lines	Patch %	Lines
src/io.rs	97.05%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #245      +/-   ##
==========================================
+ Coverage   85.47%   85.99%   +0.51%     
==========================================
  Files          14       16       +2     
  Lines        1818     1949     +131     
==========================================
+ Hits         1554     1676     +122     
- Misses        264      273       +9     

Flag	Coverage Δ
macos-latest	85.36% <97.05%> (?)
ubuntu-latest	85.61% <97.05%> (?)

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[ids1024]

Rebased and added 2 unit tests.

Now I understand this and have tests to reproduce this, I'm pretty sure this is correct. Though it looks like src/io.rs could generally use an audit to see if there are issue, or cleaner ways to do things with less unsafe shenanigans.