Fix FD leak after closing child windows

This patch fixes an issue with signal handling where Alacritty would
permanently create one signal handling FD for each alacritty window
created by an instance. This FD was never released, causing a leak of
the FD.

Closes #7983.

CHANGELOG.md

@@ -24,6 +24,7 @@ Notable changes to the `alacritty_terminal` crate are documented in its
 - Dynamic title disabled for new windows when initial one has title as CLI option
 - While terminal in mouse mode, mouse bindings that used the shift modifier and
   had multiple actions only performed the first action
+- Leaking FDs when closing windows on Unix systems
 
 ## 0.13.2
 

alacritty_terminal/src/tty/unix.rs

@@ -19,8 +19,8 @@ use rustix_openpty::openpty;
 use rustix_openpty::rustix::termios::Winsize;
 #[cfg(any(target_os = "linux", target_os = "macos"))]
 use rustix_openpty::rustix::termios::{self, InputModes, OptionalActions};
-use signal_hook::consts as sigconsts;
-use signal_hook::low_level::pipe as signal_pipe;
+use signal_hook::low_level::{pipe as signal_pipe, unregister as unregister_signal};
+use signal_hook::{consts as sigconsts, SigId};
 
 use crate::event::{OnResize, WindowSize};
 use crate::tty::{ChildEvent, EventedPty, EventedReadWrite, Options};
@@ -102,6 +102,7 @@ pub struct Pty {
     child: Child,
     file: File,
     signals: UnixStream,
+    sig_id: SigId,
 }
 
 impl Pty {
@@ -260,13 +261,13 @@ pub fn from_fd(config: &Options, window_id: u64, master: OwnedFd, slave: OwnedFd
     }
 
     // Prepare signal handling before spawning child.
-    let signals = {
+    let (signals, sig_id) = {
         let (sender, recv) = UnixStream::pair()?;
 
         // Register the recv end of the pipe for SIGCHLD.
-        signal_pipe::register(sigconsts::SIGCHLD, sender)?;
+        let sig_id = signal_pipe::register(sigconsts::SIGCHLD, sender)?;
         recv.set_nonblocking(true)?;
-        recv
+        (recv, sig_id)
     };
 
     match builder.spawn() {
@@ -277,7 +278,7 @@ pub fn from_fd(config: &Options, window_id: u64, master: OwnedFd, slave: OwnedFd
                 set_nonblocking(master_fd);
             }
 
-            Ok(Pty { child, file: File::from(master), signals })
+            Ok(Pty { child, file: File::from(master), signals, sig_id })
         },
         Err(err) => Err(Error::new(
             err.kind(),
@@ -296,6 +297,10 @@ impl Drop for Pty {
         unsafe {
             libc::kill(self.child.id() as i32, libc::SIGHUP);
         }
+
+        // Clear signal-hook handler.
+        unregister_signal(self.sig_id);
+
         let _ = self.child.wait();
     }
 }