dkl logger: avoid a full thread just to forward signals

src/logger.rs

@@ -1,6 +1,6 @@
 use async_compression::tokio::write::{ZstdDecoder, ZstdEncoder};
 use chrono::{DurationRound, TimeDelta, Utc};
-use eyre::{Result, format_err};
+use eyre::{format_err, Result};
 use log::{debug, error, warn};
 use std::path::{Path, PathBuf};
 use std::process::Stdio;
@@ -9,7 +9,8 @@ use tokio::{
     io::{self, AsyncBufReadExt, AsyncRead, AsyncWrite, AsyncWriteExt, BufReader, BufWriter},
     process,
     sync::mpsc,
-    time::{Duration, sleep},
+    task::spawn_blocking,
+    time::{sleep, Duration},
 };
 
 use crate::{cgroup, fs};
@@ -92,7 +93,7 @@ impl<'t> Logger<'t> {
 
         // forward signals
         if let Some(child_pid) = child.id() {
-            std::thread::spawn(move || forward_signals_to(child_pid as i32));
+            spawn_blocking(move || forward_signals_to(child_pid as i32)).await?;
         }
 
         // handle output
@@ -200,24 +201,29 @@ impl<'t> Logger<'t> {
 
 fn forward_signals_to(pid: i32) {
     use nix::{
-        sys::signal::{Signal, kill},
+        sys::signal::{kill, Signal},
         unistd::Pid,
     };
-    use signal_hook::{consts::*, iterator::Signals};
+    use signal_hook::{consts::*, low_level::register};
 
     log::debug!("forwarding signals to pid {pid}");
 
-    let mut signals = Signals::new([
-        SIGHUP, SIGINT, SIGQUIT, SIGTERM, SIGUSR1, SIGUSR2, SIGPIPE, SIGALRM,
-    ])
-    .expect("signal setup failed");
-
     let pid = Pid::from_raw(pid);
-    for signal in &mut signals {
-        let Ok(signal) = Signal::try_from(signal) else {
+    let signals = [
+        SIGHUP, SIGINT, SIGQUIT, SIGTERM, SIGUSR1, SIGUSR2, SIGPIPE, SIGALRM,
+    ];
+
+    for sig in signals {
+        let Ok(signal) = Signal::try_from(sig) else {
             continue;
         };
-        let _ = kill(pid, signal);
+        unsafe {
+            register(sig, move || {
+                log::debug!("forwarding {signal} to {pid}");
+                let _ = kill(pid, signal);
+            })
+            .ok();
+        }
     }
 }