use backchannel for shutting down monitor

Author: squell

src/exec/use_pty/monitor.rs

@@ -168,7 +168,6 @@ pub(super) fn exec_monitor(
     // Disable nonblocking assetions as we will not poll the backchannel anymore.
     closure.backchannel.set_nonblocking_assertions(false);
 
-    std::thread::sleep(std::time::Duration::from_millis(10));
     match reason {
         StopReason::Break(err) => match err.try_into() {
             Ok(msg) => {
@@ -187,6 +186,14 @@ pub(super) fn exec_monitor(
         }
     }
 
+    // Wait for the parent to give us red light before shutting down. This avoids missing
+    // output when the monitor exits too quickly.
+    let event = retry_while_interrupted(|| backchannel.recv()).map_err(|err| {
+        dev_warn!("cannot receive red light from parent: {err}");
+        err
+    })?;
+    debug_assert_eq!(event, MonitorMessage::ExecCommand);
+
     // FIXME (ogsudo): The tty is restored here if selinux is available.
 
     // We call `_exit` instead of `exit` to avoid flushing the parent's IO streams by accident.

src/exec/use_pty/parent.rs

@@ -349,10 +349,19 @@ impl ParentClosure {
     }
 
     fn run(&mut self, registry: EventRegistry<Self>) -> io::Result<ExitReason> {
-        match registry.event_loop(self) {
+        let result = match registry.event_loop(self) {
             StopReason::Break(err) | StopReason::Exit(ParentExit::Backchannel(err)) => Err(err),
             StopReason::Exit(ParentExit::Command(exit_reason)) => Ok(exit_reason),
-        }
+        };
+        // Send red light to the monitor after processing all events
+        retry_while_interrupted(|| self.backchannel.send(&MonitorMessage::ExecCommand)).map_err(
+            |err| {
+                dev_error!("cannot send red light to monitor: {err}");
+                err
+            },
+        )?;
+
+        result
     }
 
     /// Read an event from the backchannel and return the event if it should break the event loop.