Auto merge of #27193 - gterzian:fix_monitor_test_timeout, r=jdm

improve reliability of hang monitor tests

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FIX https://github.com/servo/servo/issues/27191

---
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- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #___ (GitHub issue number if applicable)

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because ___

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components/background_hang_monitor/background_hang_monitor.rs

@@ -33,7 +33,8 @@ impl HangMonitorRegister {
         monitoring_enabled: bool,
     ) -> Box<dyn BackgroundHangMonitorRegister> {
         let (sender, port) = unbounded();
-        let _ = thread::Builder::new().spawn(move || {
+        let _ = thread::Builder::new()
+            .spawn(move || {
                 let mut monitor = BackgroundHangMonitorWorker::new(
                     constellation_chan,
                     control_port,
@@ -43,7 +44,8 @@ impl HangMonitorRegister {
                 while monitor.run() {
                     // Monitoring until all senders have been dropped...
                 }
-        });
+            })
+            .expect("Couldn't start BHM worker.");
         Box::new(HangMonitorRegister {
             sender,
             monitoring_enabled,

components/background_hang_monitor/tests/hang_monitor_tests.rs

@@ -197,12 +197,18 @@ fn test_hang_monitoring_exit_signal() {
     );
 
     let (exit_sender, exit_receiver) = ipc::channel().expect("Failed to create IPC channel!");
-    // Send the exit message.
-    let _ = control_sender.send(BackgroundHangMonitorControlMsg::Exit(exit_sender));
 
+    // Send the exit message.
+    if control_sender
+        .send(BackgroundHangMonitorControlMsg::Exit(exit_sender))
+        .is_ok()
+    {
         // Assert we receive a confirmation back.
         assert!(exit_receiver.recv().is_ok());
 
         // Assert we get the exit signal.
-    while !closing.load(Ordering::SeqCst) {}
+        while !closing.load(Ordering::SeqCst) {
+            thread::sleep(Duration::from_millis(10));
+        }
+    }
 }