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

improve reliability of hang monitor tests

<!-- Please describe your changes on the following line: -->

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

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `___` with appropriate data: -->
- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #___ (GitHub issue number if applicable)

<!-- Either: -->
- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because ___

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

components/background_hang_monitor/background_hang_monitor.rs

@@ -33,17 +33,19 @@ impl HangMonitorRegister {
         monitoring_enabled: bool,
     ) -> Box<dyn BackgroundHangMonitorRegister> {
         let (sender, port) = unbounded();
-        let _ = thread::Builder::new().spawn(move || {
-            let mut monitor = BackgroundHangMonitorWorker::new(
-                constellation_chan,
-                control_port,
-                port,
-                monitoring_enabled,
-            );
-            while monitor.run() {
-                // Monitoring until all senders have been dropped...
-            }
-        });
+        let _ = thread::Builder::new()
+            .spawn(move || {
+                let mut monitor = BackgroundHangMonitorWorker::new(
+                    constellation_chan,
+                    control_port,
+                    port,
+                    monitoring_enabled,
+                );
+                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));
+    if control_sender
+        .send(BackgroundHangMonitorControlMsg::Exit(exit_sender))
+        .is_ok()
+    {
+        // Assert we receive a confirmation back.
+        assert!(exit_receiver.recv().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) {}
+        // Assert we get the exit signal.
+        while !closing.load(Ordering::SeqCst) {
+            thread::sleep(Duration::from_millis(10));
+        }
+    }
 }