unregister components while exiting

components/background_hang_monitor/background_hang_monitor.rs

@@ -72,6 +72,8 @@ impl BackgroundHangMonitorClone for HangMonitorRegister {
 pub enum MonitoredComponentMsg {
     /// Register component for monitoring,
     Register(Box<Sampler>, Duration, Duration),
+    /// Unregister component for monitoring.
+    Unregister,
     /// Notify start of new activity for a given component,
     NotifyActivity(HangAnnotation),
     /// Notify start of waiting for a new task to come-in for processing.
@@ -119,6 +121,10 @@ impl BackgroundHangMonitor for BackgroundHangMonitorChan {
         let msg = MonitoredComponentMsg::NotifyWait;
         self.send(msg);
     }
+    fn unregister(&self) {
+        let msg = MonitoredComponentMsg::Unregister;
+        self.send(msg);
+    }
 }
 
 struct MonitoredComponent {
@@ -200,6 +206,12 @@ impl BackgroundHangMonitorWorker {
                     "This component was already registered for monitoring."
                 );
             },
+            (component_id, MonitoredComponentMsg::Unregister) => {
+                let _ = self
+                    .monitored_components
+                    .remove_entry(&component_id)
+                    .expect("Received Unregister for an unknown component");
+            },
             (component_id, MonitoredComponentMsg::NotifyActivity(annotation)) => {
                 let component = self
                     .monitored_components

components/background_hang_monitor/tests/hang_monitor_tests.rs

@@ -105,3 +105,30 @@ fn test_hang_monitoring() {
     // Still no new alerts because the hang monitor has shut-down already.
     assert!(background_hang_monitor_receiver.try_recv().is_err());
 }
+
+#[test]
+fn test_hang_monitoring_unregister() {
+    let (background_hang_monitor_ipc_sender, background_hang_monitor_receiver) =
+        ipc::channel().expect("ipc channel failure");
+
+    let background_hang_monitor_register =
+        HangMonitorRegister::init(background_hang_monitor_ipc_sender.clone());
+    let background_hang_monitor = background_hang_monitor_register.register_component(
+        MonitoredComponentId(TEST_PIPELINE_ID, MonitoredComponentType::Script),
+        Duration::from_millis(10),
+        Duration::from_millis(1000),
+    );
+
+    // Start an activity.
+    let hang_annotation = HangAnnotation::Script(ScriptHangAnnotation::AttachLayout);
+    background_hang_monitor.notify_activity(hang_annotation);
+
+    // Unregister the component.
+    background_hang_monitor.unregister();
+
+    // Sleep until the "transient" timeout has been reached.
+    thread::sleep(Duration::from_millis(10));
+
+    // No new alert yet
+    assert!(background_hang_monitor_receiver.try_recv().is_err());
+}