Harden concurrency and resource lifecycle (#101)

crates/libremetaverse/src/appearance_manager.rs

@@ -28,6 +28,7 @@ use libremetaverse_types::{
 use std::collections::{HashMap, HashSet, VecDeque};
 use std::fmt;
 use std::hash::{Hash, Hasher};
+use std::panic::{AssertUnwindSafe, catch_unwind};
 use std::sync::atomic::{AtomicBool, AtomicI32, AtomicU64, Ordering};
 use std::sync::{Arc, Mutex, RwLock};
 
@@ -84,7 +85,8 @@ impl<T: 'static> EventRegistry<T> {
     fn emit_with(&self, mut event: impl FnMut() -> T) {
         let handlers: Vec<_> = mutex(&self.handlers).values().cloned().collect();
         for handler in handlers {
-            handler(event());
+            let argument = event();
+            let _ = catch_unwind(AssertUnwindSafe(|| handler(argument)));
         }
     }
 }
@@ -2291,6 +2293,32 @@ fn inventory_item(value: &dyn InventoryObjectClass) -> Option<InventoryItem> {
 mod tests {
     use super::*;
 
+    #[test]
+    fn event_registry_isolates_panics_and_releases_subscriptions() {
+        let registry = EventRegistry::<usize>::default();
+        let released = Arc::new(());
+        let released_probe = Arc::downgrade(&released);
+        let panicking = registry.subscribe(Arc::new(|_| panic!("subscriber failure")));
+        let delivered = Arc::new(AtomicU64::new(0));
+        let delivered_handler = Arc::clone(&delivered);
+        let releasing = Arc::clone(&released);
+        let healthy = registry.subscribe(Arc::new(move |value| {
+            let _keep_alive = &releasing;
+            delivered_handler.fetch_add(value as u64, Ordering::AcqRel);
+        }));
+        drop(released);
+
+        registry.emit_with(|| 1);
+        assert_eq!(delivered.load(Ordering::Acquire), 1);
+        assert!(released_probe.upgrade().is_some());
+
+        drop(panicking);
+        drop(healthy);
+        assert!(released_probe.upgrade().is_none());
+        registry.emit_with(|| 1);
+        assert_eq!(delivered.load(Ordering::Acquire), 1);
+    }
+
     fn wearable(id: u64, wearable_type: WearableType, asset_type: AssetType) -> InventoryItem {
         let mut wearable = InventoryWearable::new(UUID::new_with_u_int64(id).unwrap()).unwrap();
         wearable.base.set_asset_type(asset_type);