fix: state lock when emit events (#272)

* fix: state lock when emit events

* test: add deadlock test

crates/loro-internal/src/loro.rs

@@ -438,8 +438,7 @@ impl LoroDoc {
             }
         };
 
-        let mut state = self.state.lock().unwrap();
-        self.emit_events(&mut state);
+        self.emit_events();
         Ok(())
     }
 
@@ -520,8 +519,12 @@ impl LoroDoc {
         ans
     }
 
-    fn emit_events(&self, state: &mut DocState) {
-        let events = state.take_events();
+    fn emit_events(&self) {
+        // we should not hold the lock when emitting events
+        let events = {
+            let mut state = self.state.lock().unwrap();
+            state.take_events()
+        };
         for event in events {
             self.observer.emit(event);
         }
@@ -737,7 +740,8 @@ impl LoroDoc {
             from_checkout: true,
             new_version: Cow::Owned(frontiers.clone()),
         });
-        self.emit_events(&mut state);
+        drop(state);
+        self.emit_events();
         Ok(())
     }
 

crates/loro-internal/tests/test.rs

@@ -792,3 +792,40 @@ fn issue_batch_import_snapshot() {
     let doc3 = LoroDoc::new();
     doc3.import_batch(&[data1, data2]).unwrap();
 }
+
+#[test]
+fn state_may_deadlock_when_import() {
+    // helper function ref: https://github.com/rust-lang/rfcs/issues/2798#issuecomment-552949300
+    use std::time::Duration;
+    use std::{sync::mpsc, thread};
+    fn panic_after<T, F>(d: Duration, f: F) -> T
+    where
+        T: Send + 'static,
+        F: FnOnce() -> T,
+        F: Send + 'static,
+    {
+        let (done_tx, done_rx) = mpsc::channel();
+        let handle = thread::spawn(move || {
+            let val = f();
+            done_tx.send(()).expect("Unable to send completion signal");
+            val
+        });
+
+        match done_rx.recv_timeout(d) {
+            Ok(_) => handle.join().expect("Thread panicked"),
+            Err(_) => panic!("Thread took too long"),
+        }
+    }
+
+    panic_after(Duration::from_millis(100), || {
+        let doc = LoroDoc::new_auto_commit();
+        let map = doc.get_map("map");
+        doc.subscribe_root(Arc::new(move |_e| {
+            map.id();
+        }));
+
+        let doc2 = LoroDoc::new_auto_commit();
+        doc2.get_map("map").insert("foo", 123).unwrap();
+        doc.import(&doc.export_snapshot()).unwrap();
+    })
+}