fix: acquire GIL before AppState write lock to prevent deadlock

src/dispatch.rs

@@ -314,12 +314,17 @@ fn ensure_compiled_snapshot(state: &Arc<RwLock<AppState>>) -> Arc<CompiledRouter
     if let Some(c) = state.read().compiled.as_ref() {
         return Arc::clone(c);
     }
-    let mut st = state.write();
-    if st.compiled.is_none() {
-        st.compiled = Some(Arc::new(st.snapshot_routers()));
-        st.rebuild_snapshot();
-    }
-    Arc::clone(st.compiled.as_ref().expect("just populated"))
+    // Acquire the GIL *before* the write lock: `rebuild_snapshot` needs the GIL to clone
+    // `Py<PyAny>` handles, and taking a Rust lock first would let another thread hold the
+    // GIL while blocked on this same lock — classic AB-BA deadlock (issue #205).
+    Python::with_gil(|_py| {
+        let mut st = state.write();
+        if st.compiled.is_none() {
+            st.compiled = Some(Arc::new(st.snapshot_routers()));
+            st.rebuild_snapshot();
+        }
+        Arc::clone(st.compiled.as_ref().expect("just populated"))
+    })
 }
 
 /// Synchronous RSGI handling for **openapi**, **404**, **405**, and **trivial matched routes**:

src/lib.rs

@@ -748,9 +748,14 @@ impl App {
                 .map_err(|e| {
                     pyo3::exceptions::PyRuntimeError::new_err(format!("DB connect error: {}", e))
                 })?;
-            let mut st = state.write();
-            st.db_pool = Some(pool);
-            st.rebuild_snapshot();
+            // GIL before the write lock (see the comment on `ensure_compiled_snapshot` in
+            // dispatch.rs / issue #205): this future runs on a tokio worker thread without
+            // the GIL, and `rebuild_snapshot` needs it to clone `Py<PyAny>` handles.
+            Python::with_gil(|_py| {
+                let mut st = state.write();
+                st.db_pool = Some(pool);
+                st.rebuild_snapshot();
+            });
             Ok(())
         })
     }
@@ -759,12 +764,12 @@ impl App {
     fn close_database<'py>(&self, py: Python<'py>) -> PyResult<Bound<'py, PyAny>> {
         let state = self.state.clone();
         pyo3_async_runtimes::tokio::future_into_py(py, async move {
-            let pool = {
+            let pool = Python::with_gil(|_py| {
                 let mut st = state.write();
                 let p = st.db_pool.take();
                 st.rebuild_snapshot();
                 p
-            };
+            });
             if let Some(p) = pool {
                 p.close().await;
             }